Revision of the madagascan endemic Homollea (Rubiaceae - Pavetteae), with description of two new species

Abstract

Homollea Arènes (Rubiaceae, subfamily Ixoroideae, tribe Pavetteae) is a genus of shrubs and small trees endemic to western and northern Madagascar. The genus comprises fi ve species occurring in dry deciduous forest, often in limestone areas. The fi ve species are narrow endemics and their conservation status is either Endangered (4 species) or Critically Endangered (1 species). Homollea is characterized by few-flowered, pseudo-axillary, pedunculate inflorescences, well-developed calyces with the lobes much longer than the tube, laterally flattened seeds with a shallow, elongated to linear hilum and entire endosperm, ovules arising from the upper margin of the placenta, and, pollen grains with supratectal elements in the shape of microgemmae. Until now, three species were known and their descriptions are amended. Two further species, H. furtiva De Block sp. nov. and H. septentrionalis De Block sp. nov., are described as new for science. The fi ve species are dealt with in detail: descriptions, distribution maps, conservation assessments, illustrations, lists of exsiccatae and an identifi cation key are given.