A population study of three iris (iridaceae) species native to the Siskiyou Mountains in southwestern Oregon and adjacent California

Abstract

The series Californicaeis a natural grouping of Iris species native to Oregon, Washington and California. Natural and experimental hybridization is characteristic of the series which has led to confusing taxonomies for some species. Populations of species belonging to this series and found on the northwestern slopes of the Siskiyou Mountains cf southwestern Oregon and adjacent California were investigated. Methods used 2 were numerical classification techniques for morphological characters including both discriminant and K-means cluster analyses and a chemotaxonomi c analysis of flavonoid pigments using thin layer chromatography.The thirteen populations were found to represent three species: Iris doug'lasiana, Irais innominata, and Ir>is thompsonii. This study does not support the current taxonomy for I. thompsonii .which places it under I. innominata as a color form or in some populations as a hybrid between the species and I. dougZasiana. Differences were found in the intraspecific variation of the three species. I. innominata was a homeogeneous species and I. thompsonii was quite variable over its range. These differences may well reflect the unique character of this area. Although hybridization is possible between sympatric populations over the entire study area, mechanisms such as habitat preference and blooming time may well reduce gene flow. Two populations were found which may represent current hybridizations.