XXIV. ZYGOPHYLLACEÆ.
Trees or shrubs, with hard resinous wood, and opposite pinnate leaves, with stipules. Flowers perfect, regular; calyx 5-lobed, the lobes imbricated in the bud; petals as many as the calyx-lobes, imbricated in the bud, hypogynous; stamens twice as many as the petals, hypogynous; filaments distinct; anthers introrse, 2-celled, the cells opening longitudinally; ovary 5-celled; styles united, terminating in a minute 5-lobed or entire stigma; ovules numerous, suspended, anatropous; raphe ventral. Fruit capsular, angled or winged, separating at maturity into 5 indehiscent carpels. Seeds solitary or in pairs in each cell; seed-coat thick and fleshy; embryo straight or nearly so; cotyledons oval, foliaceous; radicle short, superior.
Of the fourteen genera of this family, mostly confined to the warmer parts of the northern hemisphere, one only, Guaiacum, has an arborescent representative in the United States.