MILLER, JILL S. University of Colorado, Department of Environmental, Population, & Organismic Biology, Campus Box #334, Boulder, CO 80309. - Floral morphometrics and the evolution of sexual dimorphism in Lycium (Solanaceae).
Gender dimorphism has evolved at least twice in the genus
Lycium (Solanaceae) and occurs in three species that are
present in southwestern North America. Plants of L.
californicum, L. exsertum, and L. fremontii are
either male-sterile (i.e., female) or perfect-flowered (i.e.,
hermaphroditic) and populations are morphologically gynodioecious.
Eleven floral characters were measured on female and hermaphroditic
plants for the three North American dimorphic species to characterize
sexual dimorphism between flowers on female and hermaphroditic plants.
Despite notable shifts in floral size and shape among the dimorphic
species, the general pattern of floral dimorphism between females and
hermaphrodites was similar for all three species and consistent with
the single origin of gender dimorphism in North America. Specifically,
flowers on female plants are smaller than on conspecific
hermaphrodites and have a long style equal to or slightly exerted from
the corolla tube and reduced stamens with abortive anthers. Flowers on
hermaphrodites are more flaring than on females, have a style of
variable length and long stamens with fertile anthers that are
typically exerted from the mouth of the corolla tube. However, the
degree of sexual dimorphism between females and hermaphrodites varied
among the dimorphic species, suggesting that flowers on females and
hermaphrodites of the three species may be specialized for gender
function to different degrees. In addition, morphometric measurements
for the dimorphic species were compared to five species of cosexual
(i.e., hermaphroditic) Lycium. These data, along with the
presence of a phylogenetic hypothesis, allowed historical
reconstruction of the shifts in floral size and shape across the
transition from cosexuality to gender dimorphism.
Key words: floral morphology, gynodioecy, Lycium, sexual dimorphism, Solanaceae