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Published In: Bryologia Germanica 1: 112. 1823. (Bryol. Germ.) Name publication detail
 

Project Name Data (Last Modified On 2/15/2011)
Acceptance : Accepted
Project data     (Last Modified On 2/15/2011)
Discussion:

Gymnostomum, a genus of 20 species (Crosby et al. 2000), is found on rocks, boulders and cliff faces usually in wet or seepy places. It is generally associated with calcareous habitats but also occurs occasionally on acidic rocks. The genus usually is soft-green in color, has lanceolate leaves with plane leaf margins that are roughened papillose above and at times serrulate below. Its stem has a central strand and at times a weakly developed hyalodermis is present. The leaf cells in Gymnostomum are firm-walled throughout and are ornamented by simple, low, scattered papillae. Although most members of Gymnostomum have two stereid bands in the costa, Central American collections of G. aeruginosum have only a single (dorsal) stereid band. The perigonia and perichaetia are terminal in Gymnostomum and its capsules are eperistomate.

Zander (1993) considered Gymnostomum a reduced, hydrophilic segregate of Barbula. The genus however is often associated with Hymenostylium recurvirostrum. Zander (1993) puts Gymnostomum and Hymenostylium in different tribes on the basis of whether or not a stem central strand is present. Some forms of Molendoa can be difficult to distinguish from Gymnostomum. Usually the two genera can be distinguished by the percurrent to excurrent costa, massive leaf papillae and lateral perichaetia of Molendoa. Zander (1977) provided an in-depth treatment of the genus in Middle America.


 

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Gymnostomum Nees & Hornsch., Bryol. Germ. 1: 112. 1823, nom. cons.

Gymnostomum Hedw., 1801, nom. rejic

Plants small to medium-sized, light- to dark-green above, brown below, often crusted with calcareous deposits, in tufts or cushions. Stems erect, sparsely and irregularly branched, sclerodermis present or absent, hyalodermis present or absent, central strand present; rhizoids dimorphic: slender, red, smooth, branched ones scattered on the stem and massive, red, roughened, sparsely branched ones originating in leaf axils. Leaves ligulate to linear-lanceolate, plane or weakly concave above, wide‑spreading when wet, appressed when dry; apices contorted, acute to obtuse or sometimes rounded; margins plane, entire to crenulate; costae ending below apex, narrow, dorsal surface papillose, ventral surface papillose, guide cells present, ventral stereid band present or absent, dorsal stereid band present, ventral surface cells enlarged, dorsal surface cells smaller than laminal cells and strongly thickened; laminal cells weakly heterogeneous, rounded to quadrate sometimes transversely rectangular, papillose by simple, low papillae, basal cells homogeneous, short-rectangular, smooth. Asexually reproducing by gemmae in leaf axils. Dioicous. Perigonia and perichaetia terminal. Setae elongate. Capsules exserted, erect, short-cylindrical; peristome absent; opercula rostrate. Calyptrae cucullate.

 
 
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