At a single locality in the Organ Mountains of southern New Mexico, eight populations (i.e., contiguous clumps of uniform height and appearance) of the dioicous moss Tortula ruralis were marked and sampled approximately every 30 days over a 13-month period for reproductive condition, length of any new branches, and the total length of the shoot that was green. In addition, chlorophyll was extracted and chlorophyll a and b content determined. Significant differences were noted among populations for each of these measures, but the following general patterns were observed: 1a) A distinct annual cycle in growth and reproduction occurred; 1b) the main seasonal pattern of branching was sympodial, by innovation; 1c) new innovations first appeared in midwinter, lengthened slowly through the spring then rapidly in late summer, with growth completed by the winter following appearance; 1d) female gametangia were initiated in midwinter and terminated growth of the innovation on which they occurred; 1e) fresh female gametangia were observed over a 6- to 9-month period from December to June or August; 2) no male gametangia or sporophytes were observed; 3) the amount of green tissue and the total chlorophyll/dry weight ratio were higher in late summer and winter than in early summer; 4) chlorophyll a/b ratios did not vary on any regular annual pattern, in contrast to the situation known in mesic forest mosses; and 5) chlorophyll a/b ratios were relatively low (1.00-2.50 most commonly), as compared to those of tracheophytes.