Any member of the family Orchidaceae, the second largest plant family after the composites, consisting of around 18,500 species occurring in nearly all parts of the world but most abundant in tropical rainforests, where they mostly grow as epiphytes. Orchids have flowers of complex structure, with bilateral symmetry and elaborate pollination mechanisms. Their seeds are the smallest of any flowering plant seeds, sometimes a million or more present in the one capsule, and contain no stored plant food. The growth of orchids depends on a symbiotic fungus in their fleshy roots.