805 
The breeding system of Villarsia exaltata 
(Menyanthaceae), a distylous species 
Robert Ornduff 
Abstract 
Ornduff Robert, Department of Integrative Biology, University of California, Berkeley, California 
94720-3140 USA) 1996. The breeding system o/Villarsia exaltata (Menyanthaceae), a distylous species. 
Telopea 6(4): 805-SII. Ten of the 15 species of the predominantly Australian genus Villarsia have 
distylous flowers. Eight of these are diploid or predominantly so. In six species the incompatibility 
relationships within and between the two morphs resemble the expect^ type^ but the distylous 
breeding systems of four species deviate from that conventionally associated with distyly. This 
paper reports on the breeding system of the widespread eastern Australian Villarsia exaltata, which 
has distylous flowers, striking dim.orphisms in style length and stigma morphology of the bvo 
floral types, high pollen stainability, but not consistent intermorph size differences in the pollen 
grains. Unlike the other distylous Australian species, V. exaltata is hexaploid. Intermorph pollinations 
of pin plants (those with long-styled flowers) produced 5.6 times more seeds than intramorph 
pollinations; intermorph pollinations of thrum plants (those with short-styled flowers) produced 
33.4 times more seeds than intramorph pollinations. Thus an incompatibility system is associated 
with distyly in this species; the system appears to be stronger in thrum plants than in pin plants. 
Pollinations utilizing different pairs of parent plants often differed in mean seed-sets following a 
given class of pollination. Some intramorph pollinations produced unexpectedly high seed-sets 
that were equal or nearly equal to those produced by intermorph pollinations of the same seed 
parent. The breeding system of V. exaltata is not considered to represent a condition ancestral to 
the derivative breeding systems associated with distyly elsewhere in the genus, but it demonstrates 
the kind of intrapopulation variability that is necessary before natural selection can lead to the 
development of these derivative systems. Little is known of the population biology or the 
functioning of distyly in natural populations of V. exaltata, features that would reward study by 
botanists resident within the range of this species. 
Introduction 
Distyly is a genetic polymorphism conventionally defined by reciprocity in positions of 
stigmas and anthers of the flowers of the two morphs (Barrett 1992). Long-styled 
flowers are termed pin flowers, and short-styled flowers are termed thrum flowers 
(Darwin 1877). Distyly has been reported in over two dozen angiosperm families (Lloyd 
and Webb 1992). Commonly it is associated with strong intramorph incompatibility 
and strong intermorph compatibility and by differences in size and other features of 
pollen grains and stigmas of the two morphs. There are other less widespread features 
associated with distyly in various species (Lloyd and Webb 1992). Ten of the 15 species 
of the predominantly Australian genus Villarsia (Menyanthaceae) are distylous (eight 
of these are diploid or predominently so) and four species are not heterostylous (Ornduff 
1982, 1986, 1988a, b, 1992); the floral condition of V. cambodiana Hance is unknown 
(Ornduff 1994). Four Western Australian species of Villarsia exhibit more or less 
conventional distyly, with the expected intramorph incompatibility and intermorph 
compatibility, pollen size differences, and reciprocal positions of anthers and stigmas 
(Ornduff 1982,1988a,b, 1992, unpublished; see following discussion). In two distylous 
Western Australian species both morphs are self-incompatible, pin plants are cross¬ 
incompatible, and thrum plants show high levels of cross-compatibility (Ornduff 1988b, 
in press; see following discussion). In two other distylous Western Australian species 
