Flowers are yellow-green, 2.5 mm in diameter, pedicels are nonparticulate; perianth is 2 mm long; 8 nectaries are yellow, alternating with stamens, being homostyly
, that is, self-pollinated flowers; stigmas are capitate.
It is believed that homostyly in this genus was derived from the breakdown of heterostyly as a general trend in evolution (Yasui et al., 1998).
The relationship between the self-compatibility and self-incompatibility alleles is described as S > [S.sup.h] > s with S the self-incompatible (thrum) allele dominant to both [S.sup.h] for self-compatible (homostyly) and to s, the self-incompatible (pin) allele.
and fecundity in Amsinckia spectabilis (Boraginaceae).
The simplest assumption about distyly is to treat it as an unordered character with transitions in either direction between distyly and homostyly
being equally likely (equal weighting).
This floral condition is referred to as homostyly
following Darwin (1877) and other workers on heterostylous groups (e.g., Ornduff 1972; Ganders 1979), who have assumed that homostylous species are derived from heterostylous ancestors through loss of floral morphs and selection for self-fertilization.
Using morphological and karyological information, Ray and Chisaki (1957b) proposed four separate evolutionary transitions from large-flowered heterostyly to smaller-flowered homostyly
. Their hypothesis is consistent with restriction-site variation in the chloroplast genome (Schoen et al., unpubl.).
The genetics of distyly and homostyly
in Turnera ulmifolia L.