A Taxonomic Revision of the Monocaul Phanerophyte Ardisia (Primulaceae) of Gabon

Monocaul Ardisia (Primulaceae) have a single, vertical, woody stem and spiral phyllotaxy. They range from 30 cm to 100 cm tall. Three species of this architectural group, Ardisia mayumbensis, A. hallei and A. bracteata, have been recorded from Gabon hitherto. In this taxonomic revision we show that A. mayumbensis does not occur in Gabon, and we describe three new species. Two of these, Ardisia doudou sp. nov.and A. mica sp.nov., are endemic to Gabon and one, A. litterbin sp.nov, is found in both Gabon and Republic of the Congo. Ardisia hallei and A. bracteata are redescribed. All five species have a litter-gathering habit with a terminal funnel of leaves, and two of these species, Ardisia doudou and Ardisia litterbin, also possess adventitious roots in the distal part of the stem, a well-established strategy found in litter-gathering forest species of other plant families in tropical Africa. We provisionally assess the conservation status of all five taxa using the 2012 IUCN standard, finding that all monocaul Ardisia in Gabon fall within threatened categories. Two of the species, Ardisia bracteata and A. mica, are known from single collections and have not been seen for 164 and 63 years respectively and are conceivably extinct although further surveys are needed to establish this. We employ new characters in delineating and describing African Ardisia using leaf thickness and oil gland data.