General: Olive family (Oleaceae). Native trees growing to 20-30 m tall, maintaining a central leader (strong apical dominance) in youth with an even distribution of branches, developing a dense, conical or rounded crown at maturity. The trunk is long, straight, and free of branches for most of its length (except when open grown). The bark is thick, dark gray, with a uniform, diamond-shaped ridge and furrow pattern. Leaves are deciduous, opposite, pinnately compound, 20-38 cm long, leaflets usually 7(5-9), short-stalked, ovate to ovate-lanceolate or elliptic, acuminate, 6-13 cm long and 3-6 cm wide, sometimes with a few teeth near the tip, dark green and smooth above, whitish below. Flowers are numerous, very small, green to purplish, in small branched clusters near the branch tips, usually either male (staminate) or female (pistillate), a single tree usually bearing only one sex (the species dioecious). Fruits are samaras 2.5-5 cm long, hanging in clusters, with a narrow wing extending about 1/3-1/4 of the way down the cylindrical body. The common name is in reference to the white color of the wood.
This species flowers in April-May, the male first, before appearance of the leaves; fruiting August-October, the seeds dispersed September-November. The pollen is already airborne during the 7-10 days when the female flowers are receptive.
Variation within the species: A number of variants have been described within the species, including F. americana var. biltmoreana (Beadle) J. Wright ex Fern. (= F. biltmoreana Beadle) and F. americana var. microcarpa A. Gray, but the distinctions between these have not been generally confirmed and formal variants are not currently recognized. Diploids (2n=46), tetraploids (2n=92), and hexaploids (2n=138) occur within the species, but it is difficult to associate differences in ploidy level with other patterns of variation.
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