The Catagoniaceae are a small, monogeneric family. The family is nearly restricted to the South-ern Hemisphere, where it occurs in southern South America, southern Africa, the Mascarene Islands, New Guinea, Australasia, and the Subantarctic Islands. One species (C. brevicaudatum) extends into the Northern Hemisphere: Colombia, Venezuela, Central America, and Mexico. The family has stems with an outer layer of sclerodermal cells, no pseudoparaphyllia, and mostly unbranched, papillose rhi-zoids that originate from clusters of initials abaxial to the leaf insertions. Its leaves are pseudodistich-ous, concave to asymmetrically conduplicate, and lack alar cell development. The family has hypna-ceous peristomes and cucullate calyptrae. The Catagoniaceae were established by Buck and Ireland (1985) for a group of species previously placed in the Phyllogoniaceae or Plagiotheciaceae. They dif-fer from the Phyllogoniaceae in lacking creeping stolons and pseudoparaphyllia, but having papillose rhizoids, pseudodistichous, strongly concave to asymmetrically concave leaves, and hypnaceous peri-stomes. The Plagiotheciaceae, as narrowly circumscribed by Buck and Ireland (1985), differ in hav-ing leaves with well-developed alar cells that extend into long decurrencies and stems with a distinc-tive hyalodermis. Pedersen and Hedenäs (2001, 2002) greatly expanded the Plagiotheciaceae to include a large number of disparate and clearly unrelated genera. Their studies, however, often aligned Catagonium with Herzogiella, Isopterygiopsis, or Pseudotaxiphyllum, all genera of the Hyp-naceae. Buck and Ireland (1985) separated the Catagoniaceae from the Hypnaceae because of its conduplicate leaves, but the leaves of Isopterygiopsis are just as strongly conduplicate as those of Catagonium.