a. Pertaining to, or resembling, a natural order (Orchidaceae) of endogenous plants of which the genus Orchis is the type. They are mostly perennial herbs having the stamens and pistils united in a single column, and normally three petals and three sepals, all adherent to the ovary. The flowers are curiously shaped, often resembling insects, the odd or lower petal (called the lip) being unlike the others, and sometimes of a strange and unexpected appearance. About one hundred species occur in the United States, but several thousand in the tropics.