In a Class by Themselves?

This article originally appeared in the Aril Society International Yearbook, 1993.


Classifying garden plants is not easy. Botanists encounter tremendous difficulty in classifying wild plants, and these problems are only compounded when it comes to garden hybrids. Common sense dictates that we should group together plants with similar appearance, similar manner of growth and similar origin. The gardener might add that plants with similar uses in the garden should also be grouped together.

Horticultural classification

In genera such as Iris, where there is great diversity even in the wild, and where many species hybridize readily, plant specialists often make use of a horticultural classification system, which groups plants simply by their visible characteristics and growth habits, and which does not attempt to unravel their genetic history or relate them to well-defined species. The system used by the American Iris Society to classify the bearded irises is an example of such a horticultural classification. The dwarf, median, and tall bearded irises are sorted into six classes based on various horticultural criteria: height, season of bloom, and proportion. The classification system certainly reflects the genetic background of the plants; MTBs traditionally come from diploid tall bearded breeding, BBs from tetraploid tall bearded breeding and lBs from crossing tall beardeds with SDBs. However, the inventors of the system recognized that there is a great diversity in both the ancestry of the medians and in their resulting plant qualities. Hence, parentage and genetic makeup are not defining characteristics for any of these classes. That is why we now have tetraploid MTBs and lBs descended from Iris aphylla that are genetically similar to the BBs and TBs. They are classified as MTBs and lBs not because of their ancestry, but because that is where they belong horticulturally, in terms of size, shape, season, and garden uses.

Classification by ancestry

In contrast, the ASI now classifies arils and arilbreds based strictly on ancestry. Furthermore, the classification of arilbreds uses only the type and quantity of aril ancestry; what types of bearded irises appear in the pedigree is not considered important.

For example, suppose you managed to cross 'Esther the Queen' (1/2 aril) with your neighbor's orange tomcat. The progeny, bearded or bewhiskered, would presumably plant itself next to the catnip bush and require frequent side dressings of fertilizer and kitty litter. Although this strange creature would be quite unlike any other arilbred, under the ASI classification it would certainly be an OGB-, eligible for the William Mohr medal. By ancestry, it is one quarter aril and three quarters "other."

This ludicrous example is intended to illustrate one of the advantages of a horticultural classification system: it tells gardeners what to expect, better than does a system based on ancestry. This makes horticultural classification systems useful tools for promoting new plants to the gardening public.

Horticultural classification for arils and arilbreds

If the arils and arilbreds were to be classified by a horticultural system, how would it work? It would have to group together plants with similar cultural requirements, similar flower characteristics, similar overall size, and similar season of bloom. A first cut at such a system might look something like this:

ARILS (AR): small to medium plants, dormant in summer, with one or two blooms per stalk; most are dramatically marked with veining, dots, or signals. Flower form is often distinctive, either globular or angular. Most bloom very early. Examples: 'Babylonian Brass', 'Artemis', 'Persian Pansy'.

ARILBREDS (AB): medium to tall plants, green or semi-dormant in summer, with two to four blooms per stalk; flowers showing aril characteristics, but form usually less extreme. Most bloom early, before tall bearded season. Examples: 'Big Black Bumblebee', 'Esther the Queen', 'Persian Padishah'.

QUARTERBREDS (ABQ): plants resembling tall beardeds, but displaying some distinguishing aril characteristic(s) such as veining, somewhat globular form, early bloom season, or limited branching. Examples: 'Dune', 'Desert Solitude', 'Engraved'.

ARILBRED MEDIANS (ABM): medium sized plants, resembling lBs in bloom season, growth, and overall proportion, but exhibiting some aril characteristics. Examples: 'Fairy Goblin', 'Omar's Torch', 'Cairo Love Song'.

ARILBRED DWARFS (ABD): small plants, resembling SDBs or MDBs in bloom season, growth, and overall proportion, but exhibiting some aril characteristics. Examples: 'Tiny Tyke', 'Barbarella', 'Nightlight'.

