Rubia agostinhoi has branched, glabrous, brushed or smooth stems, up to long. It has narrowly elliptical to linear or oblanceolate leathery, dark green leaves with very small, slightly revolted spines in the margins. Leaves of the side shoots are shorter and smaller in length than those of the main stem. Flower stems are long and usually very flowery. Fruits are, globose and shinyblack when ripe.