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Generic limits and systematics of boykinia and allies (Saxiferagaceae) Gornall, R. J.

Abstract

The goals of the study were to define the limits of the genus "Boykinia" and to clarify its infrageneric taxonomy. As circumscribed by Engler, "Boykinia" contained nine species in three sections. Three segregate genera have been described however, and at its most fragmented, Engler's "Boykinia" would comprise: "Boykinia", "Neoboykinia", "Peltoboykinia" and "Telesonix". The situation is complicated by other closely related genera, whose limits also need clarification. Narrowly defined, they include "Suksdorfia", "Hemieva", "Hieronymusia", "Bolandra" and "Sullivantia". Methods of approach included an examination of a wide range of herbarium material to allow morphological comparisons of all taxa. Live plants of almost all species were maintained in cultivation and some anatomical observations were made, and an intra- and inter-generic hybridization programme was conducted, on these. The trichome complements of each genus were investigated. Pollen grains and seeds were examined by light and scanning electron microscopy. Chromosome numbers were confirmed or established for the first time for all but three species. A complete flavonoid analysis of representatives of all genera, including all species of "Boykinia" s.1., was conducted. General ecological observations were made during field work in Alaska and the Western Cordillera of Canada and the U.S.A. The results of these investigations confirmed that the genera form a closely related group. However, much of the evidence combined to suggest the following conclusions: 1) "Boykinia" comprises nine species in three sections (section "Boykinia" includes "B. aconitifolia", "B. intermedia", "B. lycoctoriifolia", "B. occidentalis", "B. rotundifolia" and "B. major; section Renifolium includes "B. richardsonii; and a new section, Telesonix, includes "B. jamesii" and "B. heucheriformis. 2) "Peltoboykinia tellimoides" is recognised as a distinct monotypic genus, with as much affinity with "Saxifraga" as with "Boykinia". It has two subspecies: ssp. "tellimoides" and ssp. "watanabei". 3) "Suksdorfia" is expanded to include "Hemieva" and "Hieronymusia", making a total of three species: "S. ranunculifolia", "S. violacea" and "S. alchemilloides". The range of variation in "Suksdorfia" is similar to that in "Boykinia" and the two genera are considered to have evolved in parallel. 4) "Bolandra" is provisionally retained as a separate genus. It is very close to "Suksdorfia", and further work on "B. californica", which is closest in terms of gross morphology, may lead to a merging of these genera. 5) "Sullivantia" is a distinct genus. Geographical distributions, together with the taxonomic data, allowed some speculation on the evolutionary relationships of the genera. "Boykinia" is probably a Tertiary relict, since it has a disjunct distribution between Japan, western North America and eastern North America. It may share a common ancestor (a "Saxifraga"-like plant) with "Peltoboykinia", which is endemic to Japan. The remaining genera have probably evolved from "Boykinia" stock by adaptive radiation into different habitats. "Sullivantia", an inhabitant of wet cliff faces, probably diverged first. "Suksdorfia" and "Bolandra", characteristic of open and shaded, spring-wet, summer-dry habitats respectively, probably evolved later, in response to the onset of such a climate in the late Pliocene.

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