Growth forms and sepal hairs of the purple saxifrage (Saxifraga oppositifolia: Saxifragaceae) in North America related to chromosome records and DNA information

Abstract

Growth forms and the presence or absence of hairs on the surfaces of the sepals of Saxifraga oppositifolia L. plants were examined on type specimens and more than 400 herbarium specimens collected from all over North America and Europe. Data were gathered on whether plant growth forms were compact, trailing, or intermediate between the extremes. Specimens were examined for whether or not hairs were present on the surface of the sepals between the long trichomes on the margins, and if so, an estimate was made of the degree of hairiness. While extreme forms of compact and trailing plants do occur, maps indicate that more of the plants collected in North America were intermediate in growth form. The geographic distribution of the presence or absence of hairs on the sepals is mapped, as is the gradation in degree of hairiness of sepals. The type specimen of S. oppositifolia subsp. smalliana (S. pulvinata), from the Yukon, has compact plants and flowers that have sepal surfaces with a few sparse hairs. The flowers have set fruits that have opened. “The smaller turbinate hypanthium” described in the original description may be the result of the structures being dehisced and dried up fruits. The type specimen of S. oppositifolia subsp. glandulisepala , from Alaska, is a relatively trailing specimen with some larger leaves. The sepal surfaces have a few glandular hairs. Whether or not the hairs appear glandular on herbarium specimens may reflect the stage of flowering at the time of collection. No morphological differences are associated with three different chromosome numbers known for S. oppositifolia plants from the area of the North American type specimens, and DNA analyses done mainly on European specimens, but also including a potential candidate for the name “smalliana”, gave inconclusive results. Thus, chromosome and DNA data join these morphological data on growth forms and the occurrence of sepal hairs to discourage recognizing subspecies among plants occurring in North America.