Pleuridium Rabenhorst, Deutschl. Krypt. Fl. 2(3): 79. 1848.
[conserved name]
[Greek, pleuridion, the sporophytes often emerge laterally from the perichaetium]
Kwok Leung Yip
Plants ephemeral or annual, gregarious to loosely tufted, 3--7 mm, yellow-green. Stems simple or innovating, in transverse section with epidermis, cortex, and a well-developed central strand; rhizoids basal on stem, brown, smooth; axillary hairs smooth. Stem leaves erect-spreading or appressed, concave, imbricate to spreading; proximal leaves linear to deltoid, percurrent, cells oblong. Distal and perichaetial leaves oblong to lanceolate with subulate to acuminate tips, margins plane and undifferentiated, entire to serrate or abruptly toothed, marginal cells slightly longer than adjacent lamina cells; basal cells quadrate-rectangular; median cells irregular, rhomboidal to trapezoidal; distal cells elongated; alar cells not differentiated; costa single, subpercurrent to excurrent, smooth to roughened on the abaxial surface, stereid bands one or two, guide cells centrally located, confluent with the cells of the leaf lamina. Specialized asexual reproduction by innovations (and reportedly by rhizoidal tubers). Sexual condition monoicous. Perigonia occur proximal to perichaetium with antheridia generally naked in leaf axils (paroicous), or in small buds in axils of stem leaves (autoicous); paraphyses present, antheridia spindle-shaped with short delicate stalks, (1--)2(--5) per perigonia. Perichaetia single, terminal on mature stem, with 3--8 perichaetial leaves similar to the distal cauline leaves, paraphyses smooth, archegonia 3--5. Vaginula cylindrical to flask-shaped. Sporophytes 1(--2) per perichaetium. Seta short, straight or curved, smooth. Capsule cleistocarpous, erect on the seta, immersed, orange to brownish, ovoid to elliptical, smooth, no distinct neck, columella cylindrical, stomata 4--10, superficial (phaneroporic), restricted to base of capsules, annulus none, operculum none, rostrum erect, apex sharp to acuminate, peristome none. Calyptra mostly persistent, cucullate, smooth, with entire rim. Spores spherical, non-polar, 15--38 µm, papillose to short-spinose, yellowish to orange.
Species 21 (4 in the flora): worldwide except Antarctica; moist, exposed soil in open, disturbed and weedy habitats, old-fields and roadside ditches, as pioneers in the first year after initial disturbance.
Pleuridium is related to Ditrichum, a stegocarpous genus also in the Ditrichaceae, because of a demonstrated hybridization relationship (L. E. Anderson 1980) and by similarities in gametophyte morphology and molecular characters (C. LaFarge et al. 2000). Pleuridium is also closely related to Cleistocarpidium by the immersed cleistocarpous capsules but Cleistocarpidium palustre has mitrate calyptras and pale whitish capsules, which are asymmetrical and stomatose to the equator. In Pleuridium, sporophytes may emerge laterally from the perichaetium, not because of an actual lateral origin or position, but owing to the curvature of a short seta (H. Crum A. and L. E. Anderson 1981), or because a new innovation originated proximally and developed beyond the perichaetium (P. C. Chen et al. 1963), in some species of Archidium originally included in the genus (S. E. Bridel 1819; J. A. Snider and W. D. Margadant 1973). Rhizoidal tubers were reported for the genus by T. Arts and S. Risse (1988). The "central accessory cells" as used here are equivalent to Begleiter or hydroid cells of other others.
