Populations of the desert moss, Syntrichia caninervis, were sampled approximately every four weeks, and/or immediately following significant hydration events at Red Rock National Conservation Area, Las Vegas, Nevada, USA. Samples were collected from 12 populations (4 exclusively female, 4 mixed sex, and 4 exclusively male) over a period of more than two years, from the fall of 1998 to the spring of 2001. Collections were made using random coordinates on a grid to allow mapping of population structure. During dissection, the presence of distinct annual growth intervals permitted assessment of stem elongation, quantification of gametangial initiation and maturation, and determination of maturation indices for recent gametangia. Sporophytes were initiated, but not matured, in both the spring of 1999 and 2000, and hence, we will not report on sporophytic maturation. Stem elongation rates varied, apparently dependent on microsite differences. Stems within the main portion of the cushion elongated at approximately 0.3 mm per year, and stems on the edges of the cushion or in the open elongated at less than 0.2 mm annually. On average, growth intervals which contained gametangia consisted of either a perichaetium with 4-5 archegonia or a perigonium with 14 antheridia. Archegonia were initiated in the fall of 1998 and became receptive spring of 1999. Antheridia initiated at the same time matured to half their full size by the end of spring, were dormant during the summer of 1999, and did not disperse sperm until spring 2000. A few antheridia were completing maturation and dispersal of sperm into spring 2001. Based on previous studies of desert moss phenology, gametangial maturation, fertilization, and probably sporophyte maturation occur during the cooler, moister fall through spring months in the Mojave desert.

Key words: gametangial maturation, growth rate, phenology, Syntrichia caninervis