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BFNA | Family List | BFNA Vol. 1 | Polytrichaceae

Atrichum Palisot de Beauvois, Mag. Encycl. 5: 329. 1804.
[conserved name]

[Greek a-, without and trichos, hair, referring to the hairless calyptra]

Gary L. Smith Merrill and Robert R. Ireland

  • Catharinea F. Weber & D. Mohr [rejected name]

    Plants small to robust, not polytrichoid, in loose tufts. Stems simple or rarely sparingly branched. Leaves without a differentiated sheath, membranous, strongly crisped and contorted when dry, widely spreading and plane to ± distinctly concave when moist, with a differentiated border of 1 or more rows of narrow, linear, thick-walled cells, the border usually 2-stratose, the margins toothed to mid-leaf or below with single or paired teeth (teeth and cells of leaf border papillose in A. crispum); costa narrow, abaxially toothed in distal half or rarely smooth, bearing adaxial lamellae; abaxial lamellae none; lamina 1-stratose except for margins, often obliquely transversely undulate and abaxially toothed along the undulations, or almost plane and not abaxially toothed; lamellae ± straight or tall with sinuous margins, rarely rudimentary and almost lacking, entire in profile, the marginal cells in section not differentiated, smooth; basal cells of lamina short- to long-rectangular, in longitudinal rows; median cells subquadrate to transversely elongate-hexagonal, in ± regular longitudinal rows, thin- to firm-walled, with or without distinct trigones, slightly convex on both surfaces (adaxial surface bulging-mammillose in A. angustatum), smooth or with minute rounded to striate papillae. Sexual condition dioicous, polygamous, or synoicous; perigonia inconspicuous, the bracts resembling the leaves, or the bracts broadly ovate and overlapping, forming a conspicuous disc, sometimes with more than one male inflorescence in sequence per plant; perichaetial leaves usually narrower and longer than the stem leaves. Seta 1(--3) per perichaetium, straight to flexuose, twisted near the capsule when dry, smooth. Capsule short- to long-cylindric, ± straight to arcuate, terete, finely striate when dry, lacking a basal constriction; stomata none; exothecium smooth, the cells elongate-rectangular, not pitted, the longitudinal walls thickened; operculum rostrate, the beak straight to arcuate; peristome teeth 32, simple, linear and crowded. Calyptra cucullate, smooth or merely hispid at tip. Spores finely papillose, appearing smooth.

    Species ca. 20 (9 in the flora). North America, West Indies, Central America, South America, Europe, Asia, Africa, Australia.

    Atrichum is unique in the family in having distinctly bordered, transversely undulate leaves. The peristome, however, is almost identical to that of Psilopilum, suggesting a close relationship. Inflorescence types are important differences between species, but are sometimes difficult to demonstrate. Dioicous (presumably heterothallic) species have antheridia and archegonia on separate male and female plants (A. angustatum, A. crispulum, A. crispum, A. selwynii, A. tenellum). Polygamous (heteroicous) species have both unisexual and bisexual shoots, the latter protandrous, with a male inflorescence followed by a female after an interval of vegetative growth (A. altecristatum, A. cylindricum, A. undulatum). Atrichum flavisetum is synoicous, with antheridia and archegonia within the same involucre, the perigonia hidden among the perichaetial leaves.

    T. C. Frye's treatment of Atrichum in Grout's Moss Flora (T. C. Frye 1937) emphasizes the fractions of leaf width obscured by the lamellae, without taking into account many useful characters and important distributional differences. Frye's treatment of distinctive North American taxa as varieties of A. undulatum has also delayed recognition of unique aspects of our flora. Three species of the flora are endemic to eastern North America (A. altecristatum, A. crispum, A. cylindricum), and 1 to the West (A. selwynii). Atrichum crispulum is disjunctive in eastern North America and eastern Asia, whereas true A. undulatum appears to be an introduced species in North America.


