Chinese biologists have made the first discovery of a plant that pollinates itself. Holcoglossum amesianum, a tree-dwelling orchid, works against gravity to place pollen from its male appendage (the anther) to the female cavity (stigma). Most flowers depend on natural forces (wind, gravity) or insects for pollination.
K.W. Liu et al. 2006. Pollination: Self-fertilization strategy in an orchid. Nature 441: 945-946.