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Distyly and Monomorphism in Villarsia (Menyanthaceae): Some Evolutionary Considerations
Annals of the Missouri Botanical Garden
Vol. 75, No. 3 (1988), pp. 761-767
Published by: Missouri Botanical Garden Press
Stable URL: http://www.jstor.org/stable/2399364
Page Count: 7
You can always find the topics here!Topics: Evolution, Alleles, Pollination, Plants, Breeding, Pollen, Seed production, Genera, Biological taxonomies, Anthers
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Distyly occurs in four of the five genera of the Menyanthaceae, as do breeding systems such as dioecy, gynodioecy, and homostyly that are believed to be derived from distyly. Most species of the largely Australian genus Villarsia are distylous, but the Western Australian V. albiflora has monomorphic (nonheterostylous) flowers and appears to be homostylous. Despite this, individuals of this species are self-incompatible, although most members of the four populations studied are intercompatible. The incompatibility system of V. albiflora appears to be controlled by multiple alleles. Another Western Australian species, V. parnassiifolia, has distylous flowers and strong self-incompatibility. Long x Long crosses of this species fail to produce seeds, but Short x Short crosses commonly produce a full complement of seeds. Thus, this species possesses a self-incompatibility system, but Shorts have an unexpectedly high degree of intramorph intercompatibility, suggesting that the incompatibility system of this morph likewise is controlled by multiple alleles. Five of eight natural populations sampled of V. parnassiifolia showed Short-dominated morph ratios, suggesting that offspring of Short x Short pollinations may constitute a portion of these Short-dominated natural populations. Villarsia albiflora may represent a recombinant homostyle, a true-breeding Short morph derived from a distylous ancestor with a breeding system similar to that of V. parnassiifolia, or a species possessing a floral morphology and breeding system ancestral to the distyly that occurs widely in the Menyanthaceae. A scheme for the origin of distyly in Villarsia is presented.
Annals of the Missouri Botanical Garden © 1988 Missouri Botanical Garden Press