SELECTED REFERENCES
Anderson, L. E. 1980. Ctyology and reproductive biology of mosses. In: R. J. Taylor and A. E. Leviton, eds., The mosses of North America: an inquiry into the biology of mosses based on a symposium. San Francisco: Pacific Division of AAAS. Pp. 37--76. Arts, T. & S. Risse. 1988. The occurrence of rhizoidal tubers in Pleuridium acuminatum. Lindbergia 14: 127--130. Britton, E. G. 1913. Ditrichaceae. North American Flora 15(1): 55--66. Bruch, P. & W. P. Schimper. 1835. Comparaison entre les Phascum alternifolium, Phascum palustre et Phascum subulatum. Mémoires de la Société du Muséum D'histoire Naturelle de Strasbourg 2: 1--4. Bryan, V. S. 1956. Chromosomes and systematic position of the inoperculate mosses, Pleuridium and Bruchia. Amer. J. Bot. 43: 460--468. Chen, P. C., T. L. Wan, C. Gao, X. J. Li & P. C. Wu (eds.). 1963. Genera muscorum sinicorum, pars prima. Beijing: Science Press. [In Chinese] Crum, H. A. & L. E. Anderson. 1981. Mosses of Eastern North America, Vol. 1. New York. Grout, A. J. 1936. Moss Flora of North America North of Mexico, Vol. 1. Newfane, Vermont. La Farge, C., B. D. Mishler, J. A. Wheeler, D. P. Wall, K. Johannes, S. Schaffer and A. J. Shaw. 2000. Phylogenetic relationships within the haplolepideous mosses. Bryologist 103: 257--276. Snider, J. A. and W. D. Margadant. 1973. Proposal for the conservation of the generic name Pleuridium Rabenh. (1848) against Pleuridium Brid. (1819) (Musci). Taxon 22: 691--694. Yip, Kwok Leung. 2000. A Revision of the Genus Pleuridium (Musci, Ditrichaceae). Ph.D. Dissertation, University of Cincinnati, Cincinnati. Yip, Kwok Leung. 2002. Lectotypification of Pleuridium subulatum and P. acuminatum. Bryologist 105: 259--261.
OTHER REFERENCES
Anderson, L. E., H. A. Crum and W. R. Buck. 1990. List of the mosses of North America north of Mexico. Bryologist 93: 448--499.
Austin, C. F. 1877. New mosses. Bull. Torrey Bot. Club 6: 142--145.
Bridel, S. E. 1819. Methodus nova muscorum: ad naturae mormam melius instituta et muscologiae recentiorum accommodata, Muscologiae recentiorum supplement, pars IV, seu Mantissa Generum Specierumque Muscorum Frondosorum Universa. Gotha.
Crum, H. A., W. C. Steere and L. E. Anderson. 1973. A new list of mosses of North America north of Mexico. Bryologist 76: 85--130.
Lawton, E. 1971. Moss Flora of the Pacific Northwest. Nichinan.
Lesquereux, L. and T. P. James. 1884. Manual of the Mosses of North America. Boston.
Lindberg, S. O. 1863. Bidrag till mossornas synonymi. Öfversigt af Förhandlingar: Kongl. Svenska Vetenskaps-Akademien 20: 385--418.
Lindberg, S. O. 1865. Om bladmossornas locklösa former. Öfversigt af Förhandlingar: Kongl. Svenska Vetenskaps-Akademien 21: 575--588.
Matsui, T. and Z. Iwatsuki. 1990. A taxonomic revision of the family Ditrichaceae (Musci) of Japan, Korea and Taiwan. J. Hattori Bot. Lab. 68: 317--366.
Smith, A. J. E. and M. E. Newton. 1968. Chromosome studies on some British and Irish mosses. III. Trans. British Bryol. Soc. 5: 463--522.
Snider, J. A. 1994. Pleuridium Rabh., nom. cons. In: A. J. Sharp, H. Crum and P. M. Eckel (eds.), The Moss Flora of Mexico. Pp. 92-98. Bronx.
Steere, W. C., L. E. Anderson and V. S. Bryan. 1954. Chromosome studies on California mosses. Mem. Torrey Bot. Club 20(4): 1--75.
Watson, S. 1880. Botany [of California]. Vol. 2. Cambridge, Mass.
Xu, P.-S. 1989. Cryptogamic flora of the Yangtze Delta and adjacent regions. Shanghai. [In Chinese]
