With permission granted to collect just a few more samples, I went back to the iris sites and got two capsules. Each one appeared to be ripe. Took them home, opened them up, photographed them…

And damn if I still haven’t reached a conclusion.

According to the Flora of North America, Iris virginica has

Seeds in 2 rows per locule, pale brown, usually D-shaped, 5–8 mm, pitted, corky. 2n = 70, 72.

while Iris versicolor has

Seeds dark brown, D-shaped, 5–8 mm, shiny, thin, hard, regularly pebbled, not corky. 2n = 108.

How would you describe these seeds?

Once again I sought expert advice, this time from the Species Iris Group of North America and an iris-specific internet forum. One kind gentleman wrote to me:

Elizabeth Miller, please see the paper attached below. Iris virginica is 2N = 70 Iris versicolor is 2N = 108, it is an allopolyploid stable hybrid of Iris virginica and Iris setosa (2N = 38) which occurred post glaciation after the Laurentide Ice Sheet shifted a population (dramatically) from Western North America all the way across to the East, into the range of Iris virginica. Since you have a permit for collection, you may wish to contact your nearest university with a Hort program and see if they can do an analysis. In general from a phenotypic perspective Iris versicolor has short standards, which it inherits from Iris setosa, which has bristle like almost invisible standards. But Iris virginica phenotypes are variable and some occasionally have a shorter or rounder standard. So it is best, and most accurate, to go with a chromosome analysis:
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2735315/

[Parental Origin and Genome Evolution in the Allopolyploid Iris versicolor]

I was also pointed to the classic article “The Problem of Species in the Northern Blue Flags, Iris versicolor L. and Iris virginica L.”, by Edgar Anderson, originally published in Annals of the Missouri Botanical Garden [Vol. 15, #3, Sept. 1928].

The article was fascinating, and I’ve been struggling to come up with a way to briefly summarize it while doing justice to the detail. If you’re interested in such things, it’s worth getting a (free) jstor account.

After introductory remarks and descriptions of the species, the author presents a chart of “Comparative Morphology”, followed by some interesting observations:

Wherever either species was studied, the individual plants which went to make up a colony were found to vary strikingly among themselves. They varied in every conceivable characteristic, both vegetative and floral… The flowers varied in size and form, in color and color pattern, in number and arrangement, in texture…

…It is thus apparent at the outset that no biometric method of distinguishing the two species can be a simple matter.

That made me feel better about my own failed attempts. It also made me wonder if I wasn’t right in thinking that the lumpers should have won this round. But earlier in the paper, Anderson writes

It has been found that what commonly passes for Iris versicolor L. is made up of two species… the species are wholly distinct and crosses between them are partially sterile.

So I kept reading, only to discover that after detailed analysis of numerous specimens, Anderson discards mathematical models and comes up with a fascinating method of comparing specimens by creating ideographs based on groups of characteristics. After comparing ideographs, Anderson concludes

In marked contrast to the variation between individuals is the general resemblance between colonies of the same species.

And

Above all, when the ideographs are considered as a whole, the two species remain completely and absolutely distinct. In spite of a wide range of variation in separate characteristics, when the combination as a whole is studied it is found to be strikingly constant. Iris versicolor remains always and unmistakably Iris versicolor, and Iris virginica remains always and unmistakably Iris virginica. There is not the slightest tendency to one species to merge into the other.

So where does all this leave me? I can’t create the ideographs without access to a large number of specimens – quite possibly more than either stand of irises affords. Which leaves chromosome analysis.

And that’s where I draw the line. Even though a botanist friend has promised use of her microscope so I can do it the “old-school way”, should I be able to collect samples of root tissue.