Sedum oblanceolatum

Abstract: Summary All 12 of the taxa in Sedum section Gormania are geographically restricted to western North America, occurring on a variety of rock outcrops that range in elevation from 55 to nearly 3700 meters. Evolutionary divergence of the taxa has been facilitated by temporal isolation of the flowering periods, cytological differentiation, and changes in the breeding systems. Species adaptation and restriction to particular substrates that are isolated in the geologically diverse Klamath region appear to have fostered narrow endemism of some of the taxa. Four of the taxa are putative relicts and are characterized as diploids, morphologically homogeneous, highly self-compatible, and narrowly restricted at low elevations to a single type of substrate. Vegetative reproduction in the relictual taxa is much less than that in related taxa. Those taxa that appear to be more recently evolved have at least two of the following features: tetraploidy or hexaploidy, morphological heterogeneity, extensive vegetative reproduction, low level of selfcompatibility, occurrence on geologically recent substrates, or a wide distribution. All of the taxa classified in Sedum section Gormania are endemic to exposed rock outcrops in western North America. Clausen (1975) included 11 taxa in section Gormania, but I have accepted only ten of these, and have described two additional ones endemic to the Trinity Mountains, making a total of 12 taxa recognized in the section (Denton, 1978). The center of distribution of section Gormania is in the floristically diverse Klamath region of northwestern California and southwestern Oregon, with some taxa extending southward in California in the North Coast Range and in the Sierra Nevada, and one taxon extending northward along the Oregon Cascades to Mt. Hood, Oregon. All occur between 37? and 46? North latitudes. My investigations of section Gormania have focused on the possible ways by which speciation has occurred and on the factors that may contribute to the limited distribution patterns. The geologic diversity of the Klamath region has been assumed to be a major factor in the adaptive radiation of various plant groups (Whittaker, 1960). This is substantiated to some extent in Sedum section Gormania as the taxa show varying degrees of specificity to particular rock substrates (Table 1). Six of the 12 taxa are known from only one type of outcrop. Although diorite, quartz diorite, and granodiorite are the most abundant types of rocks found in the Klamath area (McKee, 1972), peridotite and serpentine intrusions are extensive and produce noticeable effects on the vegetation. In the Gormania group, three of the taxa have been found only on peridotite (S. albomarginatum, S. laxum subsp. eastwoodiae, and S. moranii), while three others occur on peridotite and gabbro or basalt or rarely granite. Sedum oblanceolatum is known only on outcrops of diorite, S. laxum subsp. flavidum is found only on altered basalt, and S. obtusatum subsp. paradisum occurs only on granite. The four subspecies of S. laxum are centered in the Klamath Mountains and occur mostly on peridotite, and less frequently on basalt or gabbro. The four subspecies of S. obtusatum extend into the Klamath region, but are found principally in the Sierra Nevada and the North Coast Range on granite and granodiorite, and less commonly