Using Species in MDB Breeding, Part 1: Iris lutescens

by Tom Waters

I’m a hobby hybridizer, working on a very small scale (I can only raise about 200 seedlings each year). So from the outset, I planned to focus on niche projects, rather than trying to compete with the large-scale hybridizers and their well-established breeding lines. I identified some projects that I thought might have value, but that few others were working on. One of these is to develop a line of true-breeding miniature dwarf bearded (MDB) irises.

As I’ve written previously, most MDBs produced today are small selections from standard dwarf bearded (SDB) breeding. Because the lines of the top SDB hybridizers are so advanced, this approach indeed produces many fine MDBs that display all the variety of color and refinement of form found in the modern SDBs. With a few exceptions, however, hybridizers do not have dedicated lines aimed specifically at producing MDBs. Rather, they select them from among their SDB seedlings that happen to fall below the height limit separating the two classes. Since these plants are genetically no different from SDBs, they are likely to produce SDB-sized seedlings, and some are prone to growing out of class, showing foliage and stalks out of proportion to their size, or having flowers that are too large and coarse.

In earlier times, most MDBs were produced by crossing SDBs with the species Iris pumila, which indeed produced smaller, daintier plants than those from pure SDB breeding. Unfortunately, these plants are unbalanced tetraploids with limited fertility, making them dead-ends.

If one is seeking a true-breeding line of MDBs, there are several options. One is to start with the SDBs and keep selecting for smaller size. Another option is that promoted by Ben Hager: cross tetraploid MTBs with I. pumila, then cross those seedlings with small SDBs or MDBs from SDB breeding. The idea here is that the MTB X pumila crosses will produce genetically smaller plants, and the genes for small size can be stabilized in the breeding line.

A third approach, which I have been exploring, is to expand the gene pool by using species (or combinations of species) that are small in size but belong to the same fertile family as the SDBs. This not only has the potential of creating a line of true-breeding MDBs, but also increases genetic diversity, which may give more variety of forms and colors. This is the first of a series of posts on this project, focused specifically on my hybridizing with I. lutescens and its close relations.

I. lutescens is a dwarf species found in the Mediterranean lands of southwestern Europe, particularly Spain, France, and Italy. There are many related but different populations in this range, which are sometimes given species status, but more often treated as synonyms of I. lutescens. I. subbiflora in Portugal and I. bicapitata in Italy, are almost always treated as separate species, but are part of the same continuum of types found in I. lutescens. Before the 1950s, most dwarf irises found in gardens in western Europe and North American were forms or hybrids of I. lutescens. After the first SDBs were produced, hybridizers quickly abandoned the older I. lutescens dwarfs in favor of the SDBs, which showed wider color possibilities and improved form.

Given this history, I did not at first think of using I. lutescens in my own hybridizing projects. On reflection, however, it seemed that those hybridizers of the 1950s, ‘60s, and ‘70s were excited about exploring the potential of the new SDBs, and not really concerned with creating true-breeding MDB lines. I. lutescens might indeed still have something to offer toward that goal. In nature, its forms span the MDB and SDB height ranges, and flowers are smaller than those of typical SDBs.

S004-01,
I. subbiflora ex Spain
(SIGNA seed)

 

S019-01,
I. lutescens (SRGC seed)

Early on, I grew a plant of I. subbiflora obtained from the SIGNA seed exchange, collected in Spain. Apparently this raises some doubts about its identification, as there is some question whether there are populations of I. subbiflora in Spain, or only I. lutescens. My plant is not as tall as most descriptions and photographs of I. subbiflora, normally being about nine inches in my garden.

Crossing the subbiflora with SDB ‘Kaching’ (Black, 2009) produced a lot of deep red seedlings, mostly of small SDB size, although height varied from year to year and with location in the garden. Although I enjoyed these seedlings, they were larger than what I was aiming for; so I made an effort to use MDBs, rather than SDBs, in future crosses, and to seek out small plants of I. lutescens to use instead of this I. subbiflora. A cross of I. subbiflora with MDB ‘Circa’ (Johnson, 2015) produced attractive plants near the MDB height limit, but still not as small and delicate as I would like.

S027-07,
'Kaching' X S004-01

 

S044-04,
'Circa' X S004-01

I raised a small purple I. lutescens from seed from the Scottish Rock Garden Club (SRGC) seed exchange. It’s about half the size of the I. subbiflora plant. Crossing this with MDB ‘Miniseries’ (Keppel, 2011) gave me a couple promising seedlings: one with small reddish flowers have rather tall stems; the other has mid-sized purplish flowers on shorter stems. I’d be happier if I’d gotten the small reddish flowers on the small stems! But these are interesting, and I will continue working with them.

