Shrubs or trees; branches spreading or straggling, slightly angled, stout, hairy, becoming glabrate. Leaves opposite or fascicled [sometimes crowded on short lateral branchlets], even-pinnately compound; stipules usually deciduous, sometimes persistent, stiff or herbaceous, subulate or ovate, apex acute to acuminate, usually mucronulate, sometimes spinescent; petiolules absent or nearly so; leaflets [2–](4–)6–16, opposite, distinct, [narrowly] elliptic to linear-oblong, linear-spatulate, obliquely oblong, or obovate [ovate], somewhat unequal in size, basal and middle [apical] pairs largest, base oblique, apex obtuse or rounded [acute or retuse] and mucronate, [membranous] subcoriaceous or coriaceous, surfaces glabrous [hairy to glabrate]. Pedicels in axils of minute bracts [crowded on short lateral branchlets], erect or spreading. Flowers solitary to several [many] together, slightly irregular by twisting of petals; sepals deciduous, 4–5, slightly connate basally, green, unequal, margins undifferentiated, apex obtuse, hairy; petals ± persistent, 4–5, imbricate, spreading, twisted, blue to purple, rarely white [violet], drying yellow, obovate to elliptic, base clawed, apex rounded to lobed or notched; nectary annular; stamens 8–10, ± equal; filaments free, subulate or base slightly winged, sometimes with small basal scale; anthers sagittate or cordate; ovary on short stalk, 2–5-lobed, 2–5-locular, glabrous or hairy; ovules 8–10 per locule; style persisting, forming beak on fruit; stigma minute. Fruits capsules, [green] becoming greenish yellow to bright orange [-brown], obovoid to obcordiform, flattened, 2–5-lobed, 2–5-winged, base narrowed into short stalk, broadest apically, coriaceous, smooth or reticulate, septicidally dehiscent. Seeds 1 per locule, 1–5 maturing per fruit, yellowish brown, brown, or black, ellipsoid to ovoid, surrounded by thick fleshy red aril.
sc, se United States, Mexico, West Indies, Central America, n South America.
Species ca. 6 (2 in the flora).
Guaiacum wood is hard and resinous, long used in turnery and medicine. Several species are grown as ornamentals for their showy flowers in southern Florida, southern Arizona, Mexico, the West Indies, and Central America. Guaiacum officinale Linnaeus is known from Florida not only in cultivation, but also as a local escape; however, it has not become naturalized. It can easily be distinguished from G. sanctum by its leaves having only (2–)4–6 shiny, green, obovate leaflets that are 15–35(–60) × 25–35 mm. The fruits are 2-lobed and contain only 1 or 2 seeds.