Species of Didymaea are characterized by their procumbent or climbing stems, opposite leaves with ovate, oblong-ovate, lanceolate, elliptic, or rarely linear blades, small, shallowly to deeply bilobed or geminate interpetiolar stipules, axillary inflorescences with small, bisexual homostylous
flowers with calyces reduced or absent, small, white to purple corollas with short tubes and 4-valvate lobes, 4 stamens with dorsifixed anthers, 2-locular ovaries with one axillary ovule per locule, and black, drupaceous fruits that are dimidiate and deeply bisulcate or sometimes subglobose.
form of buckwheat with short floral organs.
Our studies (Li & Johnston, unpubl.) on the development of various floral morphs in Amsinckia spectabilis (Boraginaceae) also indicate that both paedomorphic and peramorphic ontogenies are involved in the derivation of small homostylous
flowers from their putative ancestor; namely, populations having large distylous flowers (see section IX.B).
The genus Houstonia includes an array of homostylous
, distylous, short-styled (presumably self-compatible) and even cleistogamous species (Lewis, 1962), so it seemed important to test for heteromorphic self-incompatibility in our species.
1989) and the geographical distribution of heterostylous and homostylous
forms in Amsinckia spectabilis (Ganders 1975).
Waltheria carmensarae, a homostylous
species from northeastern Argentina, southeastern Paraguay, and central Venezuela, and W.
The main difference between the species is that the former is heterostylous and the latter homostylous
Less is known about the mating system of the homostylous
species, though these taxa often have flowers of reduced size, and they generally self-pollinate spontaneously.
Quantitative genetics of floral characters of homostylous
Turnera ulmifolia var.
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.
Other populations are homostylous
, the anthers and stigma occurring at nearly equal heights.
Quantitative genetics of floral characters in homostylous
Turnera ulmifolia var.