What exact characters determine an animal's Genus?

What exact characters determine an animal's Genus?

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I do know that if two animals cannot naturally reproduce, they are said to be of two different species. But what determines the genus?

Just for example, the African elephant belongs Loxodonta but the Indian counterpart belongs to Elephas , despite the fact that they are so similar, as opposed to say, the fact that, the Bengal Tiger and the Snow leopard despite being so different , are placed in one genus, Panthera ?

I don't think there is any non-arbitrary concept being used to tell whether two species belong to the same genus or not. The same goes on with any other taxonomic rank. Systematicists build some intuition within each clade about what a genus could mean and use it to argue what is the most strategic grouping but the concept of genus may well vary a lot from clade to clade (from spiders, to mammals or to flowering plants,… ).

Note that even the concept of species is not as nicely defined as you may think. Have a look at How could humans have interbred with Neanderthals if we're a different species? for discussion on the concept of species.

What also SciShow forgot to mention is that, by the very definition of evolution, taxonomy is just a handy way that we invented to simplify our life (or complicate, if you ask me). As they pointed out, categorizing and identifying appeals to our brain. But it's just a photo of a runner; if you snap it a few seconds (or geological eras) apart then you get the runner in a different position.

Reminds me of a riddle I was told some time ago: "where was the men when he jumped off the bridge?". If your answer is "in the air", well that's AFTER he jumped… likewise "on the bridge" is BEFORE he jumped.

So what we today identify as a specific species or genus might very well change in the future decades or even years and taxonomy is full of cases in which species where "relocated" and renamed. Sometimes changing the parameter on which you build the taxonomy (mostly now is gene based, before it was morphology based) might completely turn the tree upside down from the roots. Plant taxonomy (being a botanist that's what I'm familiar with but I suppose it happened also with animals) was revised multiple times because some clades would change position depending which gene was used as reference.

What exact characters determine an animal's Genus? - Biology

A pig is any of the animals in the genus Sus, within the even-toed ungulate family Suidae. Pigs include domestic pigs and their ancestor, the common Eurasian wild boar (Sus scrofa), along with other species. Pigs, like all suids, are native to the Eurasian and African continents, ranging from Europe to the Pacific islands. Suids other than the pig are the babirusa of Indonesia, the pygmy hog of South Asia, the warthog of Africa, and other pig genera from Africa. The suids are a sister clade to peccaries.

Juvenile pigs are known as piglets. [1] Pigs are highly social and intelligent animals. [2]

With around 1 billion individuals alive at any time, the domestic pig is among the most populous large mammals in the world. [3] [4] Pigs are omnivores and can consume a wide range of food. [5] Pigs are biologically similar to humans and are thus frequently used for human medical research. [6]

Structure and Function

Viruses are inert outside the host cell. Small viruses, e.g., polio and tobacco mosaic virus, can even be crystallized. Viruses are unable to generate energy. As obligate intracellular parasites, during replication, they fully depend on the complicated biochemical machinery of eukaryotic or prokaryotic cells. The main purpose of a virus is to deliver its genome into the host cell to allow its expression (transcription and translation) by the host cell.

A fully assembled infectious virus is called a virion. The simplest virions consist of two basic components: nucleic acid (single- or double-stranded RNA or DNA) and a protein coat, the capsid, which functions as a shell to protect the viral genome from nucleases and which during infection attaches the virion to specific receptors exposed on the prospective host cell. Capsid proteins are coded for by the virus genome. Because of its limited size (Table 41-1) the genome codes for only a few structural proteins (besides non-structural regulatory proteins involved in virus replication). Capsids are formed as single or double protein shells and consist of only one or a few structural protein species. Therefore, multiple protein copies must self assemble to form the continuous three-dimensional capsid structure. Self assembly of virus capsids follows two basic patterns: helical symmetry, in which the protein subunits and the nucleic acid are arranged in a helix, and icosahedral symmetry, in which the protein subunits assemble into a symmetric shell that covers the nucleic acid-containing core.

Table 41-1

Chemical and Morphologic Properties of Animal Virus Families Relevant to Human Disease.

Some virus families have an additional covering, called the envelope, which is usually derived in part from modified host cell membranes. Viral envelopes consist of a lipid bilayer that closely surrounds a shell of virus-encoded membrane-associated proteins. The exterior of the bilayer is studded with virus-coded, glycosylated (trans-) membrane proteins. Therefore, enveloped viruses often exhibit a fringe of glycoprotein spikes or knobs, also called peplomers. In viruses that acquire their envelope by budding through the plasma or another intracellular cell membrane, the lipid composition of the viral envelope closely reflects that of the particular host membrane. The outer capsid and the envelope proteins of viruses are glycosylated and important in determining the host range and antigenic composition of the virion. In addition to virus-specified envelope proteins, budding viruses carry also certain host cell proteins as integral constituents of the viral envelope. Virus envelopes can be considered an additional protective coat. Larger viruses often have a complex architecture consisting of both helical and isometric symmetries confined to different structural components. Small viruses, e.g., hepatitis B virus or the members of the picornavirus or parvovirus family, are orders of magnitude more resistant than are the larger complex viruses, e.g. members of the herpes or retrovirus families.

What exact characters determine an animal's Genus? - Biology

Notes for Chapter 10:
Classification and Phylogeny of Animals

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Ch. 10: 196-207 RQ10: 2-7, 9
see here for help on RQ10:7

Introduction: Order in diversity
Featured Animal : Cone shell,
Conus sp.
(these are cool snails with deadly toxins - see one nail and devour a passing fish with its harpoon-like radular tooth by downloading the movie at link 8)
Links: 1 - 2 - 3 - 4 - 5 - 6 - 7 - 8 - 9

I. Linnaeus and the Development of Classification

Key Terms : hierarchical system, taxa (taxon), taxonomic ranks, binomial nomenclature, genus, species

A. Discovering pattern and classifying

1. Systematists have three goals:

a. discover all species
b. reconstruct phylogeny (genealogical relationships)
c. classify according to phylogeny

2. Taxonomy: system for naming and classifying
3. Systematics: includes taxonomy but also phylogenetic and evolutionary studies

