Leguminosae (Fabaceae) the Legume Family; subfamily Mimosoideae, Mimosa and relatives
This deciduous shrub or small tree to 25 feet tall has an open, spreading crown and smooth, pale gray-brown bark. The leaves are twice-pinnately compound, to about a foot long, with four to nine pairs of pinnae (main divisions), and usually a dimple-like gland on the rachis (main axis) between the lowermost pair. The leaflets, with a pointed tip and an uneven base, are small (about 1/2 inch long and 1/8 inch wide) and numerous, with 13 to 17 pairs per pinna. The flowers are tiny, white or pale yellowish, in dense ball-like heads about 3/4 inch in diameter. The fruits (pods) are flat, rounded or blunt at the tip or with a short, broad point, 5 to 7 inches long and an inch or less wide, and reddish brown when mature, with 10 to 20 flattened seeds.
The lead tree is native to Mexico and Central America, but it is cultivated throughout the tropics, and it has widely escaped and naturalized. In the United States, it has been reported from Arizona, California, Florida, Hawaii and Texas.
Lead tree has been collected in disturbed flatwoods, spoil areas, roadsides, and other, mostly weedy sites, in scattered counties from Alachua County to the Keys (Monroe County).
The foliage is remarkably similar to that of the mimosa (Albizia julibrissin), but the foliar gland of the lead tree, if present, is located on the rachis of the leaf between the lowermost pair of pinnae, while that of the mimosa is located near the base of the petiole. The fruit (pod) of the two species is also very similar, but that of the lead tree is usually blunt at the tip, or with a short point, while that of the mimosa is usually more tapered at the tip, with a longer, more slender point. The flowers of the two are very different. Those of the mimosa are pink and are borne in loose, open heads, while those of the lead tree are white or yellowish and are borne in tight, ball-like heads. Seedlings might be confused with the partridge pea (Chamaecrista fasciculata), but that plant has once-pinnate leaves, and much larger, solitary, golden yellow flowers.
The abundantly produced seeds are the only effective means of dispersal. The light, flat pods are readily blown about by the wind.
The tree is frost-sensitive, and, except in very protected sites, it is killed to the ground during most winters in northern Florida. However, regrowth is rapid and most trees recover sufficiently to produce large crops of seeds. The seeds germinate readily without pre-treatment, and large numbers of seedlings have been observed around mother plants. In the tropics, where the lead tree is still widely grown as a green manure and forage crop, it has become an invasive weed, due in part to its rapid growth, high drought tolerance, and prolific seed production. Leucaena leucocephala is listed as a Category II Invasive by the Florida Exotic Pest Plant Council (FLEPPC), and it has been added to the list of noxious weeds by the state of Florida (Rule 5B-57.007, F.A.C.). Two subspecies, both regulated, are found in Florida: the shrubby subsp. leucocephala and the treelike subsp. glabrata.