Ancestry would not be a defining characteristic for these classes, but among today's cultivars, most ARs derive from oncocyclus and regelia species, most ABs and ABQs are from arils and tall beardeds (the ABQs generally from AB x TB breeding), and most ABMs and ABDs are from mixed aril, dwarf bearded, and tall bearded ancestry (the ABDs having less TB ancestry or none at all).

Such a system would be useful for promoting aril and arilbred irises. The ABM and ABD classes, in particular, establish important distinctions for the gardener. Iris hobbyists and commercial growers already recognize this, segregating out the small arilbreds with dwarf ancestry, calling them "arilmeds," "arilmedes," "arilmedians," and other similar terms. As useful as these designations are, they lack any official ASI or AIS endorsement.

Fifteen years ago, I might have argued for such a horticultural classification system to promote the arilbred medians. Now, these small arilbreds seem to have quite overtaken the quarterbreds in popularity. Today, it seems to be the quarterbreds and arilbred dwarfs that would benefit by being in classes by themselves.

The quarterbreds are unfairly maligned. Aril specialists are often frustrated by the quarterbreds having few aril characteristics, while TB growers ignore them because of the prejudice that arilbreds are difficult to grow. Many quarterbreds make attractive specimen plants in the garden. The better ones have large and colorful blooms, providing more drama than a typical TB.

The distinction between ABMs and ABDs may not seem necessary, but I believe it is. Not only do the miniatures occupy a different niche in the gardener's plans, they may soon become much more prevalent. Now that tetraploid arils are easily available, we can expect a new fertile family of arilbred dwarfs to emerge from crossing the tetraploid arils with Iris pumila. This development is comparable to the creation of the fertile family of tall arilbreds by C. G. White half a century ago.

Although a horticultural classification system does not assign plants to classes on the basis of ancestry, a plant's garden qualities are certainly expressions of its genes. Most plants from similar breeding will fall naturally into the same class. The triangle diagram illustrates the relationship between ancestry and horticultural class. Ancestry can be aril, tall bearded, or dwarf bearded. The amount of each type of ancestry can be none, 1/4, 1/2, 3/4, or all. If the plants are tetraploid, these steps correspond to complete chromosome sets. Classes that currently contain few or no plants are shaded.

Proposals for alternative classification systems often create a great deal of controversy, especially when they impact the scope of the various plant societies and awards. Much debate revolves around the number of plants introduced in each class and the appropriateness of separate awards for them. I believe these considerations should be secondary, the primary purpose of a classification scheme should be to serve the needs of those who use it. I think gardeners and iris hobbyists would be well served by a horticultural classification of the arils and arilbreds, as outlined in this article.


I have recently discovered that Walter Welch had argued strongly for a horticultural classification of arilbreds. The following is an excerpt from his "Thoughts on Classification," which appeared in the 1967 ASI Yearbook.

"Looking into the future, with this prospect, we can now see other problems of classification coming up. You will probably in time have dwarf, median, and regular tall arilbreds as different classes, and each will require separate identification marks to distinguish them. But once you have determined the main course of an arilbred classification, it should not require too many further additions to distinguish between the various kinds or class types. No doubt the matter of size will be a consideration, or perhaps season, or possibly some other character deriving from the bearded parent could be worked into this category.

"I don't think I can add much to the above comments as regards classification for [the ASI]. But I do think you are all working on a wrong basis by this percentage or parentage computation. So my suggestion is to get busy working out a classification based entirely on how the plant looks, its visible characteristics, and make it so obvious that the ordinary member with just a minimum amount of knowledge can stand before the iris and say that has onco or regelia blood in it, it is an oncobred or a regeliabred. That is not just an idea, it is a must, and the quicker you recognize it the sooner your troubles will be solved."

 Tom Waters

March 2011

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Unless otherwise noted, all text and illustrations copyright Tom Waters and all photographs copyright Tom or Karen Waters. Please do not reproduce without permission.