Towards a revision of the moss genus Taxithelium (Sematophyllaceae)

Abstract

IN RELATION TO AN ONGOING TAXONOMIC REVISION OF THE ESSENTIALLY TROPICAL MOSS GENUS TAXITHELIUM SPRUCE EX MITT., THE CHARACTES USED TO CIRCUMSCRIBE THE GENUS AND THOSE USED TO SEPARATE THE SPECIES ARE BEING EVALUATED. THE DISTRIBUTION OF THE GENUS IS ALSO BEING ASSESSED. TRADITIONALLY, TAXITHELIUM HAS BEEN CHARACTERISED BY THE SERIALLY ARRANGED PAPILLAE OVER THE LUMEN OF THE LAMINAL CELLS AND THE MORE OR LESS QUEDRATE ALAR CELLS. HOWEVER, CRITICAL OBSERVATIONS ON MORPHOLOGY, INCLUDING THOSE MADE WITH SCANNING, SUCH AS TYPE OF BRANCH DEVELOPMENT, THE PAPILLOSE-SERRATE MARGINS OF THE LEAVES AND THE PAPILLOSITY OF THE PERICHAETIAL LEAVES. THESE CHARACTERS HAVE PROVED TO BE USEFUL IN DISTINGUISHING TAXITHELIUM FROM CLOSELY RELATED GENERA, WHEREAS CHARACTERS OF THE RHIZOIDS, CALYPTRA, VAGINULA, AND EXOTHECIAL CELLS ARE FOUND TO BE HELPFUL IN SEPARATING SOME OF THE SPECIES WITHIN THE GENUS. THE GENUS TAXITHELIUM EXTENDS ALL OVER TROPICAL REGIONS, WITH A SLIGHT INTRUSION INTO THE SUBTROPICS, OCURRING BETWEEN APPROXIMATELY 30º N AND 20º S LAT. THE WIDE DISTRIBUTION OF THIS GENUS IS LARGELY DUE TO THE VERY VARIABLE SPECIES T.PLANUM (BRID.) MITT, WHICH OCCURS FROM THE SOUTHERN TIP OF FLORIDA SOUTHWARDS THROUGH CENTRAL AMERICA AND THE WEST INDIES TO BOLIVIA; ON THE AFRICAN CONTINENT IN CONGO, ANGOLA, CAMEROON, GABON, GUINEA AND LIBERIA; THROUGHOUT TROPICAL ASIA AND IN THE NORTHERN TERRITORY OF AUSTRALIA. THE LARGEST CONCENTRATION OF SPECIES IS FOUND IN MALESIA.