B. Linnaeus and the Linnaen System

1. Classifying dates at least back to Aristotle in ancient Greece
2. John Ray (English) refined classification and notions of species
3. Current binomial classification system introduced by Linnaeus

a. Linnaeus was Swedish botanist whose specialty was flowering plants
b. His more ambitious Systema Naturae classified animals and plants

4. Linnaeus introduced concept of taxomic hierarchy (Table 10-1)

a. He had 7 major ranks: kingdom, phylum, class, order, family, genus, species.
b. Taxa (singular: taxon) are names at any rank (e.g., Animalia)
c. Today taxa are usually subdivided (e.g., superclass, suborder, etc.)
d. Some groups are divided into many levels (30 for insects)

5. Linnaeus introduced binomial nomenclature

a. Each animal name has two words (binomial) as in Turdus migratorius.
b. Genus is capitalized species is lower case
c. By convention, always italics (Turdus migratorius) or underlined
d. Never use species name alone always include genus
e. For animals, genus names must be unique
f. Higher-level taxa not italicized but capitalized (e.g. Reptilia).
g. Trinomial names sometimes used to indicate geographic subspecies

II. Taxonomic Characters and Phylogenetic Reconstruction

Key Terms : phylogeny, characters, homology, homoplasy

A. Using Character Variation to Reconstruct Phylogeny

Key Terms : ancestral vs. derived character states, polarity (the ancestral state is generally the one that is also present in the outgroup, by outgroup comparison), clade (ancestor plus all its descendents), synapomorphy (derived novelty that helps us recognize a clade, e.g., feathers in birds), plesiomorphy (ancestral or "primitive" state, not necessarily the most "simple" state), nested hierarchy, symplesiomorphic (shared "primitive" similarities - these do NOT help us recognize clades, e.g., lack of backbone in a fly and a snail), cladogram vs. phylogenetic tree (similar, but the "y-axis" of a cladogram means nothing, whereas it might in a phylogenetic tree, e.g., geological time) - Note: Don't worry, these terms are difficult at first and we will be reinforcing them over the entire semester -- See Cladogram Exercise 1.

1. Estimating a phylogeny depends on characters (traits)

a. only characters that vary are interesting
b. the different forms of the charater are termed states

2. One observes similarities that could be homologous

a. a homology is a similarity due to common ancestry
b. this means the common ancestor had the same state
c. a homologous similarity only has to evolve once

3. Alternatively, similarities might have evolved separately (convergently)
4. Any similarity not due to homology is termed a homoplasy (includes convergence)
5. The parsimony criterion is used to choose some trees as better than others

a. The most parsimonious tree explains as much as possible by homology
b. A tree is more parsimonious than another when it requires fewer changes
c. The most parsimonious tree is the one with the least homoplasy
d. This is because homoplasies require extra changes homologies do not

B. Study of Character Variation Can Reveal Ancestral Conditions

1. Given a phylogeny, one can determine which character state is ancestral
2. The ancestral state of a character is the state found in the ancestor
3. Character states arising later are termed derived states
4. In practice, we cannot normally observe the common ancestor

a. Instead we use a closely related taxon as an outgroup to estimate ancestral state
b. We can also use multiple outgroups
c. Example: we observe no teeth in birds and teeth in lizards which is primitive?

1) We note that outgroups (e.g., mammals, salamanders and fish) all have teeth
2) Thus, the common ancestor of birds and lizards probably had teeth
3) Thus, the presence of teeth in lizards is a primitive state
4) Thus, the lack of teeth in birds is a derived state

5. A clade is a natural taxon of organisms bound in space and time

a. A clade is defined as a common ancestor and all of its descendants
b. In practice, we recognize a clade by its derived similarities
c. Example: clade - birds includes ancestor of birds and all its descendants
d. Feathers is a derived similarity found only in birds (no living outgroup has feathers)
e. It is most parsimonious to suppose that the common ancestor of birds was feathered
f. Because lizards lack feathers, feathers probably arose after lizards and birds diverged
g. In other words, the last common ancestor of lizards and birds lacked feathers

6. Technically, a derived character state is termed an apomorphy
7. A shared derived character state is termed a synapomorphy
8. Synapomorphies are typically nested hierarchically

a. Example: All placental mammals have a placenta placenta is a synapomorphy
b. All marsupial mammals have a marsupial pouch and lack a placenta
c. Both placentals and marsupials have hair and mammory glands (as do all mammals)
d. mammals and lizards both have an amnion around their eggs (as do all amniotes)
e. amniotes and salamanders both have four limbs (as do all tetrapods)
f. tetrapods and sharks both have jaws (as do all gnathostomes)

9. An ancestral (not derived) state is termed a plesiomorphy
10. A shared ancestral state is termed symplesiomorphy.

C. Sources of Phylogenetic Information

Key Terms : comparative morphology, biochemistry, and cytology

1. Morphology: includes shape, size, and development

a. Examples: Skull or limb bones, scales, hairs, feathers
b. Can be observed in fossils as well as living specimens

2. Biochemical comparison (now the most common evidence used)

a. Examples: Protein or DNA sequence comparison
b. Occasionally fossils have remnants of DNA preserved, but not easy to recover

a. Examples: examines variation in number, shape and size of chromosomes
b. Only used for living organisms

4. Dating a fossil is possible (with radioactive dating methods)
5. Estimating when lineages diverged is also possible with sequence comparisons

Key Terms : monophyly, paraphyly, polyphyly

1. Three types of groupings are recognized

a. Monophyletic: includes common ancestor and all its descendants
b. Paraphyletic: includes common ancestor and only some of its descendants
c. Polyphyletic: does not include the most recent common ancestor of its members

2. Evolutionary and cladistic systematists only disagree about the case of paraphyletic groups

a. Both agree monophyletic groupings should be recognized
b. Both agree polyphyletic groupings should be rejected
c. Only evolutionary systematists allow paraphyletic groups
d. In contrast, cladists only formally name groups thought to be monophyletic
e. The cladistic principle is known as the "rule of monophyly"
f. Many taxa in widespread use are paraphyletic

