Monday, February 7, 2022

The Iris X-Files

by Bob Pries

Botanical names for hybrid irises are written Iris x species. They have more in common with the TV program X-Files than just the X. The television series dealt with FBI agent Molder investigating files that the department did not wish to touch, because they contained paranormal phenomena that could destroy the reputations of serious investigators. The botanical “X-files” have the same danger. In this regard it probably puts my credibility at risk to discuss my collection of “X-files,” but here goes.

The Kew Checklist of Botanical Names lists almost 200 hybrid binomials. For your consideration I have compiled a list, here, in the Iris Encyclopedia under “Botanical Nomenclature for Hybrids.” On inspection there are several that are relegated to just a few synonyms and these have interesting back stories.

Iris x violipurpurea and Iris x vinicolor

The first group I will mention brought about the fall of a giant in botany at the time. John Kunkel Small was a celebrated botanist. He had completed a flora of the Eastern United States and easily knew more about its flora than anyone else. The herculean task he accomplished cannot be denied. But he took a fateful train ride into the swamps of Louisiana. Looking out the window he saw scores of irises like he had never seen. He came back and collected a truckload that was sent back to the New York Botanical Garden to be grown and studied. He and his colleague Edward Johnston Alexander ultimately published a paper proclaiming about 110 species of irises in the Southern United States.

Iris brevicaulis, Iris giganticaerulea, and Iris fulva, the three parental species of Iris x volipurpurea

The botanical world was shocked! It was soon demonstrated by Percy Viosca that most of these irises were not new species but hybrids of Iris fulva, Iris giganticaerulea, and Iris brevicaulis.  The Kew lists reflects this by changing 61 of these names to hybrid names rather than accepting them, except as synonyms of one master name for this parentage of three parent species (Iris x violipurpurea). One other hybrid name was accepted as the name for just Iris fulva and giganticaerulea crosses (Iris x vinicolor).  So all of those names that Small thought were different enough to be separate species, were essentially lost. But this diversity could still be recognized as cultivar names.

Iris x volipurpurea "cultivars" 'Chrysophoenicia' and 'Chrysaeola' are similar to about 60 others that were originally considered species but were later classified as hybrids

Horticulturalists often complain about how botanical names continually change. This is because they denote evolutionary relationships. As the understanding of these relationships changes, so do the names. Horticultural ‘cultivar’ names are meant only to distinguish the types of plants and are usually unchanging. So these rejected species of Small became cultivars such as ‘Aurilinea’, ‘Chrysophoenicia’ and ‘Rosipurpurea’ etc. and were published as such in the 1939 American Iris Society Alphabetical Iris Check List. (The rule that cultivars could not have Latin names came later.) These cultivar names replace the botanical hybrid names.

Of course, when the world reacts it often overreacts. Viosca admitted that he was only referring to the irises that Small named in Louisiana. But many botanists immediately assumed that the irises that Small described from Florida were also hybrids. Dr. Phil Ogilvie championed more investigation into these irises and pointed out that each seemed to be relegated to its own river system in Florida. Henderson recognized Iris savannarum from Florida in The Flora of North American and relegated those other species as synonyms of savannarum. Today some botanists take an extreme view that all these irises are examples of the same species using the name Iris hexagona. So the pendulum swings.

Even botanists using some modern techniques claim Iris nelsoni as nothing but a hybrid Iris x nelsoni. But this stance puts a very rare group of irises from around the Abbeville, Louisiana area at greater risk because how much support can you gather to protect a hybrid versus a species? No one contests that in the past it developed as a hybrid from Iris fulva; but its ecological requirements today are very different, and it certainly plays a different role in the ecosystem. Other species have been shown to have been developed through hybridization, such as Iris versicolor from Iris setosa and Iris virginica.

Iris pallida and Iris variegata the two species that were parents of diploid tall-bearded "species"

Iris x amoena and Iris x squalens two irises resulting from the above cross

Another big group of botanical hybrid names (55) are those relegated to synonymy with Iris x germanica. Sir Michael Foster convincingly showed that a number of diploid tall bearded iris that had previously been called species probably formed as the result of the two diploid species Iris pallida and Iris variegata. The Kew Checklist gives Iris x germanica as the hybrid name for this parentage. When one sees Iris x squalens, Iris x amoena, Iris x neglecta, etc. This seems perfectly reasonable. But there are two other groups that do not fit well in this hypothesis.

“Grandma's Old Blue Iris” a sterile triploid

First is the iris that is widely grown and called Iris germanica. Unfortunately it has no other name to distinguish it except “Grandmas Old Blue Iris” It is often referred to as triploid, and seems totally sterile. Unlike the other “Germanicas” it is an intermediate iris. It is said to have 44 chromosomes. Pallida and Variegata have 24 chromosomes. Many believe it is the product of a 40-chromosome parent (20 chromosome gamete) and a 24-chromosome parent with an unreduced gamete. Iris albicans and Iris florentina share a similar type of background, and are sterile; but presumably come each from a different 40-chromosome parent.

The other group being referred to Iris x germanica are presumably 48-chromosome tall bearded irises. Murray was troubled by the fact that modern tall bearded irises were tetraploid while the earlier TBs were diploid so he proposed a new name Iris x altobarbata, which in Latin means tall-bearded. The Kew Checklist does not accept this name probably on a procedural technicality. Another attempt to name the tetraploid “germanicas” was made by Henderson with his Iris x conglomerata (a name not mentioned in the Kew list. Henderson’s argument was that many species have gone into the TBs including Iris pumila, hence the conglomerate. This name did not follow all the rules of publication.

'Amas', a tetraploid I. germanica

Despite two attempts, no satisfactory name has emerged for this group.  I have yet to see strong evidence that the tetraploids emerged from the combination of Iris pallida and Iris variegata which is how I. x germanica is being defined. There have been several “species” that have been defined as I. germanica. One of the key iris to be added to the pallida/variegata mix that precipitated tetraploid offspring was ‘Amas’ which is probably best viewed as a cultivar. Itself of hybrid origin it did not produce pods but its pollen changed the face of tall-bearded irises by fathering the new tetraploid I. germanica cultivars.

There are a number of irises that were essentially cultivars, and expressed here as botanical hybrids but could be candidates for the name of the 48-chromosome species that are relegated to Iris x germanica if one does not buy into the parentage as resulting from the two diploids  I. pallida and I. variegata.

Like the X-files of TV, the data can be debated. I have just pointed out two botanical hybrid names (Iris x germanica and Iris x violipurpurea) that account for half of the list of 200. There are still many x-names that function admirably to identify groups that originate from a given set of species. And there are also many more that have not been included in the list. But perusing what is listed may widen ones knowledge of various lineages. As agent Molder would say “The truth is out there.” Take a look at the X-Files, here.

1 comment:

  1. In other plant genera I grow, there is no taxonomical distinction between diploid, triploid and tetraploid forms of a species or nothospecies (e.g. Liliums, for which several species have been found as both diploid and triploid, or orchids, for which ploidy does not change the grex name). In my opinion this is the correct approach - a tetraploid form of the same nothospecies does not warrant a different taxon to the diploid form.