A major pest, the psyllid, has infested leucaena stands around the world with particular susceptibility expressed by varieties of Leucaena leucocephala . Research, however, has identified psyllid-tolerant varieties and hybrids, and psyllid populations in leucaena stands are declining over time, apparently due to natural agents. Not until the 20th century did other species attract interest. Today we recognize 13 species in the genus, and expert others to be validated. Leucaenas vary widely in leaf and tree shape, ranging from shrubs to stately trees.
Leaves are alternate and bipianately compound.
Clustered vertical brown pods, 8-25 cm in length, are a distinguishing mark. LEUC and tetraploid varieties of DIVE are self-pollinating, while all others are outcrossing. Leucaenas are associated with soils of pH 5-8, and are not found on waterlogged soils. The leucaenas fail on highly acid soils, where aluminum completes with calcium and other cations for exchange sites in the soils. The genus is considered an interbreeding complex, and breeding efforts are concentrated on producing interspecific hybrids.