Note: The following section of the text, which contrasts evolutionary and cladistic approaches, is understandably sympathetic to the former. First, evolutionary taxonomy is pervasive throughout the text, and would require a major rewriting effort by the authors to eliminate. Second, the authors understandably do not want to alienate those instructors who are not yet ready to conform strictly to the rule of monophyly as would be required by an entirely cladistic approach. They want to sell as many textbooks as they can. However, such an approach is possible and would be wonderful to see, in my opinion. This is because cladistic classifications have essentially taken over the field of animal classification. Any doubters need only browse GenBank's Taxonomy Browser to see a working system of classification that includes all organisms and strictly conforms to the rule of monophyly. It works and is much simpler than the older evolutionary taxonomies it replaces. Moreover, emphasis of paraphyletic groups has a well documented tendency to confound phylogenetic understanding, often in subtle and insidious manner. The following notes under the "Key Terms" sections should suffice to characterize the distinctions between these schools, which need to be studied primarily to appreciate how to recognize the distinction between the older evolutionary taxonomy approach (still wildly popular thanks to the common use of paraphyletic group names in common usage and by the unwillingness of textbook authors to rock the boat) and the current cladistic approach as employed by most practicing systematists.

Also see here for help with the related RQ 10:7.

A. Traditional Evolutionary Taxonomy

Key Terms : evolutionary taxonomy (i.e., older approaches that are common in this text but are not emphasized in this class, you will be expected to recognize when a grade is not necessarily a clade), adaptive zone (old-fashioned approach where a group of animals is "elevated" to a higher rank in a classification because it has diversified into a new ecological realm, e.g., birds, humans), phenetic taxonomy (grouping by overall similarity, both synapomorphies and symplesiomorphies - this approach has been mostly abandoned - current systematists agree that only synapomorphies can provide evidence of monophyly of a group)

B. Phylogenetic Systematics/Cladistics

Key Terms: sister group , cladistics (this is the approach most commonly emphasized today and the one that will be used in this class, but note that there is relatively little controversy about how to find the best phylogenetic tree for a group, but much more controversy about how to turn this tree into a classification, e.g., whether or not to allow known paraphyletic taxa to have formal taxon names -- in this class we say NO, only monophyletic groups should have formal names -- this is the "Rule of Monophyly")

C. Current State of Animal Taxonomy

IV. Species (Please read - this should be review from Biol. 131)

V. Major Divisions of Life (skip - tree has major flaws)

VI. Major Subdivisions of the Animal Kingdom (skip - very old-fashioned)

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Carnivorous Poromya

Anatomy of Protobranchia


In all Poromya species examined, an inhalant siphon is used to get food. Hydraulic pressure changes within the mantle cavity controls extention and enlargment of the of the siphon. Blood is moved from a reservoir into the mantle cavity to produce this pressure change. The siphon is returned to the body by pallial retractor muscles excess water is transferred to a smaller exhalant siphon. Originally it was thought that the tentacles of Poromya, generally 15 in number, were responsible for prey capture. These have since been observed not to be sticky, as was previously thought, but instead are cilia, mechanosensory organs which allow Poromya to sense the movement of prey.(Morton 1987) There is little data on the exact neural networks that coordinate this behavior, so external motion necessary to cue siphon-based feeding is not well understood.


The development of carnivorous feeding is not well understood. Few studies characterize the chemosensory cilia that alert Poromya of nearby food, let alone how these cilia affect feeding practices over time. It is not clear at what point Poromya become carnivorous, or whether their diet changes as a result of previous learning.


Given similar prey capture mechanisms, including the use of an enlarged siphon and ciliary-sense organs, this behavior is likely monophyletic, and produced as early as the Palaeozoic period (540-250 million years ago). As noted, mass extinction then, as well as in the Mesozoic period (250-66 million years ago) make further characterization difficult.

One particular study, conducted by Brian Morton in 1987, undertook a broad phylogenetic discussion of Parilimyidae, Verticordiidae, Poromyidae, and Cuspidariidae, all of which exhibit carnivorous behavior and all of which are found within the taxonomic order Anomalodesmatans. Poromyidae and Cuspidariidae are extant, while Parilimyidae and Verticordiidae are not. The study concludes:

"On the basis of this study, a better picture of phylogenetic affinities in these related bivalves is possible. The stem group seems to be represented by verticordiids and parilimyids. Most verticordiids are of relatively simple plan and their siphonal prey-capture mechanism comparatively unspecialized. Parilimyids and Lyonsiella, however, have a pair of taenioid muscles, enhancing the efficiency of siphonal retraction. Lyonsiella formosa (at least) feeds like poromyids, suggesting a phylogenetic link the latter, however, being the more morphologically specialized. Cuspidariids, like parilimyids, feed on swimming prey, the long inhalant siphon being everted upwards. This also suggests a phylogenetic link, the cuspidariids being the more specialized members of this group. The Palaeozoic and Mesozoic extinctions of large numbers of anomalodesmatans have left few living descendants and these show widely divergent character traits, making the construction of lineages difficult."(Morton 1987)

Adaptive Value

As discussed in the previous section on phylogeny, carnivory in bivalves has a long history tracing back to the Mesozoic period, possibly further, and is well adapted for extant species.One study examining the stomach contents of Poromya found a partially digested ostracod (the species was not identified). Another specimen contained a relatively intact cirolanid isopod (also unidentified).(Leal 2008)

Scavenging, filter-feeding, and carnivory have existed within Bivalvia since the Mesozoic period, 250 million years ago, demonstrating these behavioral strategies to be of excellent adaptive value. Many questions relating to the origin of these different feeding behavioral practices remain. Of particular note to this discussion is whether one feeding strategy is or was in the past of greater adaptive benefit than other existing strategies. Carnivory is certainly a more efficient feeding strategy than the endosymbiosis found in Entovalva or the chemoautotrophy of Solemyidae and Lucinidae, indicated by Poromya's increased size and larger geographical spread. However, whether it is of greater adaptive value than scavenging or the filter-feeding more common among bivalves is more difficult to determine. Does a greater number of species practicing these strategies suggest greater adaptive value? Does the potential for evolutionary modification between species practicing these strategies speak to the degree of the behaviors' adaptabilities?

