Pollination and dispersal

Pollination and dispersal

The biology of the Zingiberaceae is still poorly known. Pollination and dispersal of the seeds have only been observed in few species, but insects, such as butterflies and moths seem to play a major role. Ants and bees have been seen to visit flowers of several Amomum, Alpinia, and Boesenbergia species and are certainly important pollination agents. Birds (spiderhunters and sunbirds) have been observed in Sarawak and Sabah as pollinators in Etlingera and Hornstedtia species with red-flowered inflorescences. The attractive, orange and red flowers of Siamanthus siliquosus, where a drop of nectar is found at the throat in the morning, are probably also pollinated by birds, but that has still to be observed.

In the genus Hedychium, where several flowers open at the same time, butterflies and hawk moths are sometimes seen to be trapped in the long, narrow corolla tubes. In their efforts to free themselves the insects pollinate several neighbouring flowers. The white flowered species open the flowers in the evening, when they also have a strongest scent. Butterfly pollination has also been observed in Etlingera.

In several genera e.g. Curcuma, Roscoea, and Cautleya, the anther is provided with basal spurs. This, combined with a versatile anther, suggests bee pollination. When a bee visits the flower, it will hit the basal spurs which force the anther to tip forward and place pollen on the back of the bee. When visiting the next flower the anther, with the stigma placed on top, will touch on the same place of the insect and pollination will occur. Bee pollination has been observed in Alpinia, Globba and Roscoea.

The dispersal of seeds is even less known. The open capsules of Hedychium are highly orange-coloured on the inner side, and the red arillate seeds, fused into a single mass in the open capsule, seem to invite birds to a meal and thus disperse the seeds, although bird dispersal has never actually been documented.

In Roscoea, after flowering, the whole shoots with the ripe capsules are bending down until they lay prostrate on the soil, where the arillate seeds are presented to the ants for food (the aril). This is a way of ant dispersal also known form other plants with arillate seeds. Many other species, fruiting near the ground, have white, lacerate arils and may be spread by ants. In Etlingera araneosa, in Thailand we have observed that the large, fleshy fruits have been gnawed at the top and emptied for seeds by small rodents, similar observations have been done in Sabah by A. D. Poulsen (personal communication). In the genus Caulokaempferia most of the yellow flowered species, found along streams, seed dispersal by rain splash or splash from the nearby streams has been observed. The seeds are minute, without aril but with a dense cover of short hairs. Their pubescence will form an airy layer around the seed which keep them floating.