Cytogenetic and Pollination Studies in the Genus Verticordia DC

Abstract

Aspects of the genetic and physiological barriers to hybridisation have been assessed for the genus Verticordia which contains many species with significant potential for ornamental horticulture. The chromosome numbers of 52 species were analysed using flower buds and root tips. Previously published reports on chromosome numbers were confirmed for 21 species and new numbers reported in a further 31. Self compatibility was present in 20 species and only three species were shown to possess barriers to self pollination. Seed set occurred in two of six interspecific crosses carried out within sections. In 21 wider crosses the degree of pollen tube development was increasingly repressed with taxonomic distance.

The chromosome counts also support the reclassification of the genus Verticordia into three subgenera: Chrysoma, Verticordia and Eperephes. Species within each section of a subgenus generally had the same chromosome number. Exceptions occurred in the subgenus Verticordia, sections Verticordia, Intricata and Micrantha.

In species with one or two ovules, the chromosome number was also low (6, 7, 8 or 9) while species with six or more ovules had a higher chromosome number (11 or 22). There was, however, no relationship between chromosome number and chromosome size, nor between chromosome number and any observed feature which might be attributable to polyploidy or allopolyploidy. With the possible exception of V. grandis, which displayed loss of seasonality in flowering, all putative polyploids behaved developmentally as diploids and displayed a high level of male fertility.