Flower morphology, pollination biology and mating system of the complex flower of Vigna caracalla (Fabaceae: Papilionoideae).
OBJECTIVE
Vigna caracalla has the most complex flower among asymmetrical Papilionoideae. The objective of this study was to understand the relationships among floral characteristics, specialization, mating system and the role of floral visitors under different ecological contexts.


METHODS
Five populations were studied in north-western Argentina, from 700 to 1570 m a.s.l. Anthesis, colour and odour patterns, stigmatic receptivity, visitors and pollination mechanism were examined and mating-system experiments were performed.


RESULTS
The petals are highly modified and the keel shows 3.75-5.25 revolutions. The sense of asymmetry was always left-handed. Hand-crosses showed that V. caracalla is self-compatible, but depends on pollinators to set seeds. Hand-crossed fruits were more successful than hand-selfed ones, with the exception of the site at the highest elevation. Bombus morio (queens and workers), Centris bicolor, Eufriesea mariana and Xylocopa eximia trigger the pollination mechanism (a 'brush type'). The greatest level of self-compatibility and autonomous self-pollination were found at the highest elevation, together with the lowest reproductive success and number of pollinators (B. morio workers only).


CONCLUSIONS
Self-fertilization may have evolved in the peripheral population at the highest site of V. caracalla because of the benefits of reproductive assurance under reduced pollinator diversity.
Etcheverry
Angela Virginia
AV
Cátedra de Botánica, Laboratorio de Biología Reproductiva, Facultad de Ciencias Naturales, Universidad Nacional de Salta, Calle Buenos Aires 177, 4400 Salta, Argentina. angelaetcheverry@salnet.com.ar
Alemán
Maria Mercedes
MM
Fleming
Trinidad Figueroa
TF
D000531:Altitude; D000704:Analysis of Variance; D000818:Animals; D001118:Argentina; D001516:Bees / Q000502:physiology; D016009:Chi-Square Distribution; D017753:Ecosystem; D007887:Fabaceae / Q000033:anatomy & histology* / Q000502:physiology*; D035264:Flowers / Q000033:anatomy & histology* / Q000502:physiology*; D005638:Fruit / Q000502:physiology; D007178:Inbreeding; D054817:Pollination; D012639:Seeds / Q000502:physiology