The Collaborative International Dictionary of English v.0.48:

Plane \Plane\, n. [F., fr. L. platanus, Gr. ?, fr. ? broad; --
   so called on account of its broad leaves and spreading form.
   See Place, and cf. Platane, Plantain the tree.] (Bot.)
   Any tree of the genus Platanus.
   [1913 Webster]

   Note: The Oriental plane (Platanus orientalis) is a native
         of Asia. It rises with a straight, smooth, branching
         stem to a great height, with palmated leaves, and long
         pendulous peduncles, sustaining several heads of small
         close-sitting flowers. The seeds are downy, and
         collected into round, rough, hard balls. The Occidental
         plane (Platanus occidentalis), which grows to a great
         height, is a native of North America, where it is
         popularly called sycamore, buttonwood, and
         buttonball, names also applied to the California
         species (Platanus racemosa).
         [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Buttonwood \But"ton*wood`\, n. (Bot.)
   The Platanus occidentalis, or American plane tree, a large
   tree, producing rough balls, from which it is named; --
   called also buttonball tree, and, in some parts of the
   United States, sycamore. The California buttonwood is
   Platanus racemosa.
   [1913 Webster]

WordNet (r) 3.0 (2006):

Platanus racemosa
    n 1: tall tree of Baja California having deciduous bark and
         large alternate palmately lobed leaves and ball-shaped
         clusters of flowers [syn: California sycamore, Platanus
         racemosa]