El género Hydrolithon Foslie (Corallinales, Rhodophyta) en la costa Atlántica y Caribe de México

This paper provides the first monographic account ofthe genus Hydrolithon Foslie (1909) along theAtlantic and Caribbean coast of Mexico. We found five species of this genus including two new records for this region: H. onkodes (Heydrich) D.Penrose et Woelkerling and H. reinboldii (Weber van Bosse et Foslie) Foslie. The most common species in the study area was H. farinosum (J.V.Lamouroux) D.Penrose et Y.M.Chamberlain. H. onkodes and H. pachydermum (Foslie) J.C.Bailey, J.E.Gabel et D.W.Freshwater were compared with lectotype specimens. All species may be differentiated between them on the basis ofthe next characteristics: 1) Habit: with or lacking protuberances, free or attached; 2) Thallus construction: monomerous or dimerous; 3) Basal region: unistratose or multistratose; 4) Trichocytes: scattered or in horizontal or vertical rows or large pustulous fields; 5) Pore canal cells: shape. Morphological, anatomical and reproductive accounts are provided, including keys, information on distribution, habitat and nomenclature.