AN ECOLOGICAL STUDY OF SEXUAL REPRODUCTION IN SOME TROPICAL HERBACEOUS SPECIES

摘要

Four herbaceous species, namely, lndigofera linnae (Fabaceae: Faboideae), Evolvulus alsinoides, Evolvulus nummularius and Merremia tridentata (Convolvulaceae: Convolvuloideae) were studied with reference to their phenology, floral biology, sexual system, pollination, fruiting behavior and seed dispersal. /. linnae is monostylous, bisexual, weakly protandrous and self-compatible. The flowers are characterized by papilionaceous corolla with stamens and stigma concealed by its keel petals and escorted laterally by wing petals and above by standard petal. They possess explosive pollination mechanism in which the keel petals require tripping to expose the sex organs and achieve pollination. The abiotic and biotic agents trip the keel petals; the former category affects only self-pollination while the latter category affects both self- and cross-pollination. The abiotic agents include high winds, heavy rain and high temperature while biotic agents are bees and lycaenid butterflies of which bees are efficient to trip the pollination mechanism. Thrips use the flower buds for breeding and emerge during anthesis; then they pollinate the flowers by feeding on pollen and nectar due to which the availability of floral rewards is reduced after anthesis. The plant is facultatively autogamous". The fruit is a pod which dehisces explosively to disperse seeds; long distance dispersal is facilitated by their irregular shape and oily nature and carried away by wind and rain water. E. alsinoides and E. nummularius are monomorphic, distylous, bisexual, weakly protandrous and self-compatible. They are facultatively xenogamous. Both the species during open state of flowers are pollinated by honey bees and lycaenid butterflies; E. alsinoides is additionally pollinated by small carpenter bee while E. nummularius is also pollinated by stingless bees. Ballistichory, anemochory and hydrochory are the functional modes of seed dispersal. M tridentata is bimorphic, monostylous, bisexual, weakly protandrous and self-compatible. Theplant is highly self-compatible and obligately autogamous. The flowers are pollinated by honey bees, stingless bees and lycaenid butterflies. A neogastropod snail, Euplecta subdecussata feeds on the corolla, stamens and stigma tips of this plant, the feeding which has negative effect on the sexual reproduction of the plant. Ballistichory, anemochory and hydrochory are the functional modes of seed dispersal.