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Published In: Bulletin of the Torrey Botanical Club 42: 396, pl. 23. 1915. (Bull. Torrey Bot. Club) Name publication detailView in BotanicusView in Biodiversity Heritage Library

Project Name Data (Last Modified On 1/26/2013)
Acceptance : Accepted
Project Data     (Last Modified On 10/7/2017)
Plant Category: Mosses
General Reference:

Notes     (Last Modified On 10/7/2017)
Pseudocrossidium contains 16 species, rather widely distributed in highland regions; eight species in the Neotropics. Open montane to páramo and puna in the Tropical Andes; associated with rather dry vegetation, on soil or rock. The genus is distinguished, in part, by the poorly developed (sometimes absent) upper stereid band and strongly developed, often crescent shaped lower stereid band with very thick-walled epidermal layer below. Two further notable features present in some but not all species are the development of photosynthetic tissue in the form of filaments on the adaxial surface of the costa, and strongly revolute-rolled leaf margins. The concept of Pseudocrossidium has been modified considerably by Zander (1979, 1981, 1993) from previous workers (e.g., R.S. Williams). It now includes a number of the species previously placed in Barbula. The following keys adapted and modified from Zander (1979).
Pseudocrossidium contiene 16 especies, ampliamente distribuidas; ca. 8 especies en el Neotrópico. El género se distingue, en parte, por las estereidas de la banda superior poco desarrolladas (algunas veces ausentes) y la banda inferior de estereidas marcadamente desarrolladas, a menudo de forma creciente, con una capa de células epidérmicas de paredes muy gruesas por debajo. Dos características muy notorias presentes en algunas, pero no todas las especies, son el desarrollo de tejido fotosintético en forma de filamentos sobre la superficie adaxial de la costa y márgenes de las hojas marcadamente revoluto-enrollados. El concepto de Pseudocrossidium actualmente incluye a varias especies previamente localizadas en Barbula.


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Plants forming loose to dense tufts, dark green to blackish- or brownish-green. Stems erect, 3-20 mm tall, few branched, weakly radiculose; hyalodermis usually absent or weak, central strand present. Leaves erect to spirally-twisted when dry, erect-spreading when wet, oblong-ligulate, ovate or ligulate to lanceolate, 0.5-3.0 mm long, apex obtuse to acute; margins recurved distally and plane below, or strongly spirally-revolute, entire; cost strong, subpercurrent or short excurrent and mucronate or with a short smooth awn, superficial cells quadrate to short rectangular, upper cells papillose, differentiated as a pad of papillose, thin-walled filaments, in cross-section reniform to circular, stereid band strong below, weak or absent above, guide cells 2-4 (rarely more) across, epidermal cells large; laminal cells subquadrate to hexagonal, generally papillose, papillae crowded, bifid to multiplex; basal cells differentiated medially or across, rectangular, thin to rather thick-walled. KOH leaf color reaction yellow to orange, occasionally with red blotches. Gemmae infrequent, when present on upper surface of leaf costa or axils, clavate or spherical. Dioicous. Perichaetia terminal; leaves undifferentiated or more commonly strongly differentiated, often elongate, convolute-sheathing, and awned. Setae elongate, ca. 10-15 mm long, twisted. Capsules erect, urn cylindrical to elliptical, ca. 1.6-3.0 mm long; exothecial cells short rectangular; stomata few at urn base; annulus in 2-4 rows, persistent; operculashort to long conic or short rostrate; peristome single, teeth divided into 32 filaments to base, twisted or occasionally erect, spiculose, basal membrane absent or low. Calyptrae cucullate, smooth and naked. Spores spherical, nearly smooth to lightly papillose.
Plantas pequeñas a medianas, formando manojos laxos hasta densos, verde oscuro hasta negruzcas- o verde-parduzcas. Tallos erectos, ca. 3-20 mm de alto, poco ramificados, débilmente radiculosos; hialodermis generalmente ausente o débil, cordón central presente. Hojas erectas a espiralmente torcidas en seco, erecto-extendidas en húmedo, oblongo-liguladas, ovadas o liguladas hasta lanceoladas, ca. 0.5-3.0 mm de largo, ápices obtusos hasta agudos; márgenes recurvados distalmente y planos abajo, o marcadamente espiralmente-revolutos, enteros; costa fuerte, subpercurrente o corto-excurrente y mucronada o con una arista corta y lisa, células superficiales cuadradas hasta corto-rectangulares, células superiores papilosas o diferenciadas en almohadillas de filamentos papilosos, con paredes celulares delgadas, en corte transversal reniformes hasta circulares, banda inferior de estereidas fuerte, banda superior débil o ausente, 2-4 guía células (raras veces más) transversales, células epidérmicas grandes; células de la lámina subcuadradas hasta hexagonales, generalmente papilosas, papilas agregadas, bífidas hasta múltiples; células basales diferenciadas medial o transverlmente, cuadradas hasta rectangulares, paredes celulares delgadas a bastante gruesas. Yemas poco frecuentes, cuando presentes en la superficie superior de la costa o axilas de las hojas, claviformes o esféricas (yemas no presente en las especies de Bolivia). Dioicas. Periquecios terminales; hojas indiferenciadas o más frecuentemente muy diferenciadas, a menudo alargadas, convolutas-amplectantes y aristadas. Setas alargadas, ca. 10-15 mm de largo, torcidas. Cápsulas erectas, urna cilíndrica hasta elíptica, ca. 1.5-3.0 mm de largo; células exoteciales corto-rectangulares; pocos estomas en la base de la urna; anillo en 2-4 filas, persistente; opérculo corto- hasta largo-cónico o corto-rostrado; peristoma simple, dientes partidos en 32 filamentos hasta la base, torcidos u ocasionalmente erectos, espiculados, membrana basal ausente o baja. Caliptra cuculada, lisa y desnuda. Esporas esféricas, casi lisas hasta finamente papilosas.

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1. Upper (adaxial) epidermal cells of costa in one layer above guide cells, not forming filaments … 2.
1. Upper (adaxial) epidermal cells of costa in 2-several layers above guide cells, usually differentiated as separate filaments … 3.
2. Leaf apices apiculate … P. replicatum
2. Leaf apeices awned … P. arenicolum
3. Leaf margins spiral-revolute, interior cells strongly chlorophyllose, thin-walled, hollow-papillose … 4.
3. Leaf margins not differentiated as photosynthetic organs … 6.
4. Leaves 0.5-0.7 mm long, apiculate … P. excavatum
4. Leaves 1.2-1.8 mm long, mucronate to short-awned … 5.
5. Leaves mucronate (Bolivia) … P. pachygastrellum
5. Leaves short-awned (Peru to Chile) … P. apiculatum
6. Leaf margins distally enfolded; propagula present in leaf axil … P. granulosum = Andina
6. Leaf margins plane or recurved; propagula absent … 7
7. Leaves acute-apiculate, costa percurrent; perichaetial leaves weakly differentiated … P. elatum = Andina
7. Leaves obtuse, costa ending below the apex; perichaetial leaves strongly differentiated … P. chilense
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