Sexual Reproduction

Most animals engage in sexual reproduction: two individuals have some form of sex, combine their genetic information, and produce offspring bearing the DNA of both parents. (Exception alert: some animals, including certain species of sharks, are capable of reproducing asexually.) The advantages of sexual reproduction are huge, from an evolutionary perspective: the ability to test out various genome combinations allows animals to adapt quickly to new ecosystems, and thus out-compete asexual organisms. Once again, sexual reproduction isn't restricted to animals: this system is also employed by various plants, fungi, and even some very forward-looking bacteria!


That genus and seven other related living ones make up the Camponotini ant “tribe,” all of which have bacteria inside their gut cells.

He and colleagues assigned the fossil, which was eroding out of previously dated sediment at a site called Ramnagar, to a new genus and species, Kapi ramnagarensis.

The reptile, from the genus Guizhouichthyosaurus, lived during the Triassic Period about 240 million years ago.

Many modern animals have close relatives — other species that are in their same genus .

So while they couldn’t say what animal genus the prints belonged to, they were able to determine that they were in the footprint genus Batrachopus.

The genus -species distinction that we still use is a legacy of Aristotle.

Many products list only the genus and species, but different strains provide different benefits (more on that later).

The most common probiotic bacteria come from two genus groups: Lactobacillus or Bifidobacterium, although there are many others.

Others in the vast genus of viruses—at least 100—cause human disease.

He has studied the Vibrio genus of bacteria for more than 40 years and still finds it eminently fascinating.

Thus we see that these two lines bear towards each other the relation of genus and species.

The sexual cycle can take place only within the body of one genus of mosquito, anopheles.

M. Peron says that it forms a new genus , and of a very remarkable character.

This genus appears to be nearly allied to the Agamae, but differs from them in the peculiar frill that is appended to the neck.

There are two other species of this genus in Captain King's collection, which appear to be new.

The Subspecies Concept

In the early days of mammalian research, places where mammals were collected tended to be scattered about, with lots of gaps between collection stations. It often was found that two stations had kinds of mammals that were similar, but yet recognizably different. A sample of one kind of mice, for example, might be overall similar to one from another station, but with some differences in color, in length of tail, size of ears, etc. Since these were recognizably different they often were named as separate species, usually within the same genus. As geographic gaps were filled in, however, not uncommonly the mammals from the intermediate sites were intermediate in character states. Eventually, then, these animals were recognized as actually being members of the same species despite some differences. Various terms were used to designate them taxonomically, with eventually the term "subspecies" winning out.

The subspecies is the only formal rank recognized below the level of species (we do not recognize varieties or races as separate entities from subspecies under the International Code of Zoological Nomenclature). It shares with supraspecific categories the lack of objectivity, but this seems to be a somewhat greater mental problem for biologists than for, e. g., the genus category. Possible reasons are that there are more potential subspecies than genera and that the subspecies concept is (or should be) a population concept, whereas the supraspecific categories are not, at least in the Mendelian sense.

(Biological) species and subspecies are populational concepts in the sense that gene flow is at least potentially possible among members of the taxon. With the subspecies concept, there is a defined geographic component to the definition. A widely accepted definition is that of Mayr and Ashlock (1991:43): "A subspecies is an aggregate of phenotypically similar populations of a species inhabiting a geographic subdivision of the range of that species and differing taxonomically from other populations of that species." Mayr and Ashlock also recognize that there may be temporal separation rather than geographic separation, and so fossil subspecies differing from modern populations may be recognized.

Several features need to be emphasized. For one, it is the populations that are phenotypically similar, not necessarily individuals. Thus individuals within a subspecies may differ from other individuals in morphological character states, but do not form separate subspecies, instead merely indicating that the population is polymorphic. Another important point is the geographic component. Since members of different subspecies are members of the same species, then by definition of the biological species, they can interbreed given the opportunity sympatric populations interbreeding would quickly break down any differences between them and the subspecies would disappear as separate entities. Indeed, the major practical question asked to determine whether two taxonomically different populations are members of the same species (and thus represent subspecies of that species) or not (that is, are different biological species) is, "Do they occur sympatrically anywhere during the breeding season with no evidence of free interchange of genetic material?" If they do, then they likely are separate species. The geographic component is so prominent, that subspecies sometimes are called geographic races.

Let me head off what seems to be a common misconception among beginning biologists. Namely, that a subspecies somehow is an entity entirely separate from a species. Subspecies have no existence separate from the species of which they are a part. Thus either a species has no subspecies (are monotypic: there are no subdivisions of it that differ taxonomically from other subdivisions) or it is made up of two or more subspecies (are polytypic), and there is nothing left over that is not part of one of the constituent subspecies.

Other important points to consider is that virtually every population differs to some degree from every other population of a species due to stochastic processes and, perhaps, microevolutionary events within the population. Thus variation among populations making up a single subspecies is expectable. In earlier days,it was considered (by some) to be legitimate to name as a subspecies any population that could be shown to be statistically different from other populations of the species. Eventually it became evident to most that, given a large enough sample size, any two reasonably sized populations could be shown to differ. Since any utility at all would be lost by naming each local population, the idea of "taxonomic" difference comes into play&mdashbut, as noted, how much difference is required for it to be a taxonomic difference is subjective, and there has been limited success in getting systematists to agree on the magnitude of that difference.

The populational aspect also causes some problems with individuals who have difficulty thinking populationally. For example, by the conception of most systematists, there is no requirement that every individual of a subspecies be phenotypically identifiable as belonging to that subspecies as opposed to a different subspecies. The reason, of course, is that it is the populations that must differ taxonomically. To make the point, we might go to the absurd and postulate one population of a species consisting of 80% albinos and a different population consisting of 5% albinos. The two populations definitely are different (and I won't argue whether this is a taxonomic difference or not), but having in hand an albino individual does not allow that individual to be identified to subspecies unless the geographic location from which it was taken is known.

Another problem is that there may be independent occurrences of phenotypically similar populations in different geographic areas (when considered the same subspecies, these are called polytopic subspecies). This may be because of parallel evolution due to environmental selective features&mdashthe common example of dark populations of various animals on basaltic lava beds is typical. I have argued elsewhere that they should not be considered members of the same subspecies because the defining taxonomic characters have not been inherited from a common ancestor.

Yet another problem is based on selection of characters. Often phenotypic characters vary independently geographically. For example, size might vary from north to south, while tail length might vary from east to west. Some workers have suggested that subspecies should be named only when characters are correlated geographically.

