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One of the first western American iris to be described was I. tenuis by Watson in 1881. This iris was originally placed in the series Californicae mostly, I believe, because of its geographical location. Later (in 1959), Lee Lenz placed it in the Section Lophiris with I. cristata. Despite its early discovery and description, it is one of the least well known probably because of its limited natural range. I. tenuis is known only from the upper parts of the Clackamas River drainage and parts of the nearby Molalla river drainage, al1 in Clackamas County in the tate of Oregon. This small Pacific Northwest endemic is abundant in its range often forming gigantic carpets covering several acres. It makes one wonder why it isn't more widely used in horticulture. It may be that such luminaries as Davidson and Mathew have stated that it grows in cool, shady and moist areas. However, in my personal experience, the best stands I have seen were among Rhododendron macrophyllum and small shrubs in recently logged areas. These areas of partial sun would be moist in winter but quite dry in summer. This may be the main reason that I. tenuis is not more widely known or established in gardens because of faulty context and exposure information! Another possible reason that I. tenuis is not well known is because it isn't easily transplanted and seems to be difficult to cultivate outside of its limited range. I have had two different clones of this iris in the past and could keep it no more than two or three years. I am quite sure that my own failures with I. Tenuis were due to giving it too much shade and moisture during the summer months. When I obtain I. tenuis again I will grow it in a little more sun.
The previously little known Korean Irises, l. odaesanensis and I. koreana, are now rapidly entering the trade. Both Garden Vision and Joe Pye Weed's Garden are offering I. odaesanensis this year. When 1 received one of these catalogues with a color picture of I. odaesanensis I kept returning to the picture, questioning in my mind why an iris I had never seen before even in a photograph should look so familiar. For two days I walked around with this in the back of my mind until one night it hit me- I. odaesanensis looks just like l. tenuis! Compare the two photos of I. tenuis and I. odaesanensis on page 3307. I know that looks alone mean little in deciding the relationship of species but this resemblance piqued my curiosity and I began to read what I could find on I. odaesanensis and the rest of the Chinenses series.
What I found is that several characteristics seem to be found consistently in most of the Chinenses series. In conversations with several growers I discovered that small nodules are found seasonally on the roots of several species in the Chinenses series. They have long been known to appear in fall on the roots of I. minutoaurea and this fact is mentioned in the British Iris Society's new book "A Guide to Species Irises". Recently AIS President Clarence Mahan stated he had also observed them on I. rossii. Darrell Probst also told me they were found on I. koreana and I. odaesanensis and that I should not worry that I had root nematodes! Their root nodules look very much like the nodules made by nematodes and closely resemble the storage nodules found on clover roots.
Though not mentioned in any reference literature that I have read, I have observed transverse veins like those found in the series Laevigatae in the leaves of I. koreana, I. minutoaurea, I. odaesanensis and I. speculatrix. I do not grow I. rossii or I. henryi so I cannot say if they are present in those latter species. I would appreciate any feedback or information from anyone who has these plants on whether or not these latter two species have transverse veins.
Another characteristic that is found in the Chinenses series is a low, undissected ridge on the center part of the signal area of the fall. This ridge ends in what might be described as a small pleat in the fall. It is very different from the crest found on members of the Lophiris section. There are other species of iris that have a similar ridge but not quite so distinct as those in the series Chinenses.
As mentioned at the top of this piece, Lee Lenz placed I. tenuis in the section Lophiris with I. cristata because of the ridge on the falls, a ridge that is identical to those in the
Chinenses series. This was the same morphological reason why I. speculatrix was also originally placed with I. cristata, in the section Lophiris, although now research by Professor Zhao has it aligned with the Chinenses series. We must question how much importance we place on this distinctive ridge on the falls of I. tenuis? Is it enough to align I. tenuis within the Chinenses series?
I must stress that I am not a taxonomist but merely a curious gardener and amateur botanist. However, after noting some of the similarities between I. tenuis and members of the Chinenses series, I immediately searched for someone in our area that was growing I. tenuis. I wanted to know if their I. tenuis also had transverse veins in the leaves and if anyone had noted nodules on its roots. Alas, after a couple of phone calls I realized that at this time of year I. tenuis is totally dormant. During dormancy the resting buds of I. tenuis look quite similar to the resting buds of I. cristata of the section Lophiris, the crested iris section to which I. tenuis is now assigned. The leaves of most of the species in the Chinenses series are at least semi-evergreen. So you see there is plenty of argument for I. tenuis to remain with the crested iris. (You can see why taxonomists are never out of work!)
A great deal more study must be done before we know how and if I. tenuis and the Korea species are related. Chromosome counts on all of them would be very helpful. I will keep you posted on my observations of I. tenuis and the irises in the Chinenses series as well as the small crested iris such as I. cristata and I. gracilipes. At present this article must end with that oft-heard phrase "To be continued".
Reference:
Roy Davidson "I. tenuis: Unique Oregon Endemic" Bulletin of the American
Iris Society Number 264, January 1987 Edited by The Species Group of the
British Iris Society, "A Guide to Species Irises Their Identification and
Cultivation" Cambridge University Press 1997
Edited by Bee Warburton, "The World of Irises", The American Iris Society
1978 (Assistant Editor Melba Hamblen)
Fritz Kohlein, "Iris", Timber Press 1987 (German edition 1981 )
James Waddick and Zhao Yu-tang, "Iris of China", Timber Press 1992
Brian Mathew, "The Iris", Timber Press 1981 reprint with revisions 1989
W. R. Dykes, "The Genus Iris", Dover Press republication 1974.
Reprinted by permission from the SIGNA Newsletter #64
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