Chromosome Numbers and Relationships in Tribe Hemimerideae (Scrophulariaceae)

Abstract

Chromosome numbers are presented for five genera in the Hemimerideae. Mitotic counts were made for 69 species of Diascia, seven species of Nemesia, six species of Alonsoa, four species of Hemimeris, and two species of Diclis. At the species level, 80 of these counts are new reports. Counts for two genera (Diclis and Hemimeris) are also new. Diascia has a base number of x = 9 and most species are diploid. Four tetraploid and one hexaploid species were discovered among the perennials of section Racemosae, bringing the total number of polyploids for the section to seven of 26 species (ca. 27%). Two species in section Racemosae have more than one cytotype; D. patens has 2n and 4n populations, whereas D. capsularis has 2n, 4n and 6n populations. In section Diascia, consisting entirely of annuals, only five of 46 species (ca. 11%) are tetraploid, while the rest are diploid. Polyploidy has apparently had multiple origins in both sections of Diascia. The seven species of Nemesia counted were uniformly 2n = 18, but hypotheses of a close relationship between Nemesia and Diascia conflict with differences in corolla aestivation and preliminary molecular evidence. Hemimeris and Diclis are diploid with 2n = 14 and appear to be closely related. Alonsoa is also related to Hemimeris with South African species having 2n = 28 and South American species mostly 2n = 56. Chromosomal, pollination and morphological differences between South African and South American species suggest that Alonsoa originated in South Africa and dispersed to South America before or shortly after the breakup of Gondwanaland. If true, the Scrophulariaceae has had a more ancient presence in the Southern Hemisphere than previously suspected.