Many characters vary clinally (a cline is a character gradient through space [or time]). Some systematists would recognize subspecies in a geographically continuous, clinal distribution only if there is a narrow geographic region of rapid change in character states (a step cline). Otherwise, any boundary drawn between subspecies along the cline would be entirely arbitrary.

Since, by definition, individuals of different subspecies will interbreed when they have the opportunity, we normally expect to find a zone of intergradation between subspecies that do come into contact with one another geographically. Any attempt to name individuals within the zone as belonging to a particular subspecies is of little value (sometimes to emphasize the intermediate characteristics, the "x" symbol may be used e.g., Peromyscus maniculatus blandus x rufinus. However, the "x" symbol more commonly is used to indicate a hybrid between two species).

In practice, the subspecies may be a useful tool, but must be used with caution and pretty much requires familiarity with the particular species and what philosophy has been used to name the subspecies within that species.

Centennial Museum and Department of Biological Sciences, The University of Texas at El Paso

The Genus Hydnora

Recent research on the genus Hydnora is reviewed. Hydnora is tentatively considered to consist of four species: H. johannis, H. triceps, H. esculenta, and H. africana. Notes on the floral biology, distribution, nomenclature, economic importance, and uses are given with emphasis on H. triceps(1).

The Hydnoraceae, with only two genera Hydnora and Prosopanche, includes some of the strangest plants in the world. Hydnora is found in the semi-arid regions of Africa and southern Arabia while Prosopanche grows in similar habitats in South and Central America. The vegetative plant body is highly reduced consisting of only roots and flowers. In fact, the Hydnoraceae are the only known angiosperms with no leaves or scales of any sort. Both genera are holoparasites and are totally dependent upon their hosts for their existence. Only the flower emerges from the soil. The extreme reduction limits the number of taxonomic characters and has raised questions as to their phylogeny. The Hydnoraceae has been allied with several different groups, eg, the recent summary in Nickrent and Franchina (1990). Previous work on Hydnora is summarized in Musselman and Visser (1989) but due to their furtive nature and seasonal appearance, they remain poorly known plants. This paper is a review of some of my current work on the systematics and biology of the genus based on herbarium and fieldwork, with a key to species and notes on each species.

Hydnora Thunberg, Kongl. Vetensk. Acad. Handl. 36: 69. 1775. Hydnora Aphyteia Linnaeus, Pl. Aphyteia, p. 7. 1776. TYPE: H. africana Thunberg, 15452, UPS!(2)

Subterranean holoparasitic herbs with often massive root systems spreading laterally from the host. Roots up to 1 dm wide 4-5 angled, terete or sometimes flattened. Flowers 3, 4, or 5merous. Perianth lobes patent and resting on the soil, or lobes not reflexed and flower opening by a separation of the lobes. Flowers variable in size from 5-25 cm, the length depending on the depth of the root, pedicel 4-9 cm. Ovary inferior, with numerous infolded, pendant placentae unilocular. Stigmas sessile, intricately grooved. Androecium complex, with stamens fused. Pollen monocolpate. Perianth lobes 6-8 cm in some species "bait bodies" are present between the inner marginsof the lobes in other species a well developed osmorphoric region ("cucullus") is present. Fruit fleshy.

Key to Species of Hydnora

AA. Flowers 5-merous, imperfect. 1. H. esculenta.

AA. Flowers 3 or 4-merous (rarely 5), perfect. BB.

BB.Flowers 3-merous (rarely 4), cucullus absent roots strongly angled. CC.

BB. Flowers 4-merous (rarely 3 or 5), cucullus present roots not strongly angled. 2. H. johannis.

CC. Flower 5-8 cm long perianth lobes forming a hood. 3. H. triceps.

CC. Flowers 1-15 cm long hood absent. 4. H. africana.

1. Hydnora esculenta Jumelle & Perrier de la Bathie. Restricted_to Madagascar, this species has not been collected since 1947. I have found only four collections of this unusual species. A deliberate search should be made to determine if it is still extant. Hydnora esculenta is perhaps the most specialized of all members of the genus as the flowers are unisexual. The pistillate plants apparently have well developed staminodes.

2. Hydnora johannis Beccari. I consider the following as synonyms: H. abyssinica A. Braun, H. abyssinica var. quinquefida Engler, H. angolensis Decaisne, H. bogoensis Beccari, H. cornii Vaccaneo, H. gigantea Chiovenda, H. hanningtonii Rendle, H. michaelis Peter, H. ruspolii Chiovenda, and H. solmsiana Dinter. In 1873, Decaisne also described H. aethiopica apparently based on a specimen from Sabatier's expedition (Decaisne, 1873 in Musselman and Visser, 1989). However, this name appears to be based on an incomplete specimen. This is the most widespread and frequently collected Hydnora. It is known from western Namibia, northern Botswana, Zimbabwe, Zaire, Tanzania, Kenya, Ethiopia, Somalia, along the Blue Nile to Khartoum in Sudan and in the Arabian Peninsula in southern Saudia Arabia, northern Yemen, and only recently from the Dhofar region of Oman. Except for one report of Albizzia, (Shantz, 198, K, as H. hanningtonii) the hosts for H. johannis are always species of Acacia. This is the only Hydnora known to be of any economic importance. In Ethiopia it has been reported to break up the pavement of roads (Parker, 1988) and likewise to break up cement floors in Sudan (Musselman, unpublished).

3. Hydnora triceps Drege & Meyer. In 1988 Visser discovered a_large population of this very poorly known plant which was thought extinct because it had been collected only a few timessince its discovery in the 1830's. Like H. africana, it parasitizes shrubby species of Euphorbia. Visser was able to visit this population only once before his death and found that Hydnora triceps represents yet another pollination syndrome within the genus. His preliminary work (Visser, 1989 and personal communications) indicates that bait bodies are present and that they attract blowflies which lay their eggs within the flower where the larvae develop. The flowers of H. triceps apparently develop only underground and do not emerge from the soil. Insects enter the flowers through soil cracks.

