The Amblystegiaceae include pleurocarpous mosses typical of moist, wet, or aquatic habitats. Sporophytes are uniform, and genera are distinguished by the habit, arrangement, and anatomy of leaves, leaf cell shape, and costal structure. Generic limits are controversial. Species have been shifted from genus to genus, sometimes in or out of other related families. Nucleotide sequences from the Internal Transcribed Spacer region of nuclear ribosomal DNA repeat from 39 accessions were analyzed to test monophyly of the genera Amblystegium, Campylium, and Drepanocladus. Reconstructions constrained to support monophyly of each genus were significantly less parsimonious and less likely than from unconstrained searches. ITS sequences support previous suggestions based on morphology that Campylophyllum halleri is not closely related to Campylium stellatum or Campyliadelphus chrysophyllus. Our results also support previous treatments that divide Drepanocladus into two or more segregate genera. Leptodictyum riparium appears more closely related to Campylium stellatum and Campyliadelphus chrysophyllus than to Amblystegium species. Some, but not all, populations of A. humile, Hygroamblystegium tenax, H. fluviatile, and H. varium form a strongly supported clade.
Communicating Editor: Alan Whittemore