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Self- and cross-pollinations were made within and between selected species belonging to Boykinia, Peltoboykinia, Bolandra, Suksdorfia, Sullivantia, and Jepsonia (Saxifragaceae). Self-incompatibility is reported for the first time in Boykinia. No intergeneric hybrids were produced, supporting the separate integrities of the genera involved, particularly the segregation of Peltoboykinia. Intrageneric hybrids were made in Boykinia and Peltoboykinia. In the case of Boykinia, this supports the retention within it of the often segregated Telesonix. Crosses between the two North American Suksdorfia species failed, but for various reasons, this was taken to reflect the existence of two "biological species" rather than two separate genera.

Chromosome numbers are reported for the first time for Boykinia intermedia (2n = 14), B. major (2n = 28), Peltoboykinia watanabei (2n = 22), and Suksdorfia (= Hemieva) ranunculifolia (2n = 14). Additional counts are provided for eight other species of Boykinia (including Telesonix), Peltoboykinia, Suksdorfia, and Bolandra. Previous literature reports are reviewed and some errors pointed out. Chromosome numbers do little to resolve the problem of generic limits, with the exception of supporting the segregation of Peltoboykinia. They do, however, support the recognition of Boykinia intermedia as a species distinct from B. major.

An evaluation of the limits and infra-generic taxonomy of the genus Boykinia and its allies is presented. In the past, Boykinia has been split into the following segregate genera: Boykinia and Telesonix (from North America) and Neoboykinia and Peltoboykinia (from Japan). The situation is complicated by other closely related genera, the limits of which also need clarification. Narrowly defined, they comprise Suksdorfia, Hemieva, Bolandra, Sullivantia and Jepsonia (all from North America) and Hieronymusia (from South America). This monograph draws on a variety of sources for information, including a morphological comparison of all taxa, using a wide range of both living and herbarium material, and observations on leaf anatomy, trichomes, pollen grains and seeds; reference is also made to our previously published work on flavonoids, chromosome numbers and breeding relationships. General ecological observations were made during field work in western North America. The results of these investigations confirm that the genera form a closely related group. Much of the evidence combines to suggest the following conclusions. Boykinia includes nine species in three sections: section Boykinia (B. aconitifolia, B. intermedia, B. lycoctonifolia, B. major, B. occidentalis and B. rotundifolia), section Renifolium (B. ruhardsonii) and section Telesonix (B. jamesii and B. heucheriformis). Peltoboykinia (P. tellimoides and P. watanabei) is recognized as a distinct genus allied to both Saxifraga and Boykinia. Suksdorfia, expanded to include Hemieva and Hieronymusia, has three species: S. violacea, S. alchemilloides and S. ranunculifolia. Bolandra is very closely related to Suksdorfia but is retained as a separate genus containing two species, B. californica and B, oregana. Sullivantia and Jepsonia are accepted as genera related to, but distinct from, Boykinia.