This remarkable adaptation to underground pollination deserves verification and further investigation. In fact, many angiosperms have underground flowers but inevery instance the flowers are actually produced above ground and grow underground to develop fruits (as in the common peanut), or are cleistogamous and borne right at the soil surface (as in many violets), or flower under litter or duff. These are not truly subterranean, however, in that the flower does not open beneath the soil. Subterranean flowering is extremely rare in the angiosperms and the only other documented case is that of the orchid genus Rhizanthella, endemic to Australia with two species (Jones,1988). No subterranean flowering dicots are known. In a popular account of the biology of Rhizanthella Sherwin Carlquist makes several statements pertinent to the study of H. triceps (Carlquist, 1965). "How does a flower manage a completely underground existence?" And, "Rhizanthella's habits are not only mysterious, we have no idea how or why such an orchid has evolved at all".My examination of material of H. triceps suggest that its flower structure and vernation are well adapted to a subterranean existence. Unlike any other Hydnora, the perianth lobes are connate in such a way that the only opening into the flower isthrough slits on the side of the floral tube. This hood-like structure ensures that the orifice is not occluded by soil as the flower grows towards the surface. This may be one way that it manages ". a completely underground existence". Further field studies are necessary to discover other adaptations.

What are the plant-insect relationships in H. triceps? First, the insects which can be pollen vectors in H. triceps need to be determined. The pollinator fidelity of the insects also needs study. Put another way, does H. triceps have a highly specialized pollinator which is dependent upon this plant either for its food source as a place for reproduction? In other species of Hydnora, pollinators harvest pollen (eg, Musselman and Visser, 1989). The situation in H. triceps is not clear and can only be determined by field observations. What is the possible relationship between the pollination of H. triceps and its host, Euphorbia dregeana E. Mey. ex Boiss. and other nearby plants? The fruit of H. triceps has never been described.

The name Hydnora triceps was first used by Meyer in 1838 based on a specimen collected by Drege in Namaqualand in southern Africa. The proper citation of this name would be Hydnora triceps Drege et Meyer. However, an Englishman by the name of W. J.Burchell traveled in southern Africa earlier in the 1800s and published an account of his travels in 1822 (Burchell, 1822). In1826, K. Sprengel in his Systema Vegetabilium cites the name Aphyteia multiceps. According to the rules of botanical nomenclature, this is a validly published name because Sprengel based it on the description of Burchell in which case the name would be cited as Aphyteia multiceps Burchell & Sprengel. Plants examined by Sprengel were usually kept in the large herbarium at Berlin and since the herbarium at Berlin was largely destroyed during World War II. The correct application of the name could only be clarified by noting the original description of the plant in question by Burchell. In this book in a footnote to page 213 Burchell (1822) notes:"Aphyteia multiceps, B., is a new species, found in the more western parts of this Karro, and of which I received a specimen from my friend Hesse, to whom it had been sent from the district of Clan William or the Elephant's River. It is easily distinguished, by a subterraneous stem, about two inches long, clothed with a few large scales, as in all radical parasitic plants, and producing, in a close head, several flowers, (in my specimen, five,) which had not the appearance of being succeeded by a seed-vessel of the magnitude at all proportionable to that of A. Hydnora.

This description clearly indicates that it can NOT be a species of Hydnora as no scales or multiple flowers are present in Hydnora. It is not certain which plant Burchell was referring to but my guess would be that it is one of the Balanophoraceae, perhaps Sarcophyte sanguinea which occurs in South Africa (Visser, 1981).

4. Hydnora africana Thunb. Synonyms: H. longicollis Welw., H. tinctoria Welw. (each of these names apparently a nomen nuda), H. africana var. longicollis Welw. Known to parasitize only shrubby species of Euphorbia. This is the best known of all Hydnora species even though it is restricted in distribution to a small stretch of southern Africa from the Cape Province as fare east as Swaziland.

In a review of floral biology of H. africana (Visser, 1981) and H. johannis (Musselman, 1984 Musselman and Visser, 1989) it was found that beetles pollinate the flowers but in remarkably ifferent ways. Hydnora johannis is visited mainly by scarib eetles (Musselman, 1984) which are attracted by a distinct osmophore ("cucullus") on the adaxial surface the perianth lobe. Hydnora africana, on the other hand, lacks such cuculli but has "baitbodies", specialized perianth hairs which omit the odor of decaying leather and attract various dermestid beetles (Visser and Musselman, 1986 and Visser, personal communications).

Hydnora africana is the only member of Hydnoraceae which has been cultivated. The following account is adapted from Carlquist (1989).

In December, a visit to the Karoo Garden in Worcester revealed that on a nearby hillside, some of the older Euphorbia mauritanica shrubs were yellowish, and I thought their decline might be the result of parasitism. Hydnora africana was fruiting abundantly on the roots of one such shrub, and I collected fruits in the hope of cultivating them upon my return, the last week of December, to the United States. Shortly after arrival back in California, I bought several rooted cuttings of Euphorbia caputmedusae in the hope of germinating seeds of the Hydnora the fruits were still in fresh condition and intact. Euphorbia mauritanica is not in cultivation in California, but E. caputmedusae, most commonly cultivated here, was judged suitable because it is the host of a small population of H. africana at Houtbaai on the Cape Peninsula. I tapped the Euphorbia plants from their pots, lined the pots thickly with masses of the seeds, and reinserted the plants so that Euphorbia roots would be in intimate contact with Hydnora seeds. About a year later, I removed the Euphorbia plants, noted no apparent infection, and planted them in a larger ceramic pot. Three years from the time of original sowing, removal of the plants revealed no apparent infection. I assumed I had been unsuccessful, and planted the E. caputmedusae plants in a convenient sunny corner of my garden as a way of using the Euphorbia merely as an ornamental. Early in July 1979, five and one-half years after the attempted inoculation of the Euphorbia plants, I was startled to see a single Hydnora flower emerge from the soil surface.

Field work- Considerable more field work is necessary. These plants are so unusual in being largely subterranean and also seasonal that they are no doubt frequently overlooked. The recent re-discovery of H. triceps, noted above should encourage botanists to be more aware of the possible presence of these plants. Additional, well prepared collections are necessary to determine the extent of variability especially in H. johannis. Many herbarium specimens are little more than shards of unusable material.

Geography- The recent collections of H. johannis from Oman add a tremendous range extension. The vegetation of this region of the Arabian peninsula, however, is strongly linked with the corresponding region of Africa.

