Flora of North America species comparison

Species 2 (2 in the flora).

P. H. Raven (1969), like R. Raimann (1893) and others, placed together all species of Camissonia with a sterile apical projection on the ovary; however, it is clear from molecular evidence (R. A. Levin et al. 2004; W. L. Wagner et al. 2007) that the perennial species with this feature (Taraxia) are distinct from annual species (Tetrapteron) and do not share an immediate common ancestor with them. Tetrapteron has distinctive capsules that differ from those of other genera in its irregularly obovoid shape, woody walls, and especially the pointed wings on the distal half of each valve. In addition, species of Tetrapteron are acaulescent or nearly so and have anthers intermediate between the basifixed anthers of Taraxia and its close relatives, and the versatile anthers of other species in the former Camissonia. The two species of Tetrapteron often occur on clay soil and retain their seeds very late, long after the plant has otherwise died and shriveled, which probably accounts for their unique capsular attributes. Steve Boyd (unpubl.) has observed that T. graciliflorum has hygrochastic capsules and suspects that T. palmeri also does. Reproductive features include: self-compatible; flowers diurnal; autogamous and, sometimes, cleistogamous, or in T. graciliflorum rarely outcrossing and pollinated by small bees or flies (Raven). The unusual sterile projections on the ovary in Taraxia and in Tetrapteron are presumed to have arisen independently. The species of both are acaulescent, so that the projection on the ovary raises the flowers above the leaves and, presumably, makes them accessible to pollinators (R. A. Raguso et al. 2007).

(Discussion copyrighted by Flora of North America; reprinted with permission.)