    Frye, T. C. 1910. The Polytrichaceae of western North America. Proc. Washington Acad. Sci. 12: 275--281. Frye, T. C. 1937. Atrichum. In: A. J. Grout, Moss Flora of North America North of Mexico. 1: 100--106. Newfane. Ireland, R. R. 1969. Taxonomic studies on the genus Atrichum in North America. Canad. J. Bot. 47: 353--368. Ireland, R.R. 1971. Atrichum. In: E. Lawton, Moss Flora of the Pacific Northwest. Nichinan. Pp. 31--33, pl. 5. Ireland, R. R. 1982. Moss Flora of the Maritime Provinces. Publications in Botany 13, National Museums of Canada. Ottawa. Pp. 665--674. Ireland, R. R. 1993. Scanning microscope study of spores of the genus Atrichum (Musci: Polytrichaceae). J. Hattori Bot. Lab. 74: 205--217. Nyholm, E. 1971. Studies in the genus Atrichum P. Beauv. A short survey of the genus and species. Lindbergia 1: 1--33.


    Ireland, R. R. 1991. Cuticular papillae of Atrichum crispum. Bryologist 94: 73--76.
    Jennings, O. E. 1951. A Manual of the Mosses of Western Pennsylvania and Adjacent Regions, ed. 2. Amer. Midl. Naturalist Monogr. 6.
    Smith, G. L. 1977. Atrichum cylindricum (Polytrichaceae), an overlooked moss in the southeastern United States. Brittonia 29: 368--375.
    Steere, W. C., L. E. Anderson and V. S. Bryan. 1954. Chromosome studies on California mosses. Mem. Torrey Bot. Club 20: 1--27.
    Warnstorf, C. 1914. Zur Bryo-Geographie des Russischen Reiches. Hedwigia 54: 22--182.

    Alternative Key

    1 Plants monoicous, at least some shoots bearing both antheridia and archegonia.   (2)
    + Plants dioicous, plants bearing either antheridia or archegonia, but not both.   (5)
    2 (1) Plants synoicous; setae appearing lateral due to continued growth of stem .   Atrichum flavisetum
    + Plants polygamous; setae terminal.   (3)
    3 (2) Leaves narrowly lanceolate to linear, subfalcate, not or scarcely undulate, with few or no abaxial teeth; lamellae low and strictly parallel. Atlantic and Gulf coastal plain, Mississippi embayment.   Atrichum cylindricum
    + Leaves ovate-lanceolate to elliptic-lanceolate, usually undulate with abaxial teeth; lamellae taller and laxly spreading.   (4)
    4 (3) Capsules straight and suberect; leaves often rather narrow; common, ne and nc U.S. and Canada.   Atrichum altecristatum
    + Capsules arcuate, horizontal; leaves elliptic-lanceolate; rare, e Canada, B.C.   Atrichum undulatum
    5 (1) Median leaf cells 30 µm wide or more.   (6)
    + Median leaf cells (8--)15--25(--30) µm wide.   (7)
    6 (5) Leaf margins regularly toothed, teeth striate-papillose; leaves not undulate, with few or no abaxial teeth; median leaf cells 35--52 µm wide, thin-walled, lacking trigones, e North America.   Atrichum crispum
    + Leaf margins coarsely toothed, the teeth crowded near apex, smooth; leaves undulate, often with oblique rows of abaxial teeth; median leaf cells 27--40(--48) µm wide, firm-walled, with small distinct trigones; w North America.   Atrichum selwynii
    7 (5) Median leaf cells 8--17 µm wide, ± isodiametric, bulging-mammillose on the adaxial leaf surface; lamellae 6--9, to 10(--15) cells high.   Atrichum angustatum
    + Median leaf cells 19--27(--30) µm wide, laxly subquadrate to transversely elongate hexagonal, convex on both surfaces; lamellae 2--6, to 6 cells high.   (8)
    8 (7) Leaf cells 19--24 µm wide, laxly subquadrate; lamellae 2--5, 4--7 cells high; small plants, to 2 cm.   Atrichum tenellum
    + Leaf cells 24--27(--30) µm wide, transversely elongate hexagonal; lamellae 4--6, up to 2--4(--6) cells high; large plants, to 6 cm.   Atrichum crispulum

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