The leaves of all plants in the plane family are simple, deciduous, palmate, and somewhat maple-like in appearance. The leaves are palmately veined and have three to nine lobes, depending on the species. The leaves arise from a long petiole (stalk) which is swollen at its base on the twig. The leaves arise alternately on the stem (rather than opposite one another) and the twigs have a characteristic zig-zag appearance.
The flowers of all species are unisexual in that they contain either male organs or female organs, but not both. All species are monoecious, in that male and female flowers arise from the same individual tree. The flowers are minute and arise in large spherical clusters.
The fruit is a characteristic spherical cluster of small, one-seeded, dry, indehiscent fruits, referred to as achenes. Depending on the species, one to several of these spherical fruit clusters arises from a single long peduncle (stem) which is attached to the twig. The small seeds are wind dispersed.
The best known tree of this family is the American sycamore. Its fruit balls are about 1 in (2.5 cm) in diameter and consist of several hundred seeds densely packed together. Naturalist and writer Henry Thoreau eloquently described the seeds of this species as "standing on their points like pins closely packed in a globular pin-cushion, surrounded at the base by a bristly down of a tawny color, which answers the purpose of a parachute."