Genetic diversity in three colonizing orchids with contrasting mating systems.

Comparative studies on the genetic attributes of colonizing orchids with diverse mating systems are lacking in the literature. Eulophia sinensis, Spiranthes hongkongensis, and Zeuxine strateumatica are colonizing orchids that frequently occupy newly created habitats in Hong Kong. Mating system studies showed that E. sinensis is a self-compatible but pollinator-dependent outcrossing species, S. hongkongensis is a self-pollinating taxon, and Z srateumatica is apomictic. Population genetic attributes of these orchid species were investigated. Despite their contrasting mating systems, electrophoretic surveys revealed a striking lack of allozyme variation, both within and among populations, in all three species. However, gene duplications were evident in these species, due to their likely polyploid origins, The percentage of duplicate loci exhibiting "fixed heterozygosity" was 10, 21.4, and 20% in E. sinensis, S. hongkongensis, and Z. strateumatica, respectively. The genetic attributes of these orchids are compared to those found in other colonizing plant species.