Habitat: Forming mats on rock, seawalls, mangrove prop roots. Distribution: Florida, Bahamas, Greater Antilles, Lesser Antilles, Southern Caribbean, Western Caribbean, Gulf of Mexico Characteristics: Matt forming prostrate thallus is black to purple (Image 1). Pinnate branching with incurled apices (Image 2). Several layers of cortication surround 6-8 pericentral cells. Tetrasporangia formed in stichidia at brachlet apices.