Puerto Rico Alfilerillo

Machaonia portoricensis Baillon, Bull. Soc. Linn. Paris 1: 204
1879. A densely branched shrub or small tree, 2-6 meters high, the branches dark-brown, coarsely lenticellate, armed with numerous stout or slender, opposite or ternate spines, the branchlets reddish-brown, puberulent in lines; stipules minute, cuspidate; leaves mostly ternate, the petioles 2 mm. long or shorter, puberulent, the blades orbicular, rhombic-orbicular, oval, or rhombic-ovate, 7-15 mm. long, 5-12 mm. wide, sometimes broader than long, rounded to obtuse at the base, rounded to acute at the apex, usually broadly and acutely short-acuminate, membranaceous or chartaceous, glabrous, slightly paler beneath, the lateral nerves subimpressed, 2 or 3 on each side, the venation reticulate; inflorescence fewor many-flowered, 1-3.5 cm. wide, usually dense, the flowers sessile or short-pedicellate, the bracts often large and foliaceous; calyx and hypanthium 2-3 mm. long, densely short-pilose, the hypanthium turbinate, the 4 calyx-lobes oblong, obtuse or acute, about as long as the hypanthium, much shorter than the fruit; corolla white, 3-3.5 mm. long, glabrous outside, the lobes oval, half as long as the tube; anthers exserted; fruit turbinate, 3 mm. long, densely short-pilose.
Type locality: Puerto Rico.
Distribution: Rocky woods and thickets at lower elevations, western and southwestern Puerto Rico.