S039-02,
S019-01 X 'Miniseries'

 

S039-03,
S019-01 X 'Miniseries'

I also crossed the SRGC I. lutescens with MDB ‘Pearly Whites’ (Black, 2014) and MDB ‘Beetlejuice’ (Black, 2013); and a number of these seedlings bloomed this spring. They were all interesting to look at, mostly nicer in form than expected. It’s too early to be sure what height they will settle out at, but this year most of them looked more like small SDBs than like MDBs.

S055-05,
'Beetlejuice' X S019-01

  

S055-11,
'Beetlejuice' X S019-01

S056-01,
'Pearly Whites' X S019-01

I acquired some other small lutescens plants to work with: one from the Berkeley Botanical Garden, and one from Sean Zera, raised from SIGNA seed. I have not yet bloomed seedlings from these. I keep acquiring more I. lutescens seeds, hoping to expand my collection, particularly in colors other than purple. I. lutescens grows here, but doesn’t seem really happy. My high desert zone 5/6 garden in New Mexico is a long way from the south of France.

I am enjoying working with species in MDB breeding, but it must be emphasized that this is a long-term project. Any use of species in breeding must be followed up with several generations of crossing back to modern hybrids if one wishes to meet current expectations of width, ruffling, and substance. It appears that some persistence will be needed to combine the genes for short stems, small flowers, and narrow foliage in the same line. Still, I’m finding these explorations to be a very satisfying use of my small space and limited resources.

Understanding the Historic Dwarf Bearded (DB) Class

By Tom Waters

Before 1958, the now familiar American Iris Society (AIS) horticultural classes for bearded irises did not exist. Certainly there were bearded irises of different sizes, but the precisely defined “dwarf,” “median,” and “tall” bearded classes were still gradually taking shape as a way to describing the diversity of the bearded irises in nature and in the garden. Today, we use “median” to refer to all the bearded irises except miniature dwarfs and tall bearded. 

Consequently, care must be taken in assessing how the earlier bearded irises were categorized. This post will look at just one such category, the dwarf bearded irises, abbreviated DB prior to 1958.

DB 'Artoviolacea' (Todaro, 1856)
probably a natural hybrid
of I. lutescens and I. pumila
Photo: El Hutchison

In the early 1900s, botanists were aware of a number of dwarf bearded species, notably Iris pumila, I. lutescens (then mostly known by the name I. chamaeiris), I. aphylla, I. reichenbachii, and others. Gardeners in western Europe and the United States were also familiar with garden cultivars of dwarf bearded irises. These were almost exclusively forms of I. lutescens or hybrids between I. lutescens and other dwarf species. I. lutescens is native to the Mediterranean regions of France, Italy, and Spain. Other dwarf Iris species are native to Eastern Europe, and thus I. lutescens was more accessible to early commercial nurseries in France, England, Germany, and the Netherlands.

There was little concern about establishing a precise definition for the DB category. Dwarf cultivars being grown were easy to distinguish from tall beardeds (TBs), and that was really all that mattered. Crossing dwarfs with talls produced intermediates,  another widely used term. The intermediate beardeds (IBs) were a pretty obvious group of hybrids and easily distinguished from both dwarfs and talls. Keep in mind that this was long before separate awards were established for different irises. Terms like dwarf, intermediate, and tall were helpful descriptions for irises rather than a specific horticultural class that needed to be assigned unambiguously.

DB 'Bride' (Caparne, 1901)
probably pure I. lutescens,
6 to 8 inches in the author's garden
photo: Tom Waters

The AIS checklists of the 1920s defined dwarf bearded irises by listing some familiar dwarf species, and noting that the term included hybrids between these species. The 1939 checklist added some precision by stating that dwarf irises were up to 17 inches in height. It was not clear whether ancestry from dwarf species or height was to be decisive; it was just taken for granted that hybrids among the dwarf species and cultivars would fall into the expected height range.

What were these early dwarfs like? Like the species I. lutescens that dominated their ancestry, the early dwarfs were mostly between 6 and 12 inches in height, almost never branched, bearing one or two terminal buds. Colors ranged from yellow, cream, and white, to blue, violet, and purple. Most had self or bitone color patterns. The spot pattern from I. pumila, so familiar to us in modern dwarfs, was seen only occasionally. All blooms were tailored, and the plants bloomed before the intermediates and talls. Although I. lutescens in the wild often shows interesting markings, patterns, and blended colors, these were not common among garden varieties. Perhaps this reflects the preference for clear, smooth colors that persisted among iris fanciers until the later decades of the 20th century.

