Propagula

Propagula in the Pottiaceae are generally borne on stalks arising from the axils of cauline leaves (e.g. some species of Barbula (Pl. 43, f. 20; 44, f. 10), Didymodon, and Hyophila), but species with propagula borne on long rhizoids buried in the soil are also common (e.g. species of Barbula, Chenia and Tortula). Less frequently, propagula may be born on the tips or margins of leaves (e.g. Streptopogon spp., Pl. 41, f. 12–14; 42, f. 17), on the ventral surface of the costa (e.g. Didymodon spp., Syntrichia rigescens (Pl. 110, f. 19), Trichostomum tenuirostre), and on a naked branch (e.g. Leptodontium stoloniferum, Pl. 37, f. 7). My report of propagula in a cup at the apex of a leaf (Leptodontium stellaticuspis, Zander 1972) is incorrect; the cup apparently produces only rhizoid initials. Rhizoids are also commonly produced at unmodified leaf tips of Leptodontium viticulosoides and Didymodon occidentalis. Long-elliptical propagula of species of Streptopogon have longitudinal internal walls (Pl. 41, f. 16); similarly shaped propagula of species of Calymperaceae lack longitudinal internal walls.

Unicellular propagula are rather rare in the Pottiaceae, to date having been found in Bryoerythrophyllum inaequalifolium (Pl. 24, f. 8; Zander 1968), Didymodon revolutus (Zander 1981c), and Didymodon perobtusus (Zander 1978e). The three species are curiously similar in their small stature and broadly obtuse, elliptical to ovate leaves, among other characters, and may be products of convergent evolution. The fine nature of the diaspores is a possible adaptation for non-sexual long-distance dispersal or local saturation of a large and homogeneous habitat.

Whitehouse (1980) discussed both the literature and provided his own observations on gemmae produced directly on the protonema of many species of Pottiaceae. To date, such protonemal propagula are known for species of the pottiaceous genera Barbula, Desmatodon, Didymodon, Eucladium, Gyroweisia and Tortula, and may well be a common occurrence in hygric habitats.

Sexuality

Terminology for sexuality in the mosses is discussed at length by Lewis (1961), Zander (1984) and Wyatt (1985), among many others. Wyatt (1985) proposed a terminology for bryophytes reflecting the great variation in sexual condition in this group. Unfortunately, Wyatt indicated that, although distinguishing between haploid and diploid sexuality was important, this could ascertained by “context.” This is surely insufficient, being a source of confusion when discussing sexuality in general. Allen and Magill (1987) have published a good response to Wyatt's article, emphasizing the need for a separate terminology for bryophytes. The Wyatt system is recommended here as it nicely parallels the terminology used for angiosperms but with the use of “‑oicous” endings (to indicate gametophyte sexuality) (see Zander 1984 for a review of the history of “‑oecious” and “‑oicous” endings in bryophyte terminology).

Perichaetia

The perichaetial leaves of the Pottiaceae may be similar to those of the remainder of the plant, or differentiated, and sheathing the inner perichaetium (and ultimately the basal portion of the seta) to various degrees. The basal cells of differentiated perichaetial leaves of Pottiaceae taxa are generally elongate and rectangular with a small percentage of cells having tapering, blunt ends. They are seldom prosenchymatous (i.e., with tapering, pointed proximal and distal ends). They may have thickened, porose walls (e.g. Trachyodontium) or thin walls (e.g. Bryoerythrophyllum spp.).

Perigonia

Perigonia (Pl. 1, f. 8; 15, f. 18; 16, f. 9, 16; 18, f. 9; 38, f. 9) are generally bud-shaped in the Pottiaceae, occasionally flattened. Some species have swollen, nearly spherical perigonia with tightly appressed bracts, while some others have perigonia that are small and loosely foliate, thus often difficult to find on gross examination. The perigonia occur terminally or laterally on entirely perigoniate plants, or laterally in the axils of the leaves of sporophyte-bearing, monoicous plants, in which case they are sometimes flattened.