Orchids are a large and varied family of flowering plants, recognized for blooms with bilateral symmetry and a specialized petal called a labellum, or lip, which often helps guide pollinators. Their reproductive parts are joined in a central structure called a column. Orchid species differ widely in flower shape and color, and examples here include red, white, and yellow blooms. Many tropical orchids grow attached to tree branches as epiphytes, using their roots to anchor themselves and absorb moisture from the air and rain; they do not take nutrients from the trees. Other orchids grow on the ground. Together, these traits make orchids a distinctive group within flowering plants, with varied forms and adaptations to different habitats.