Phenology and Reproductive Biology of Syntrichia inermis (Bryopsida, Pottiaceae) in the Mojave Desert

Abstract

Six populations of Syntrichia inermis (Brid.) Hueb. from the Nevada Mojave Desert were sampled every two weeks for a period of one year. Stem elongation rates were very low (0.14 mm yr. -'), with vegetative growth occurring during the winter. Plants were gonioautoicous, with >90% of the plants morphologically bisexual; however, functionally female stems outnumbered functionally male stems. Archegonia were initiated and became receptive in the same winter, whereas antheridia were initiated in the winter and took from one to several years to reach maturity. On an inflorescence basis, the number of archegonia was fewer and less variable than the number of antheridia, with the abortive rate 3-4% for both gametangia. Fertilization occurred during winterlearly spring, with 50% of the current cycle perichaetia becoming fertilized. Embryos were essentially dormant from spring through fall, resuming growth the following winter, when seta elongation and capsule expansion occurred. A protracted late operculum intact phenophase occurred, with spore dispersal beginning in late summerlearly fall. Previously unknown phenological/reproductive features reported for S. inermis include the lowest known rates of stem elongation, gametophytic and sporophytic growth restricted to winter, the longest period of antheridial maturation, a new pattern of antheridial maturation, and a sporophyte maturation pattern that includes 18 + months of dormancy. Phenological studies of mosses began with broad surveys of local floras (e.g., Grimme 1903) and progressed to detailed studies of single species (e.g., Longton & Green 1969). Perhaps the most significant breakthrough in this field occurred when the stages in the life cycle were defined and quantified (Greene 1960). Since then, the dynamics of vegetative growth, gametangial maturation, stem architecture, and sporophyte life history have been presented for a variety of species (e.g., Deguchi & Takeda 1986; Hancock & Brassard 1974; Imura & Iwatsuki 1989; Longton 1979; Miles et al. 1989; Stark 1986; see review in Longton 1990). Such studies often provide data relevant to the evolution of breeding systems, the allocation of resources to sexual reproduction, and the division of effort between sexual and asexual reproduction. The life history features of desert mosses are not well known (Longton 1988; Scott 1982). It is sometimes assumed that bryophytes in the desert are primarily annuals, escaping the heat and dryness by contracting the life cycle into a few months. However, studies on the desiccation resistance of species in the Syntrichia ruralis (Hedw.) Web. & Mohr complex indicated that some species are perennial and able to withstand desiccated conditions for long periods of time without incurring irreparable cellular damage (Bewley 1979; Oliver et al. 1993). Nevertheless, photosynthesis is restricted to periods when the gametophyte is hydrated (Alpert 1979), which are short and intermittent in the American deserts. The phenology of two species in the Pottiaceae has been studied from the Chihuahuan Desert of New Mexico, S. ruralis and Trichostomum sweetii (Bartr.) Stark (as T. perligulatum (Flow.) Zand.). Both of these species were found to be perennial, but differed from one another in several respects. Gametangia were matured in the fall in T. sweetii, vs. the summer for S. ruralis (Mishler & Oliver 1991; Stark & Castetter 1995). In addition, annual stem elongation rates were much higher in S. ruralis, the populations of which were all female and at a higher elevation. Syntrichia inermis [= Tortula inermis (Brid.) Mont.] is known from throughout the American southwest and adjacent Mexico (Flowers 1973; Mishler 1994). This species is common at middle to low elevations in the Mojave Desert, and is a dominant species on soil below 760 m. It is a distinctive species, recognized by the coiled leaves when dry (into a sickle-shape with half the lamina lying horizontal; Weber 1973), autoicous condition, leaf margins recurved from base to apex, leaf apices mucronate, and sporophytes nearly always present (for illustrations see Flowers 1973, p. 203; Mishler 1994, p. 329). When dry, gametophytic plants of S. inermis resemble those of Tortula atrovirens (Sm.) Lindb. [= Desmatodon convolutus 0007-2745/97/13-27$1.6510 This content downloaded from 207.46.13.128 on Tue, 06 Sep 2016 05:44:12 UTC All use subject to http://about.jstor.org/terms 14 THE BRYOLOGIST [VOL. 100