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

Project Name Data (Last Modified On 10/24/2011)
Acceptance : Accepted
Project data     (Last Modified On 10/24/2011)
Nomenclature:

34. GYMNOSTOMUM                 Plate 46.

Gymnostomum Nees & Hornsch., Bryol. Germ. 1: 112, 1823, nom. cons., non Gymnostomum Hedw., 1801, nom. rejic. Lectotype: Gymnostomum calcareum Nees & Hornsch.

Sect. Gymnostomum

Gymnostomum subg. Eugymnostomum Schimp., Syn. 39, 1860, nom. illeg.

Gymnostomum subg. Gymnostomum Kindb., Eur. N. Amer. Bryin. 2: 284, 288, 1897, nom. illeg.

Bryum sect. Gymnostomum (Hedw.) Relh., Fl. Cantabr. ed. 2: 424, 1802.

Gymnostomum sect. Holomitria Wallr., Fl. Crypt. Germ. 1: 94, 1831, p.p.

Trichostomum sect. Pycnocaulus Lindb. ex Milde, Bryol. Siles. 106, 1869.

Sect. Diastoma Griff., Calcutta J. Nat. Hist. 2: 481, 1842.

Habitat:

            Found on rock (usually calcareous, occasionally acid) in very moist areas; widely distributed on most continents.

Notes:

            Gymnostomum might be viewed as a much reduced, hygrophilic segregate of Barbula, an end-member of a phyletic series beginning with Barbula sect. Barbula, and extending through B. sect. Convolutae, Leptobarbula and Gyroweisia. Cladistic analysis (Cladograms 11 and 14), however, does not support more than a close relationship with Barbula. The generally well developed papillae (Pl. 46, f. 9) of Gymnostomum, especially as they roughen the upper laminal margins, are like those of Barbula, but the firm-walled basal cells of the axillary hairs and the costa ending below the apex are more characteristic of Didymodon.

            Large plants of Gymnostomum aeruginosum (e.g. U.S.A., Flowers, Utah, 331, US, and Czechoslovakia, Pilous 857, DUKE) have a tendency toward a leaf base differentiated in shape (becoming rectangular) but the apex of such large plants is more like that of Hymenostylium, the costa being percurrent or vaguely excurrent as a broadly triangular mucro, or percurrent and the apex rounded-acute, as is commonly the case in Didymodon sect. Didymodon, not excurrent and clearly distinct from the tissue of the lamina as is the case with Barbula. Hilpert's (1933) combination Barbula mosis (Lor.) Hilp. shows a sensitivity on his part to the Barbula relationship, as does K. Saito's annotation of a combination in Barbula on the type of G. hymenostylioides (as Merceyopsis) at H, with the comment: “Though the species lacks peristome teeth, it seems to be on the same evolutionary (or reductive) line with Barbula indica. I think it may be more natural to treat it [as] a member of the genus Barbula.”

            Large specimens of Gymnostomum aeruginosum may also have distinctly serrulate lower leaf margins, much as is the case in Molendoa hornschuchiana, a large end-member of a stature gradient extending through M. sendtneriana, and the serrulate perichaetial leaves of some large specimens of G. aeruginosum and those of G. bewsii are quite similar to those of M. sendtneriana. Evidence of apparent phenocopy phenomena (including presence of propagula in small forms of M. sendtneriana) between the two genera at the small end of both of their stature gradients (Zander 1977c, p. 261) supports this relationship. Eucladium, however, also has denticulate lower laminal margins and is not closely related to Gymnostomum or Molendoa, and it is possible that this characteristic is merely typical of hygrophilic species. Although Molendoa when sterile can generally be distinguished from Gymnostomum by the percurrent or excurrent costa and more massive, scab-like laminal papillae, this is not always the case. Additional discussion on the morphological similarities of Gymnostomum and Molendoa has been given by Newton (1983), who favored a more analytic approach to species distinctions. Cladistic analysis gives differing results as to the relationship of Gymnostomum and Molendoa, but see discussion of Cladograms 14–16.

            Within Gymnostomum itself, there is a clear reduction series based on leaf shape (ligulate to ovate) from G. aeruginosum (Pl. 46, f. 3–4) to G. mosis, with elaborations such as propagula in G. virdulum (Pl. 46, f. 19, and rarely in G. aeruginosum), thickened costae in G. hymenostylioides, and bistratose upper laminal margins in G. bewsii (Pl. 46, f. 13—often present in G. aeruginosum from the southeastern U.S.A.). Gymnostomum viridulum (Pl. 46, f. 14–19; cf. Sérgio 1984, also Whitehouse & Crundwell 1991, 1992) is doubtfully different from G. mosis, while G. hymenostylioides is very similar to both taxa in its leaf being widest at the middle but the latter has a longer leaf and very stout costa. Although I have synonymized G. calcareum with G. aeruginosum (Zander 1977c), because these appear to intergrade in the New World, the two are apparently distinct in Europe (see e.g. Whitehouse & Crundwell 1991, 1992) and, for this treatment to be of maximum service, both names are recognized here. Khanna (1976) has pointed out that “G. recurvirostrum [= Hymenostylium recurvirostrum]¼, G. calcareum¼and G. aeruginosum cannot be called clearly marked species because of the presence of intergrading forms among them, at least in the area under investigation [the Himalayas]. However, they are morphologically distinct from each other and statistical distances among them can be defined.”

