Tropicos | Name - !Pseudocrossidium R.S. Williams

Cent. Amer. Moss > Pottiaceae > Pseudocrossidium

Choose Project down

English

!Pseudocrossidium R.S. Williams

Search in Index Nominum Genericorum (ING)

Search in African Plants Database at Geneva Botanical Garden

African Plants, Senckenberg Photo Gallery

Project Name Data (Last Modified On 2/16/2011)

Acceptance : Accepted

Project data (Last Modified On 2/16/2011)

Discussion:

Pseudocrossidium was established by Williams (1915) for a group of dioicous species with a distinct stem central strand, revolute leaf margins in which the interior cells were thin-walled or had greatly enlarged papillae, 1 or 2 costal stereid bands, superficial ventral costal cells greatly elaborated (sometimes as filaments), and strongly differentiated perichaetial leaves. Zander (1993) enlarged the concept of the genus to include species that lacked strongly differentiated marginal cells. He distinguished Crossidium from Pseudocrossidium on the basis of its oval rather then reniform costa, undifferentiated upper leaf margins, single (dorsal) costal stereid band, and weakly bulging upper median leaf cells, but none of these features consistently distinguishes the two genera.

There are species of Barbula and Bryoerythrophyllum similar to Pseudocrossidium in leaf shape, and in having revolute margins. Both genera differ from Pseudocrossidium in having two costal stereid bands, and less broadly, tightly revolute leaf margins that lack strongly differentiated interior cells.

Keys to the species of Pseudocrossidium are given by Eckel et al. (1997) for North America and Zander (1979) for South America.

Export To PDF

Export To Word

Pseudocrossidium Williams, Bull. Torrey Bot. Club 2: 396. 1915.

Barbula sect. Pseudocrossidium (Williams) Nyholm, Ill. Fl. Nord. Mosses 2: 102. 1989 [1990].

Barbula sect. Revolutae Bruch & Schimp. in B.S.G., Bryol. Eur. 2: 89. (Fasc. 13–15: 27). 1842. Tortula sect. Revolutae (Bruch & Schimp.) Spruce, Ann. Mag. Nat. Hist. ser. 2, 3: 377. 1849. Barbula subsect. Revolutae (Bruch & Schimp.) Chen, Hedwigia 80: 209. 1941.

Plants small to medium-sized, green or yellow-green above, reddish brown below, in tufts. Stems red, not or sparsely branched, sclerodermis or hyalodermis present, central strand exceptionally well-developed; rhizoids sparse. Axillary hairs 5–6 cells long, all cells hyaline. Leaves elliptic, oblong or obovate-lanceolate, erect or spreading at base, spirally appressed when dry, erect-spreading to spreading-recurved when wet, lamina unistratose; apices broadly acute to obtuse-rounded, mucronate; margins spirally revolute to the apex, the interior cells of the revolute margins, thin-walled, weakly papillose, hyaline or green; costa stoutly excurrent as a smooth mucro, guide cells and a single (dorsal) stereid band present, ventral surface layer enlarged, thin-walled, papillose; upper cells in regular rows, subquadrate, hexagonal or oblate, firm-walled, densely papillose, basal cells quadrate, subquadrate, rectangular, or long-rectangular, firm-walled, smooth, at times inner basal cells yellow-orange, alar cells not differentiated. Dioicous. Perichaetia and perigonia terminal. Setae smooth. Capsules cylindrical, erect; exothecial cells short-rectangular; stomata in neck; opercula slightly inclined, long-rostrate; annuli of 2–3 layers of small, non-vesiculose cells; peristome yellow-orange, basal membrane high, teeth long, spirally twisted, densely spiculose. Spores smooth or lightly roughened. Calyptrae cucullate.