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Re: SPEC: X robusta


In a message dated 98-06-02 01:44:10 EDT, you write:

<< This is what is said in the '89 checklist:  GERALD DARBY (G. Darby by coe,
R. 1968). Change of classification, description  and parentage to: LAEV apogon
hybrid, up to 6' (183 cm). Blue violet with  violet-colored leaf bases.
Appears to belong to I. x robusta, E. Anderson, the  cross of I. versicolor
with I. virginica. Sets few good seeds. Chromosome  count 2n + 88-89.

 Maybe someone can shed some light about what I. x robusta really means?  >>

I'll take a whack at this. Someone more knowledgeable will correct me if I err
or miss the fine points, but I'll take a preliminary whack at it for you,
Sterling. The simple explanation is that this plant is an interspecific cross
between members of the genus Iris.This is indicated by the "X". That is, it is
a hybrid species, a probable cross between I. versicolor and I. virginica.  

So reading the Checklist across we see that the classification of the plant,
as based on its parentage, is being corrected to indicate that it is a
beardless hybrid of the Laevagatae, and that it is (now) thought to be a named
clone of I.x.robusta as named by E. Anderson. Now, I don't know the full story
on the delimitation of this category I.x robusta, but I will quote from the
BIS book, A Guide to Species Irises: Their Identification and Cultivation, on
p. 8f. The issue under discussion there is the utility of chromosome counts
for botanical classification purposes and the author is making his point by
using a population of wild blue flags in northern England as an example. He
says that they:

"...could casually be assumed to be I. versicolor on the basis of floral
morphology, but chromosomally  this popluation is distinctive in having a
somatic chromosome number of 2n=89....This chromosome number strongly suggests
that the popluation represents a hybrid between I. virginica (2n=70) and I.
versicolor (2n=108) and the high sterility of the plants supports this
suggestion. Such hybrids are common in the USA where the two species overlap
and where the hybrids have been given the binomial I.x.robusta (Anderson,
1928)." 

Hope this helps.

Anner Whitehead, Richmond,Va
Henry Hall, Henryanner@aol.com










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