            Eventually, certain of the names presently accepted as combinations in Gymnostomum will probably be assigned to other genera, such as Hymenostylium or Anoectangium. For instance, G. chenii is surely the same as H. recurvirostrum var. cylindricum, if one may judge from Saito's (1973c) detailed illustrations.

Literature: Andrews (1922b), Brown (1894a), Crum & Anderson (1956), Crundwell (1981), Geheeb (1906a), Khanna (1976), Nyholm and Hedenäs (1986), Pierrot (1973, 1989), Stirling (1968).
Number of accepted species: 24
Species Examined: G. aeruginosum, G. bewsii (PRE), G. calcareum (BUF), G. hymenostylioides (BM, H), G. luisieri (LISU), G. mosis (BUF, MO).

 

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            Plants growing in turf or cushions, light to dark or olive green above, light to dark brown below. Stems branching often, to 2.7 cm in length, transverse section rounded-pentagonal to occasionally rounded-triangular, central strand usually present, weak, sclerodermis absent or occasionally present, hyalodermis present or absent; axillary hairs 3–10 cells in length, the basal 1–2 usually brownish; sparsely radiculose or occasionally red tomentose. Leaves appressed to appressed-incurved when dry, weakly spreading to spreading-recurved when moist, usually ligulate, occasionally ovate to circular, short, to 1.1(–1.8) mm in length, upper lamina flat to broadly convex, occasionally keeled, margins plane or occasionally recurved below midleaf, entire or minutely crenulate by projecting papillae, sometimes bistratose marginally above midleaf; apex rounded obtuse to broadly acute, often apiculate; base scarcely differentiated or seldom ovate-rectangular, sometimes denticulate marginally; costa ending 2–5 cells below apex, only occasionally percurrent, occasionally swollen at or above midleaf, ventrally usually bulging, ventral superficial cells quadrate or short-rectangular, occasionally elongate, dorsally elongate or occasionally short-rectangular to quadrate above midleaf, both sides of costa papillose, 2–4(–6) rows of cells across costa ventrally at midleaf, costal transverse section ovate to semicircular, stereid bands weak or lacking ventrally, present but often weak dorsally, ventral epidermis present, dorsal occasionally little differentiated, guide cells 2(–4) in 1 layer, hydroid strand absent; upper laminal cells subquadrate, 7–11 µm in width, 1:1, walls thin to weakly evenly thickened, seldom irregularly thickened and lumens angular, homogeneous, superficially flat to convex on both sides, often appearing wrinkled in section because of hollow papillae, cells of apex often in rows that “criss-cross” at right angles just below the apex; papillae simple to bifid, low, small, scattered, generally crowded, 3–5 per lumen, hollow or solid; basal cells differentiated across leaf or rising higher medially, rectangular, little wider than upper cells, 2–4:1, walls thin. Propagula occasionally present, spherical to obovoid or spindle-shaped, of 5–10 usually multiseriate cells, borne on branching stalks in leaf axils. Dioicous. Perichaetia terminal, inner leaves ovate-lanceolate, to 1.5 mm in length, sheathing below midleaf, sometimes marginally serrulate, cells rectangular and occasionally bulging below midleaf. Perigonia gemmate, terminal. Seta generally 0.3–0.6 cm in length, 1 per perichaetium, yellowish to reddish brown, twisted clockwise; theca 0.5–0.8 mm in length, yellowish to reddish brown, ovoid to elliptical, occasionally with a weak but high circumstomal ring, exothecial cells quadrate to rectangular, walls thin to somewhat thickened, stomates phaneropore, at base of theca, annulus of 1–3 rows of smaller, transversely elongated, occasionally vesiculose cells; peristome teeth absent. Operculum rostrate to conic-rostrate, ca. 0.4–0.5 mm in length, cells in straight rows. Calyptra cucullate, smooth, 0.5–1.2 mm in length. Spores 9–15 µm in diameter, brownish, essentially smooth to clearly papillose. Laminal KOH color reaction usually yellow to yellow-orange, occasionally red in patches. Reported chromosome number n = 13.

 
 
 
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