Culture- The remarkable success of Carlquist in cultivating H. africana should encourage others to do likewise. To my knowledge, there is no botanical garden in the world which is attempting this.

Hosts- Hosts of all four species are known. In the context of holoparasites, Hydnora appears to be rather advanced in that species are generally host specific. (The exception may be H. esculenta but more data are needed). Two unrelated families are parasitized, the Fabaceae and the Euphorbiaceae and within these two large families parasitism is more or less restricted to only two genera, Acacia and Euphorbia.

Conservation- The status of H. esculenta requires immediate attention. So many of the endemic plants of Madagascar are either extinct or facing extinction that this species, unique within the family, may have met the same fate.

Sub-generic classification- Musselman and Visser (1989) include a classification-sub-generic classification but this need considerable further work before it can be considered meaningful. The typification of H. triceps is discussed above.

Familial relationships- The genetic distance between Prosopanche, restricted to the New World, and Hydnora deserves study. Modern molecular studies of plastids (if present) and other nucleic acid sequencing could be powerful tools in understanding the relationships between these two genera. Such a study of holoparasites would have value in other groups, as well. Most modern systems of phylogeny place the Hydnoraceae close to the Rafflesiaceae. I consider this an error as there is little in common between these two families other than being holoparasites. A relationship with the Aristolochiaceae seems more reasonable considering the inferior ovary, beetle pollination syndrome, and large conspicuous singly borne flowers.

Breeding systems- While floral biology is being studied, we know nothing about the breeding systems of these plants. Part of this is due to the inherent difficulty in simply determining what is a plant! The lack of any fruits in H. triceps is intriguing in this regard. Is it an outcrosser?

Morphology- A thorough study of the development of Hydnora is needed. The early stages of germination have not been described. The monocolpate pollen, unusual in dicotyledons, deserves further analysis. The anatomy of the root and its distinctive budding system should be carefully described.

Uses- The most frequently cited use is eating the fruits. Those who have had the privilege of doing so can readily attest to their delicacy. Several animals eat the vegetative parts. Because of the high tannin content, the plants have been used as an anti-diarrheal medicine and for tanning hides (Musselman and Visser, 1989). Less common but more dramatic uses are elephant and rhinoceros food (Musselman and Visser, 1989)!

Field work in southern Africa was organized by the late J. H.Visser. I have examined material from the following herbaria andwish to thank the curators for arranging visits and/or loans forstudy: BR, C, E, EA, FT, K, L, LE, LISC, M, MO, ODU, P, PRE, RO,S, SRGH, UPS, and WIND.

Burchell, W. J. 1822. Travels in the Interior of Southern Africa. Volume 1. London: Longman, Hurst, Rees, Orme, and Brown. (Reprint by Johnson Reprint, New York. 1967).

Carlquist, S. J. 1965. Island Life. Garden City, NY: The Natural History Press..

1989. Hydnora in my garden! Haustorium, Parasitic Plants Newsletter 21:2-3.

Jones, D. L. 1988. Native Orchids in Australia. Frenchs Forest, NSW: Reed Books.

Musselman, L. J. 1984. Parasitic angiosperms of Sudan: Orobanchaceae, Hydnoraceae, and Cuscuta. Notes Royal Botanic Garden, Edinburgh 42: 21-39.

Musselman, L. J. and J. H. Visser. 1987. Hydnora johannis in southern Africa. Dinteria 19: 77-82.

Musselman, L. J. and J. H. Visser. 1989. Taxonomy and natural history of Hydnora (Hydnoraceae). Aliso 12(2): 317-326.

Nickrent, D. L. and C. R. Franchina. 199. Phylogenetic relationships of the Santalales and relatives. Journal of Molecular Evolution 31: 294-31.

Parker, C. 1988. Parasitic plants in Ethiopia. Walia 11:21-27.

Visser, J. H. 1981. South African Parasitic Flowering Plants. Cape Town: Juta.

Visser, J. H. 1989. Hydnora triceps. The Flowering Plants of Africa 5(2). Pretoria: Department of Agriculture and Water Supply.

Visser, J. H. and L. J. Musselman. 1986. The strangest plant in the world. Veld and Flora. December 1986/January 1987: 19-111.

1. ADAPTED FROM: Musselman, L. J. 1991. The genus Hydnora (Hydnoraceae). pp 247-25 in Ransom, J. K., L. J. Musselman, A. D. Worsham and C. Parker, eds. 1991. Proceedings of the 5th International Symposium of Parasitic Weeds. 55 pp ix. Nairobi: The International Maize and Wheat Improvement Center (CIMMYT).

2. A large project to typify all Linnean specimens is centered at the British Museum (Natural History) under the direction of Dr Charlie Jarvis who asked me to designate a type specimen for the genus. I had examined the type specimen of Hydnora africana in the Thunberg collection at Uppsala (Sweden) and with the help of Dr Mats Thulin have chosen Thunberg 15452 as the type. This sheet (Thunberg 15452) is marked " Capite bonae spei C. P. Thunberg."

How Are Animals Classified?

Biological scientists estimate that collectively the earth’s 5 to 40 million species of organisms (depending on the estimate you choose to believe) make up a total of some two trillion tons of living matter, or biomass. The plants comprise well over 90 percent of the biomass. The animals, the focus of this article, comprise only a small percentage of the biomass, but they account for the majority of species.

In accordance with the Linnaeus method, scientists classify the animals, as they do the plants, on the basis of shared physical characteristics. They place them in a hierarchy of groupings, beginning with the kingdom animalia and proceeding through phyla, classes, orders, families, genera and species. The animal kingdom, similar to the plant kingdom, comprises groups of phyla a phylum (singular for phyla) includes groups of classes a class, groups of orders an order, groups of families a family, groups of genera and a genus (singular of genera), groups of species. As established by Linnaeus, the scientists call an animal species, as they do a plant species, by the name of the genus, capitalized, and the species, uncapitalized. So far, the scientists have classified and named something over a million animal species. Without doubt, they have millions more to go.

