Those other Siberians

By Bob Hollingworth 

Did you know that there are two main groups of Siberian Irises? There are the beloved Siberians that most of us have in our gardens, which, in nature, have 28 chromosomes. These are the ones most people recognize as "Siberian irises".  But there is second group that has 40 chromosomes that is less well  known. These are sometimes called Sino-siberians since they come from the mountains of southwest China and adjacent areas over into the Himalayas.

I. forrestii

  Since the chromosome numbers don't match well, hybrids between the two groups (subseries) are uncommon, though a few are known. The most familiar is probably 'Foretell' (McGarvey 1970). I'm not aware of any other that has been registered since then, so this inter-subseries cross has not been a very fertile area for hybridizers (although speaking of fertility, surprisingly, 'Foretell' is modestly fertile with the 28 chromosome group).

I. chrysographes (black form)

     The 40 chromosome group have some affinity with the Pacific Coast irises which also have 40 chromosomes, and a number of crosses between these (Cal-sibes) have been produced. So far they are sterile unless they are converted to tetraploids.

'Dotted Line' (Reid 1992)

'Bronzy Marvel' (Reid, 1998)

     The number of species in this 40 chromosome group is a bit uncertain but probably runs from 6 to 8, so there is a lot of genetic variability available for hybridizers, and, unlike the 28 chromosome group, there are two natural yellow flowered species - I. forrestii and I. wilsonii. Another member of the group, I chrysographes, may be familiar to many since it has forms that are as near black as irises get.  

Spence seedling 0840-030A

Spence seedling 0640-011E

Spence seedling 0840-024A

     Over time this group has attracted several hybridizers and a variety of beautiful cultivars have been produced. Probably foremost in this regard is Lorena Reid in Oregon with such lovely creations as 'Dotted Line' (1992) and 'Bronzy Marvel' (1998). Others breeders outside the US  include Tomas Tamberg (Germany) and Jennifer Hewitt (UK). However, more recently, the area has fallen on hard times in the US, primarily due to massive losses in hybridizers' gardens from the build up of fungal (phytophthora) problems, and until recently there seemed to be little activity left.
     So, it is good to see the area coming back to life. In particular Patrick Spence is producing new 40 chromosome hybrids at Cascadia Gardens in Washington state. If interested, you might like to check out an article on the 40s by Patrick in the most recent (Fall 2012) The Siberian Iris. Some of his recent seedlings are shown here too.

 'Blue Meadow Fly' (Ahlburg, 1986)

     All the discussion so far has focused on growers in the Pacific Northwest where the climate particularly favors "the 40s". They need a fertile, somewhat acidic soil, year round moisture, some winter cold, and generally a moderate climate. Does this mean they cannot be grown elsewhere in the US? Probably not. Years ago, Currier McEwen grew and hybridized them in Maine as did Bill McGarvey in New York state. We recently acquired one ('Blue Meadow Fly', M. Ahlburg, 1986), found by chance growing at a nursery in Wisconsin, and it has flowered well here in Michigan for the last two years.
     So, if you can provide the requisite conditions and want to try something different, maybe give the 40 chromosome Siberians a try. And, if you like to take the road less traveled as a hybridizer, this is an area of opportunity. My guess is that the genetic potential here has only just started to be tapped.
(Thanks to Margaret Spence for several of the photos used here.)