Pollination: self-fertilization strategy in an orchid.

Mating in flowering plants normally relies on animals, wind, gravity or secretion to convey pollen grains from the male (anther) to the female (stigma) organ. Here we describe a new type of self-pollination mechanism in the tree-living orchid Holcoglossum amesianum, in which the bisexual flower turns its anther against gravity through 360 degrees in order to insert pollen into its own stigma cavity - without the aid of any pollinating agent or medium. This mode of self-pollination, which occurs under windless, drought conditions when insects are scarce, adds to the variety of mechanisms that have evolved in angiosperms to ensure their reproductive success.