Each of the 3,000 species of palm can be distinguished by five major anatomical structures: the stem, leaves, flowers, fruit and seeds. According to Sun Palm Trees, palms first appeared in the fossil record 80 million years ago, and their relatively long evolutionary history has permitted them to develop a much wider internal diversity than younger plant groups.
Palm tree stems are generally straight and circular in cross section, though Sun Palm Trees notes that some species' trunks flare at the base to create a conical shape. These trunks do not support branches at lower levels and are either smooth or covered in the broken-off stumps of old leaves that have been shed. Palm leaves are diagnostic of the palms' family relationships, with palmate leaves erupting in a fan pattern from a common stem and pinnate leaves arranged along a central axis in a feather-shaped pattern. Palm flowers are generally small and greenish, making them difficult to notice. Palms are generally unisexual, though some individual trees will vary their male and female blossoms annually. Seeds take many forms among palms, from the small, soft date to the large, hard coconut. Palm seeds always contain a large mass of endosperm, such as the "meat" of the coconut, and a relatively small embryo within.