Rhodachlya madagascarensis gen. et sp. nov.: a distinct acrochaetioid represents a new order and family (Rhodachlyales ord. Nov., Rhodachlyaceae fam. Nov.) of the Florideophyceae (Rhodophyta)

A filamentous 'acrochaetioid' red algal epiphyte on Posidonia from Madagascar was isolated into culture. It reproduces solely by monosporangia and the spherical spores have gliding motility that differs from amoeboid spore motility seen with time-lapse video microscopy in most Acrochaetiales and Colaconematales. Electron microscopy reveals that a peripheral encircling thylakoid is absent in the chloroplast, Golgi bodies are associated with mitochondria, and pit plugs have platelike outer and inner caps and lack a cap membrane. Low-molecular-weight carbohydrates are floridoside and trehalose. Molecular evidence (small subunit, large subunit and EF2 sequences) resolved this taxon as a completely novel lineage of the Nemaliophycidae, and it is here described as Rhodachlya madagascarensis J.A. West et al., gen. et sp. nov. In light of the unusual combination of ultrastructural features and the lack of affinity to any of the currently recognized families and orders in molecular analyses, this alga forms the basis of a new family, Rhodachlyaceae G.W. Saunders et al., fam. nov., and order, Rhodachlyales G.W. Saunders et al., ord. nov., of the subclass Nemaliophycidae.