Allozymic Differentiation Between Tolmiea menziesii and Tellima grandiflora (Saxifragaceae)

Tellima and Tolmiea are monotypic genera of Saxifrageae and part of a natural group that includes Conimitella, Heuchera, Mitella, and Tiarella. Natural intergeneric hybrids have been reported between several of these genera, including Conimitella and Mitella, Mitella and Tiarella, Tiarella and Heuchera, and Tellima and Tolmiea. Since members of this natural group are vegetatively very homogeneous and differ largely in floral morphology, the occurrence of hybrids between so many of these genera suggests that they may not be highly differentiated genetically. To test this hypothesis, Tellima grandiflora and Tolmiea menziesii were compared electrophoretically. Evidence from enzyme electrophoresis indicates a high degree of allozymic similarity between Tolmiea men- ziesii and Tellima grandiflora (I = 0.49). These two species are more highly differentiated than are species within genera of Saxifrageae, such as Heuchera and Sullivantia. However, the degree of allozymic differentiation between Tolmiea and Tellima appears comparable to that reported for congeneric species of other plant groups. Tolmiea and Tellima are monotypic genera of tribe Saxifrageae (Saxifragaceae). Tolmiea men- ziesii (Pursh) Torrey & A. Gray is a herbaceous perennial ranging from southern Alaska south- ward through British Columbia, Washington, and Oregon into northern California (Hitch- cock and Cronquist 1973). Previous studies (Soltis 1984a) have shown Tolmiea to comprise diploid and tetraploid cytotypes having 2n = 14 and 2n = 28, respectively. Diploid popula- tions occupy the southern portion of the species' range (fig. 1; see also fig. 1 of Soltis 1984b), whereas tetraploid populations are found in the northern portion of the range. The closely related Tellima grandiflora (Pursh) Dougl. has a very similar geographic distribu- tion, although it occurs over a slightly larger range. It occurs farther north and south than does Tolmiea, and is found east of the Cascades in northeastern Washington, northern Idaho, and southern British Columbia. We have made chromosome counts of populations from throughout the range of Tellima and all are dip- loid with 2n = 14.