An orchid that flowers in harsh conditions pollinates itself unassisted by any of the usual agents. Mating in flowering plants normally relies on animals, wind, gravity or secretion to convey pollen grains from the male (anther) to the female (stigma) organ1. Apart from that, a new type of self-pollination mechanism in the tree-living orchid Holcoglossum amesianum, is observed in which the bisexual flower turns its anther against gravity through 360° 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.
Almost two thousand H. Amesianum flowers were studied over three flowering seasons in forests in the Yunnan province of China. Each flower has a beak-like projection, known as the rostellum, which separates the anther, the male organ of the flower, from the female stigma cavity. During self-pollination, the anther extends itself downward beyond the rostellum and then thrusts itself upwards to insert pollen into the stigma cavity. All of the flowers were found to use this strategy, and over half succeeded at self-pollination with almost all of these going on to bear fruit.
Source: http://www.nature.com/nchina