Iris growers are certainly familiar with Siberian iris.This group is perhaps the most important among the beardless irises. Certainly, they have been hybridized for many years such that today, there are hundreds of hybrids available in a rainbow of colours. However, the purpose of this article is to go back to the roots (no pun intended) of the Siberians to discuss the species.
There are surprisingly few species within the Siberian group, and in themselves, they fall into two distinct group; the 28-chromosome group and the 40-chromosome group. The former are considered the standard Siberians while the second group are often called the Sino-Siberians. Despite both groups being lumped into the Siberian iris, you cannot create hybrids between the two groups as their chromosome numbers make them incompatible.
Most of the classic Siberian iris hybrids are from the 28-chromosome group and are derived from I. siberica and I. sanguinea. Iris siberica, despite the name, hail primarily from central and eastern Europe, but do extend into Turkey and western Russia. The distribution of I. sanguinea is further east than I. siberica, from southeast Russia to Korea and Japan. While similar in appearance with classical blue flowers, wild forms are relatively easy to separate. The flower stems of I. sanguinea are shorter than their leaves, are unbranched with 2 flowers/stem and are larger in size. Iris siberica has branched flower stems that are taller than the leaves. Wild I. sanguinea also blooms a week earlier than wild I. siberica. The wild forms are not particularly common in cultivation although they have a certain grace. 'Flights of Butterflies' comes close in appearance to wild I. siberica while 'Snow Queen' is a white-flowered selection of I. sanguinea (although often sold as I. siberica). A third species called I. typhifolia, is rare in cultivation and has been little used in today's modern Siberian hybrids. It is perhaps the most elegant of the 28-chromosome Siberians with blue flowers that appear similar in shape to Spuria iris.
Iris siberica and the alba form
Wild form of I. sanguinea and I. sanguinea 'Snow Queen'
The Sino-siberian iris are composed of 7 species. Two are yellow-flowered and these include I. forrestii and I. wilsonii, both from western China. These two appear quite similar but the standards of I. forrestii are stiffly upright while those of I. wilsonii are held at a 45 degree angle. The flower stems of I. wilsonii are about the same length as the leaves while I. forrestii has stalks taller than their leaves. Between the two species, I. forrestii blooms about 2 weeks earlier than I. wilsonii. Generally, I. forrestii is of smaller stature than I. wilsonii.
Iris wilsonii vs. I. forrestii
Iris chrysographes is perhaps the most popular of the Sino-siberians. In the wild, they hail from SW China. This iris is most famous for its ‘black' forms which indeed, appear black, although upon close inspection, they are deep reddish-violet. The wild forms are varying shades of reddish-violet with at least a few gold flecks at the base of the falls.
Examples of I. chrysographes
Iris delavayi, from southwestern China, is similar to I. chrysographes but is rich purple-blue with more diffuse cream spotting at the base of the falls. This is the tallest of the sino-siberians reaching 3 to 4 feet, but possibly up to 5 feet. Their leaves are distinctively shorter than the flower stalks. The standards are held upright. Iris clarkei occurs in western China and neighboring Nepal, Tibet and India. It is the only species in the group with solid flower stems (the rest have hollow stems). It is also quite distinct in having branched flower stems. The standards are held at a low angle (almost horizontal) and the falls have a large, distinct pale yellow eye at their base surrounded by a dark blue band, which strongly contrasts with the medium blue flowers. This eye pattern is often passed along to its hybrids.
Iris delavayi and I. clarkei
Iris dykesii is a rather obscure Chinese species hardly known in cultivation and may in fact, be a natural hybrid. Finally there is I. bulleyana. For years, it was thought to be a hybrid between I. chrysographes and one of the yellow-flowered species, however, deliberate crosses between these species have never developed into a plant that looks like the wild I. bulleyana. I was fortunate to obtain seeds which were wild-collected in Yunnan, China. The resulting plants have been of shorter stature than any other sino-siberian species, with stems reaching 20 inches. The blooms are medium violet-blue with falls distinctively streaked with cream.
Iris bulleyana grown from wild-collected seed in Yunnan
All of the sino-siberians require evenly moist soil and prefer humid climates that are not too hot. A soil that is slightly acidic is better than those which are alkaline. They are rather poor performers in the midwest where the standard siberians do much better. I should also note that the siberians are not as prone to insects and diseases as the bearded iris. If you are fortunate to live in a climate where they do well, it is hard to beat this group of iris species for their exquisite and graceful blooms.