Passiflora, known also as the passion flowers or passion vines, is a genus of about 500 species of flowering plants, the type genus of the family Passifloraceae. They are mostly vines, with some being shrubs, and a few species being herbaceous. For information about the fruit of the passiflora plant, see passionfruit. The monotypic genus Hollrungia seems to be inseparable from Passiflora, but further study is needed. The passion flowers have a unique structure, which in most cases requires a large bee to effectively pollinate. In the American tropics, wooden beams are mounted very near passionfruit plantings to encourage carpenter bees to nest. The size and structure of flowers of other Passiflora species is optimized for pollination by hummingbirds (especially hermits like Phaethornis), bumble bees, Carpenter bees (Xylocopa varipuncta), wasps or bats, while others are self-pollinating. The sword-billed hummingbird (Ensifera ensifera) with its immensely elongated bill has co-evolved with certain passion flowers, such as P. mixta.