Mitracarpus maxwelliae, of the family Rubiaceae, was discovered on March 8, 1925, by Nathaniel L. Britton on a limestone hill in the municipality of Guánica, Puerto Rico. The site was later rediscovered by Alain Lioger in 1982 and again by George R. Proctor and Miguel Canals in 1987. M. maxwelliae is a low, densely-branching, moundlike shrub which may reach approximately 20 centimeters in height. The somewhat woody branches are striate and sharply 4-angled. The leaves are opposite, sessile, linear or linear-lanceolate, densely scabrous, and from 1 to 3 centimeters long and 2 to 5 millimeters wide. The flower heads are terminal, dense, sub-globose, and from .8 to 1.3 centimeters in diameters. The corolla is white, narrowly funnelform, minutely glandular-papillose, and 5 ro 6 millimeters long. The capsule is about 1.5 millimeters in diameter, opening by a transverse circular split at about the middle. The seeds are ellipsoid, brownish-black, and 1.2 millimeters long and .8 millimeters wide (Proctor 1991).