Trees featuring green pods full of bean-like seeds are most likely members of the legume family (Leguminosae or Fabaceae). Two trees which unite green seed pods with flat brown “beans” are cotton tree or mimosa (Albizia julibrissin), sturdy in U.S. Department of Agriculture plant hardiness zones 6 through 9, and yellowwood (Cladrastis kentukea), growing in USDA zones 4 through 8. Although the two species have similar pods, their flowers and leaves are different.
Both mimosa and yellowwood, which can be tightly associated, bear seed pods reminiscent of bean or pea pods. The pods are thin and fragile when young, but age to a leathery texture. Yellowwood pods are between 2.5 and 4 inches long, green, flattened and segmented so that every seed seems to have its own charming compartment. Silk tree bears seed pods which are longer, around 7 inches, full of flat brown seeds. The pods persist on the trees throughout the winter.
Aside from the duration of the seedpods, among the most notable differences between mimosa and yellowwood is that the configuration of the flowers. Mimosa trees are summer bloomers, with fragrant brush-like pink flowerheads, borne in fantastic profusion. Yellowwood blooms in late spring along with its fragrant flowers, borne in elongated clusters or panicles, are reminiscent of wisteria. The individual flowers are white with a pinkish tinge and the panicles can be around 15 inches long.
Another distinct difference between mimosa and yellowwood trees would be the leaves. Mimosa leaves are dark green, compound, and pinnate or feathery, resembling ferns. They are exceptionally sensitive and curl up when even lightly touched. Yellowwood is characterized by foliage that’s compound, consisting of classes of around eleven leaflets; the person leaflets are oval or teardrop shaped and do not resemble ferns. They are lighter in shade than mimosa leaves and do not share the mimosa leaves’ sensitivity.
Using a height of 30 to 50 feet along with an almost identical spread, yellowwood is bigger than mimosa, which reaches 20 to 40 feet with a virtually identical spread. Yellowwood is an upright tree with a wide, rounded crown, while mimosa comes with a vase-shaped division configuration along with a crown that’s somewhat flattened on top. In the fall, mimosa leaves stay green until they drop in the tree, while yellowwood foliage turns bright yellow. Yellowwood is also distinguished by vibrant yellow heartwood.