Monographs Details: Anthacanthus spinosus (Jacq.) Nees
Authority: Britton, Nathaniel L. Flora Borinqueña.
Description:Species Description - This is one of the most spiny bushes in the West Indian flora, sometimes forming thickets difficult to penetrate, attractive, however when in bloom, by its often profuse, violet to purple flowers. It is frequent at lower and middle elevations in Porto Rico, often in rocky places, inhabiting both moist and dry districts, and ranges widely through the West Indies. It is the type species of its genus, first made known botanically from Martinique, and is the only one inhabiting Porto Rico.
Anthacanthus (Greek, spiny-flower) is a West Indian genus of about 6 species of small-leaved, armed shrubs, the leaves opposite, the small, stalked flowers borne solitary or fascicled in their axils. The calyx is 5-cleft; the corolla has a slender, nearly cylindric tube, and a spreading, unequally 5-lobed limb; there are 2 perfect stamens with short filaments and oblong anthers, and two imperfect ones (staminodes); there are 2 ovules in each cavity of the 2-celled ovary, and the style is slender. The fruit is an oblong, stalked capsule, splitting elastically into 2 valves when mature, releasing the 4, or fewer, tubercled or wrinkled seeds.
Anthacanthus spinosus is an upright or diffuse shrub, about 2 meters high, or usually lower, with slender, smooth or hairy branches, armed with stiff, more or less recurved spines from 4 to 12 millimeters long. Its leaves are short-stalked, firm in texture, from 3 to 20 millimeters long, various in form, pointed, blunt, or notched, with a rather prominent midvein, but obscure lateral veins. The flower-stalks are from 6 to 10 millimeters long, the calyx 3 or 4 millimeters long; the tube of the corolla is about 8 millimeters long, the oblong lobes of its limb about as long; the style is about 10 millimeters long. The capsule is about 2 centimeters long, the seeds 2 or 3 millimeters in diameter.
Justicia spinosa Jacquin. Enumeratic Systematica Plantarum 11.1760.
Anthacanthus spinosus Nees, in De Candolle, Prodromus 11: 460. 1847.