Species and varieties, bulbs and trees

Joe Shaw jshaw@opuntiads.com
Fri, 08 Jun 2007 12:18:00 PDT
Hi Gang,

We've had some very fun and useful discussions in this forum about taxonomy, 
species, subspecies, varieties, and how to distinguish between all the 
possibilities.  Bulbs are sometimes just as confusing as any other plants, 
and because they may come from far away, or be garden hybrids, bulbs can be 
very mystifying to some of us as taxonomic entities.

I was reading a book recently that had a nice map of the distribution of 
redbud in Texas (Cercis canadensis).  This tree is generally accepted to be 
represented by 3 varieties in Texas (var. canadensis, var. texensis, and 
var. mexicana).  I colored a map of Texas to reproduce the data in the book 
(Field Guide to Trees of Texas, B. Simpson, 1999).  His map shows the 3 
varieties and how they are distributed over Texas counties.  Additionally, 
the book depicts two hybrid swams and the counties where they occur.  The 
hybrid swarms are populations of plants that are intermediate, the plants 
have inconsistent morphology or habits and may represent one variety more 
than another, or can be equal admixtures.

LINK:  Distribution of Redbud (Cercis canadensis) Varieties in Texas

The really interesting thing is that one hybrid swarm (D) appears not to 
mark the boundary between two varieties (at least in Texas).  Rather this 
swarm (mixture of var. mexicana and var. texensis) is like a spur driving 
north out of Mexico.  The distribution is interesting because it splits var. 
texensis into to disjunct populations within the state of Texas.  See the 
map, magenta counties (labeled "D").

Back to bulbs:  hybrid swarms are common in nature.  Species are real, and 
do occur, but they are unpredictable and need not be spread out in a 
geographically "logical" manner.  Hybrid swarms may be clines (and so 
represnet a gradual change of characteristics over distance), but swarms can 
also be a confusion, a mix of features.

From all of this I infer that field botanists and ecologists, those who 
laboriously study plants in Nature, county by county and field by field, are 
true heroes in helping us understand plant species and their endless 
varieties and distributions.  I think geophytes can present especially 
challenging objects of study because they may only be above ground a few 
weeks each year, or every other year, and they may have ephemeral flowers. 
A visit to a locality might not reveal the presence of any plants, yet a 
visit two months later could uncover vast populations (e.g., Herbertia lahue 
in Texas).


Conroe TX

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