DB 'Path of Gold' (Hodson, 1941),
a child of 'Bride' and
probably pure I. lutescens, is
10-12 inches in the author's garden.
Photo: TomWaters

Hybridizing with dwarf irises took a back seat to TB hybridizing until the 1940s and 1950s. William J. Caparne of England produced many dwarfs around 1900, as did the German firm of Goos and Koenemann. A number of American hybridizers subsequently worked with dwarfs, most notably Hans and Jacob Sass of Nebraska.

As hybridizing progressed, it became clear that complicated hybrids might not always fall into one of the intuitive categories being employed. In 1948, the AIS adopted a new set of classes defined by L. F. Randolph. Randolph rejected height as a decisive factor, and offered instead a rather vague notion that advanced generation hybrids that had "most of the characteristics of typical dwarf bearded irises" (he had in mind things like season of bloom, short foliage and stalk, lack of branching, etc.) would be considered DBs.

This way of thinking about the class was soon pushed to the breaking point. Hybridizers had begun importing and working with different species, outside the familiar I. lutescens and its hybrids. Robert Schreiner had imported seeds of the tiny cold-hardy species I. pumila from eastern Europe, and this exciting new species gradually spread among dwarf hybridizers. Paul Cook introduced the first hybrids between I. pumila and TBs in 1951: 'Baria', 'Fairy Flax', and 'Green Spot'. Although the term had not yet been invented, these were the prototype of what would become the modern classification of standard dwarfs. Did these new irises have "most of the characteristics" of dwarfs? At a mere 10 inches, they were less than 18 inches tall, to be sure, but did having a TB parent make them intermediates? They were sometimes branched, not a characteristic of "typical" DBs of the time.

DB 'Sapphire Night' (Nicholls, 1935),
perhaps a hybrid involving
 I. lutescens and I. aphylla,
12-14 inches in the author's garden.
Photo: Tom Waters

Cook registered his new hybrids as IBs, but to many iris fanciers that just seemed wrong. In 1954, AIS introduced a new height-based classification, where any bearded iris 15 inches tall or less was a DB, regardless of ancestry or other characteristics. This caused a schism with many dwarf enthusiasts.

Eventually the matter was settled by splitting the DB class in two: a miniature dwarf bearded (MDB) class with an upper height limit of 10 inches (reduced to 8 inches in 1976), and a standard dwarf bearded (SDB) class from 10 to 15 inches. The MDBs were the province of the Dwarf Iris Society, whereas the SDBs were regarded as medians and promoted by the Median Iris Society.

The effects of Cook's new hybrids were not limited to the classification system. Excited by the developments, dwarf hybridizers scrambled to use I. pumila and the new SDBs in their breeding. The 1950s was a transition decade: it began with nearly all DBs being cultivars or hybrids of I. lutescens, and ended with nearly all MDBs and SDBs being hybrids of I. pumila and TBs in varied proportions. The influx of TB genes brought plicatas, pinks, and ruffled blooms into the dwarf iris world; I. pumila brought dramatic and varied spot patterns.

What does this all mean for the collector of historic dwarf bearded irises? First, it is essential to understand that the DB class does not correspond to any single modern class. It spans the height range of both MDB and SDB classes, even extending into the IB class in some instances. In principle, every historic DB could be assigned to a modern class on the basis of height. However, height was not recorded in early registration data; so such determinations would require catalog descriptions or garden observations. The Median Iris Society attempted to make such reassignments for the IB, MTB, and BB classes, although I do not know of any similar undertaking having been made for the MDBs and SDBs.

Even if we were able to sort historic DBs into modern classes based on height, that would not capture the essential nature of the old category. It represents irises of different ancestry and genetic characteristics than the modern classes. The 8-inch height boundary is even less meaningful for the old DBs than it is for their modern successors. I. lutescens and its hybrids span this boundary, and there is seldom any meaningful difference between a 7-inch and a 10-inch DB.

I think the best advice for modern growers interested in collecting historic dwarfs is to approach them on their own terms: viewing the DB category in its own right with context that differs from modern hybrids. Starting from that perspective, one can then notice some similarities and comparisons that might be made: A DB that is a I. lutescens/pumila hybrid, for example, might resemble an MDB that is an SDB/I. pumila hybrid.

The historic DBs are harder to come by than modern cuiltivars, but it is worthwhile to acquire and grow a few. Not only will you be helping to preserve a window into iris history, you will also get to enjoy a type of iris that really has no modern counterpart.