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.

Iris lutescens: The Dwarfs that Time Forgot

by Tom Waters

Dwarf bearded irises may be found growing wild throughout much of southwestern Europe, from Spain and Portugal, through southern France, and into northern and central Italy. Through the centuries, different botanists have encountered them in different localities and assigned different names to them: Iris chamaeiris, I. italica, I. olbiensis, I. lutescens, I. virescens, I. subbiflora, I. bicapitata.

Iris lutescens, raised from seed

By the twentieth century, it was clear that most, if not all, of these were really irises of the same species. Gardeners were most familiar with those from southern France, going by the name of I. chamaeiris, so began referring to the whole species as the “chamaeiris complex”. But the rules of botanical nomenclature require that synonyms be resolved by using the earliest published name for the species. In this case, that honor goes to I. lutescens, the name used by Lamarck in 1789. This is now the correct name for all these irises, with the exception of two irises at the extremities of the species’ range,  I. subbiflora in Portugal and I. bicapitata in the Gargano peninsula of eastern Italy, which are regarded by many (though not all) botanists as distinct species in their own right. Even if these are not regarded as belonging to I. lutescens, they are indisputably very close relatives.

I. lutescens is a delightfully varied species. The flowers are most often yellow, cream, or violet, but there are near-white forms, purples, blends, and bitones. In height, they range from about 6 to 12 inches (15 to 30 cm). The stem is unbranched, with one or two terminal flowers.

Iris lutescens 'Bride' (Caparne, 1901)

Until the second half of the twentieth century, I. lutescens  and a handful of its accidental hybrids with other species were the only dwarf bearded irises known to gardeners in western Europe and North America. Named cultivars were produced by the firm of Goos and Koenemann in Germany, by W. J. Caparne in England, and later by Hans and Jacob Sass, among others, in the US. At this time, the modern dwarf and median classes did not exist, so there was no distinction between miniature dwarfs and standard dwarfs; they were all simply “dwarf bearded”, and spanned the whole natural height range of the species, which straddles both of the modern categories.

Iris lutescens 'Path of Gold' (Hodson, 1941)

Although many people grew a few dwarfs, appreciating their charm and early bloom, almost all the attention of iris enthusiasts in the first half of the twentieth century was focused on the tall bearded. The dwarfs were rather taken for granted, by both gardeners and hybridizers. That began to change with the formation of the Dwarf Iris Society under the leadership of Walter Welch in the 1940s. Welch and his friends were determined to learn all they could to advance dwarf hybridizing, and their interest went beyond the I. lutescens cultivars to investigate other dwarf species, such as I. pumila from eastern Europe.

I. pumila is a diminutive species, about half the height of I. lutescens, single-flowered and almost stemless. Robert Schreiner had imported some seeds in the 1930s, and the species gradually became available to the new dwarf hybridizing enthusiasts. The turning point came in 1951, when Paul Cook in Indiana, who had exchanged his pumila pollen for TB pollen from his friend Geddes Douglas in Tennessee, introduced the first pumila/TB hybrids: ‘Baria’, ‘Green Spot’, and ‘Fairy Flax’. Although technically “intermediates” (as the word was used then, it meant a hybrid between dwarf and tall bearded irises), these new irises were no larger than many I. lutescens dwarfs, even though they often had a branch and a total of three buds! This launched a vigorous debate about classification, which led ultimately to the formation of the Median Iris Society and the four median classes we have today. The SDB class was created to accommodate the new pumila/TB hybrids and the taller I. lutescens cultivars, with the MDB class left for the “true dwarfs”, with a maximum height limit of 10 inches, later adjusted to 8 inches.

From the 1960s on, the SDBs from pumila/TB breeding totally dominated the world of dwarf irises. These SDBs carry an extraordinary genetic legacy (dramatic spot patterns from I. pumila, pinks and plicatas from TBs, not to mention more modern form). There was no interest any more in producing more of the overly familiar yellow or violet I. lutescens cultivars. Even the MDB class was taken over by the new SDBs. Most MDBs from the 1960s onward were produced by crossing the new SDBs back to I. pumila, or (especially in recent decades), just selecting irises from SDB breeding that happen to be under the height limit.

I. lutescens, once the very archetype of the dwarf bearded irises in gardens, is now a curiosity known only to species enthusiasts.

Is there any hope for a lutescens renaissance? At first blush, it would seem unlikely. The modern SDBs have been so developed by decades of dedicated hybridizing that they would seem to have nothing to gain (and much to lose, in terms of present-day expectations of the class) by the injection of I. lutescens into hybridizing lines.

If I. lutescens is to be heard from again in dwarf hybridizing, the opportunity may be in the MDB class. Some MDB enthusiasts have been grumbling of late that the class has been taken over by short SDBs, and is losing something of its distinctive charm. There may be some niche here for MDBs with more of a “wildflower” look, breaking away from the stiffness, width, and ruffling that comes from pure SDB breeding. Just as the MTB class has given a home to the simpler, more modest look of the diploids, perhaps there is an opening for more “retro” MDBs. I. lutescens is fully fertile with SDBs and their MDB progeny, and might add a breath of fresh air to a class that is starting to feel overworked.

Everything old is new again?

Iris lutescens campbelli

The World of Irises is the official blog of The American Iris Society. Now in its 99^th year, The American Iris Society exists to promote all types of irises. If you wish to comment on a post, you can do so at the end of the page and the author or the editors will reply. If you wish to learn more about The American Iris Society, follow the link.