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.
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.
Found
on rock (usually calcareous, occasionally acid) in very moist areas; widely
distributed on most continents.
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.
Additional
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).
New
combination: Gymnostomum hymenostylioides (Broth. & Dix.) Zand., comb.
nov. (Merceyopsis hymenostylioides Broth. & Dix., J. Bot. 48:
302, 1910).