Taxonomists, biological scientists who specialize in classifying and naming the living organisms, group the multicellular, independently mobile organisms that eat other organisms into the kingdom of animalia. The taxonomists recognize that the animals, unlike the plants, possess specialized tissues that may be organized into even more specialized organs, and they recognize that most animals, especially the more evolutionarily advanced species, have &ldquobilateral symmetry,&rdquo which means that the right and left sides are essentially mirror images of each other. Critically, especially in the desert, animals, unlike plants, often utilize their mobility to seek refuge from environmental stresses such as intense heat and prolonged drought.

Animal Populations

Worldwide, the animal population consists of species numbering somewhere in the millions. The largest, the blue whale, may exceed 100 feet in length and 150 tons in weight. The smallest known animals, for instance, a parasitic wasp that taxonomists have named Dicopomorpha echmepterygis, measure no more than a few thousands of an inch in length.

The most abundant and diverse animal communities occupy earth&rsquos most biologically productive regions, for example, the tropical rainforests, where the species of living organisms probably number in the millions. Conversely, the least abundant and diverse animal communities live in the least biologically productive regions, in particular, deserts like those of our Southwest, where the species of living organisms likely number in the tens to hundreds of thousands.

The biological richness of a tropical rainforest contrasts sharply with the biological impoverishment of our deserts. The net biological productivity of a typical area in a tropical rainforest may exceed that of a comparable area in our desert lands by a factor of 40 to 50 times, according to the Physical Internet site. Moreover, according to the Tropical Rainforest Biome Internet site, &ldquoScientists believe that the tropical rainforests of the world might hold up to ninety percent of the plant and animal species on earth.&rdquo In a paper called &ldquoTropical Biomes,&rdquo Professor Ralph E. Taggart, Michigan State University, said &ldquoThe total biological diversity of only a few square kilometers of rich tropical rainforest can exceed that of entire regions in the temperate zone. Most of the plants and animals of the world are found in the complex mosaic of natural communities that make up this biome.&rdquo Nevertheless, our deserts host a diverse and highly adapted community of animals.

The Animal Community

Taxonomists typically divide the animal kingdom into two &ldquosubkingdoms,&rdquo which include the invertebrates (animals without backbones) and vertebrates (animals with backbones). As with the plants, taxonomists turn the subsequent animal groupings and classifications, from phyla through genera, into a churning landscape that is simply a part of the scientific process. Depending on their academic roots and research, they divide and re-divide the animal community in many different ways, frequently regrouping, reclassifying and even re-naming species as they go. Some, called &ldquolumpers,&rdquo identify species as belonging to the same group even though there may be small differences. Other scientists, called &ldquosplitters,&rdquo identify the same species as belonging in distinct groups because of the same small differences. The lumpers produce a relatively simple taxonomy, the splitters, a far more complex taxonomy.

Classifying an Invertebrate

In our deserts, the invertebrate subkingdom includes phyla such as arthropods (insects, centipedes, spiders, scorpions, desert shrimp and many others), mollusks (snails) and annelids (earthworms). In the desert, as well as across the world, arthropods, measured in terms of abundance and diversity, rank at the top of all the animal phyla. An elegant insect, the monarch butterfly, serves as example of how the classification system works for the invertebrates.

At the phylum level, the monarch belongs to the arthropods, which share several physical characteristics. According to Barbara Terkanian, &ldquoA Vertebrate Looks At Arthropods,&rdquo A Natural History of the Sonoran Desert, the arthropods have jointed legs, and they have external skeletons, or exoskeletal material, that includes &ldquoeyes, mouthparts, antennae, body, legs, the fore and hind sections of the digestive tract, and some respiratory surfaces. Regions of flexible, unhardened exoskeleton serve as joints between neighboring segments.&rdquo The body cavity contains the digestive, circulatory, nervous and reproductive systems.

At the class level, the monarch has membership in the insect group, which comprises the overwhelming majority of the arthropods. The insects have several distinguishing physical characteristics, including three-part bodies, six legs (three pairs), compound eyes and two antennae. The class, called Insecta, includes three subclasses, according to Kendall Bioresearch Services Internet site. The first consists of insects that have never had wings throughout their evolutionary history. The young resemble the adults. The second subclass consists of insects that have wings at present or had them at some point during their evolutionary history. The nymphs resemble the adults. The third subclass consists of insects that have wings at present or had them at some point during their evolutionary history. The young take the form of larvae that change into adults during a non-feeding metamorphosis. The first subclass consists of four orders, including, for example, bristletails and springs tails. The second subclass has 16 orders, including, for instance, dragonflies crickets, grasshoppers and locusts termites and sucking lice. The third subclass has nine orders, comprising insects such as beetles fleas bees, wasps and ants and the butterflies and moths.

At the order level, the monarch belongs to butterflies and moths, called Lepidoptera, which rank high among the most intriguing and conspicuous insect orders in the Southwest. They have two pairs of membranous, scaled and often brightly colored wings. Typically they have large eyes, long antennae and a long sucking tube (which the insect coils beneath its head when not feeding). The larvae, or caterpillars, all have silk glands that they use for spinning their cocoons. Their order contains well over 100 families.

At the family level, the monarch is the star of the milkweed butterflies, called Danaidae, which are among the best known in our deserts (as well as across the country). The milkweed butterflies usually have goldish wings trimmed in black, according to Donald J. Borror and Richard E. White, A Field Guide to the Insects of America North of Mexico. Their caterpillars feed on milkweed leaves, which invest both larvae and adults with a bitter and toxic taste that discourages predators.

At the genera level, the monarch is one of a mere handful of closely related species collectively called Dannaus. These species show apparently common evolutionary origins in their caterpillars, which share similar spots and smooth skin texture on their abdomens, according to David Munro, &ldquoThe Biogeography of the monarch Butterfly,&rdquo San Francisco State University, Department of Geology, fall 1999.

At the species level, the monarch is called plexippus. It is, says Munro, &ldquoa medium sized butterfly, measuring about 3 inches from wingtip to wingtip. Its body is about one inch long. Its four wings are generally a field of yellow, orange or gold, with veins of black running through them. A band of black, thickest at the front, rings the wings, and the body is black as well. This black band is usually speckled with white spots, larger at the front and smaller at the back.&rdquo

The monarch, the aristocrat of the butterfly and moth world, bears the scientific name of Dannaus plexippus. In summary, it fits into the Linnaeus classification scheme as follows:


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