Enantiostyly in Wachendorfia (Haemodoraceae): the influence of reproductive systems on the maintenance of the polymorphism.

Enantiostyly is a form of directional asymmetry in plants in which the style is deflected away from the main axis of the flower, either to the left or right side. In Wachendorfia (Haemodoraceae), a small genus of insect-pollinated geophytes restricted to the Cape Province of South Africa, populations are usually polymorphic for asymmetry. Here we investigate dimorphic enantiostyly in the four species of Wachendorfia to determine whether variation in their reproductive systems influences the maintenance of this genetic polymorphism. Experimental field pollinations of W. paniculata and W. thyrsiflora indicated higher fertility for cross- than for self-pollinations, whereas in W. brachyandra, these types of pollination produced similar levels of fertility. Outcrossing rates were highest in W. paniculata (t = 0.78-0.98), with W. brachyandra (t = 0.39-0.79) and W. thyrsiflora (t = 0.76) exhibiting mixed mating systems. Outcrossing rates in two populations of W. parviflora varied from mixed mating (t = 0.61) to predominant selfing (t = 0.07). Population style-morph ratios ranged from 1 : 1 in outcrossing W. paniculata to monomorphism in selfing W. parviflora and clonal W. thyrsiflora. In W. brachyandra, a species with delayed selfing, morph ratios were usually biased. The maintenance of enantiostyly in Wachendorfia appears to be strongly influenced by levels of disassortative mating and the balance between sexual and clonal recruitment.