how many differences for a species?

D. Christopher Rogers
Mon, 23 Oct 2006 08:45:19 PDT
Dear Diana,

I am a professional taxonomist, however I work with crustaceans not plants.
In zoology, the genus concept has become formally defined as a group of
species where hybridization is possible: i.e., a zygote can be formed
regardless of whether the parents are actually capable of mating. In my
crustaceans, genera are defined by the basic form of the male and female
genitalia; characters that are highly conserved in evolution because they
are governed mostly by sexual selection. If the animals cannot reproduce,
there are no genes to be passed on. At the species level, the crustaceans
that I study are separated based on the form of the male second antennae,
which are used to amplex the female prior to copulation. Again, these
characters are primarily formed through sexual selection. What it often
comes down to is that species are typically defined by what the animal
recognizes as a potential mate.

When I (or any taxonomist) finds what I think is a new species, I write up a
paper describing it, deposit type specimens at one or more international
museums, and submit the paper to a scientific journal. At the journal, the
paper is sent to three or more independent reviewers, (hopefully) people who
also are familiar with the taxonomic group that the new species is in. These
reviewers may have many questions or comments, or may wish to examine the
material that I deposited in the museums before reviewing my paper. After
review and edits, if the paper is good, it is published, and the new taxon
is valid.

I am often amazed at botanical taxonomy. There do not appear to be any
quantitative definitions for most taxa. So many species defined by such
small and often qualitative characters. If hybridizability were a criterion
for plant genera, then nearly all of the thousands of orchids would be in
one mega-genus! Conversely, polyploidy (extra sets of genes) often causes
plants to be unable to hybridize, so then how could two morphologically
identical plants, one a polyploid, be separate genera?

I hope this in some way is helpful,

D. Christopher Rogers
Invertebrate Ecologist/Taxonomist

EcoAnalysts, Inc.
(530) 406-1178
166 Buckeye Street
Woodland CA 95695 USA

? Invertebrate Taxonomy
? Invertebrate Ecological Studies
? Bioassessment and Study Design
? Endangered Invertebrate Species
? Zooplankton
? Periphyton/ Phytoplankton

Moscow, ID ? Bozeman, MT ? Woodland, CA ? Neosho, MO ? Selinsgrove, PA

-----Original Message-----
From: []On
Behalf Of Diane Whitehead
Sent: Sunday, October 22, 2006 10:32 AM
To: Pacific Bulb Society
Subject: [pbs] how many differences for a species?

I have heard it said that a different colour should not mean a new
species. OK, that makes sense.  However, upon reading descriptions of
several species of Hesperantha, I wonder how many differences are
required for a different species.

Here are a couple of examples of species with several differences.

Hesperantha falcata  is either white, scented, evening-flowering  or
yellow, unscented, midday flowering.

Hesperantha pilosa  is either white, scented, evening-flowering or
blue to purple, unscented, day-flowering.

Has anyone grown both kinds of either of these, and would you have
thought they were the same species if the labels didn't say so?

                        Diane Whitehead

pbs mailing list

More information about the pbs mailing list