Using Species in MDB Breeding, Part 3: Iris reichenbachii x Iris pumila

by Tom Waters

This is the conclusion of a three-part posting describing projects with miniature dwarf bearded (MDB) and standard dwarf bearded (SDB) irises. The first and second installments were posted in July and October 2023. 

My goal for this hybridizing project is to produce a true-breeding line of MDBs that belong to the same fertile family as the SDBs and MDBs from SDB breeding. In theory, using species and species hybrids that are compatible with SDBs will circumvent the tall bearded ancestry that can lead to larger, out-of-class plants. The earlier installments cover the use of Iris lutescens and of a hybrid of Iris aphylla x I. pumila. 

The current post describes work with seedlings from I. reichenbachii x I. pumila. This third avenue of work is, to me, the most exciting and promising. However, I got started with it a bit later than the first two approaches, so it is less far along.

I. reichenbachii is a species native to the Balkan peninsula. It comes in both diploid and tetraploid forms. (The tetraploid species I. balkana is considered a synonym of I. reichenbachii.) Plants typically have very slender stems topped with two buds, ranging in height from about 6 inches to about 12 inches. Flowers are either yellow in color or some blend of violet, brown, and gray. This species is probably best known as a parent of Paul Cook’s famous ‘Progenitor’ (R. 1951), which introduced the dominant bicolor pattern into tall bearded irises.

The tetraploid forms of the species belong to the same fertile family as TBs and I. aphylla. Hence crossing it with I. pumila ought to produce plants compatible with SDBs, just like the aphylla x pumila cross described in part 2.

tetraploid I. reichenbachii ex Mt. Vikos, Greece

I have raised a number of these (cross S026) from crossing a yellow tetraploid I. reichenbachii from Mt. Vikos, Greece, with I. pumila ‘Royal Wonder’ (Coleman, 2013). About half the seedlings are yellow and half are purple. They are all about 5 inches tall, with one or two dainty flowers per stalk. Because I. reichenbachii is so much smaller and daintier than I. aphylla, I believe these plants have even greater potential to produce consistently small and dainty MDBs. I have made as many crosses with them as possible. So far, they are not cooperating as pod parents, although they produce plenty of fertile pollen.

S026-02
I. reichenbachii X 'Royal Wonder'

 

S026-05
I. reichenbachii X 'Royal Wonder'

    

I am eagerly awaiting bloom in 2024 of seedlings from ‘Miniseries’ (Keppel, 2011) X S026-02. Still in the pipeline are crosses of the S026 seedlings with ‘Arson’ (Keppel, 2016, SDB), ‘Come and Get It’ (Black, 2013, SDB), ‘Dollop of Cream’ (Black, 2006), ‘Oh Grow Up’ (Miller, 2018), ‘Pearly Whites’ (Black, 2014), ‘Self Evident’ (Hager, 1997), ‘Tasty Treat’ (Johnson, 2020, SDB), and ‘Pirate’s Apprentice’ (Hager, 2003). 

Multi-generational breeding projects like this one require patience and a certain amount of faith in the theory behind them. It can be a long slog with little immediate gratification. But it can also be very satisfying to pursue curiosity about paths not taken before and to learn as one goes. For me, this type of undertaking matches well with my limited space and my penchant for careful planning. Perhaps in a few more years, the groundwork described in these three posts will yield something worthy of being grown in gardens or meriting the attention of other hybridizers. Until then, the learning itself is a fine reward.

The Untapped Potential of Iris reichenbachii

by Tom Waters

Today's post is all about an underappreciated bearded iris species, Iris reichenbachii. The name, it seems, is bigger than the iris itself. I. reichenbachii is a dwarf, ranging in height from 10 to 30 cm (4 to 12 inches), with one or sometimes two buds at the top of the stalk. (Very rarely, a third bud may appear further down the stalk.) The flowers are yellow (often with brownish markings or blending), smoky violet, or occasionally clear deep violet.

Iris reichenbachii

The species is native to the Balkan peninsula, from Rumania and Bulgaria through Serbia and into Greece. A related species, I. suaveolens, is similar but smaller. Two other species names, I. balkana and I. bosniaca, are now regarded as synonyms of I. reichenbachii.

As a garden subject, I. reichenbachii is pleasant enough, if somewhat unremarkable. It has found a home with rock gardeners and plant collectors. For those who fancy modern hybrid dwarf and median irises, this little species can seem drab by comparison. The petals are rather narrow, substance is lacking, and the colors can seem a bit murky.

To the hybridizer, however, I. reichenbachii has something unique to offer. Its chromosomes are very similar to those of tall bearded irises, and it is quite compatible with them. Furthermore, I. reichenbachii exists in both diploid (two sets of chromosomes) and tetraploid (four sets) forms. Since modern TBs and BBs are tetraploid, they can cross with tetraploid I. reichenbachii and produce fertile offspring. (For an explanation of diploids and tetraploids, see my earlier blog post Tetraploid Arils, Anyone?)

'Progenitor' (Cook, 1951)
 from I. reichenbachii X TB 'Shining Waters'

In the 1940s, the talented hybridizer Paul Cook did precisely that. A seedling from the cross, aptly named 'Progenitor', was registered in 1951. It was an unimpressive iris of intermediate size, but Cook could see its potential. 'Progenitor' was a bicolor, with violet falls and pure white standards. At the time, this was a new color pattern. (Earlier bicolors were actually variations on a "spot pattern" from I. variegata, and seldom showed the completely solid falls and pristine standards of 'Progenitor'. It is interesting to note that I. reichenbachii itself is not a bicolor. The bicolor pattern resulted from combining its genes with those of the TB parent. By crossing 'Progenitor' back to high-quality TBs, Cook was eventually able to transfer the bicolor pattern onto irises that otherwise showed no resemblance to the modest little dwarf that had given rise to the new pattern. 'Whole Cloth' (Cook, 1958), four generations on from 'Progenitor', won the Dykes Medal in 1962.

Virtually all TB and BB bicolors today (standards white, yellow, or pink; falls blue, violet, purple, reddish, or brown) are descendants of 'Progenitor', and hence of I. reichenbachii.

But there is still more to be done with this interesting little species. When Cook was making his crosses, there was very little interest in dwarf or median irises. In fact, medians as we know them today hardly existed at that time. So Cook simply worked to transfer the new color pattern into TBs. Today, however, there is considerable interest in breeding medians, especially BBs and MTBs that are consistently small and dainty. Surely the little dwarf I. reichenbachii has something to offer in these endeavors. The tetraploid forms are compatible with BBs and tetraploid MTBs, while the diploid I. reichenbachii could be crossed with diploid MTBs. Since these sorts of crosses should produce fertile seedlings, a hybridizer could continue the breeding line to achieve any desired goal.

Iris reichenbachii

I. reichenbachii is a little difficult to find in commerce, but not impossible. Some specialty nurseries list it, and if one is willing to grow from seed, it shows up rather often in seed exchanges that include iris species.

If you see this odd little species available somewhere, why not give it a try? Perhaps even make a cross or two to see what happens...