A new species of Colletoecema (Rubiaceae) from southern Cameroon with a discussion of relationships among basal Rubioideae

Colletoecema magna, a new species from the Ngovayang Massif (southern Cameroon) is described and illustrated. A comparative morphological study illustrates the similar placentation and fruit anatomy of the novelty and Colletoecema dewevrei, the only other species of the genus. Colletoecema magna essentially differs from C. dewevrei by its sessile flowers and fruits, the corolla tube that is densely hairy above the insertion point of the stamens and the anthers that are included. Further characters that separate the novelty are its larger leaves, more condensed inflorescences, and larger fruits. Its position within Colletoecema is corroborated by atpB-rbcL and rbcL chloroplast sequences. The relationships among the basal lineages of the subfamily Rubioideae, to which Colletoecema belongs, are briefly addressed. Based on our present knowledge, a paleotropical or tropical African origin of the Rubioideae is hypothesized.