Flora of North America, Volume 27, 2007

506 POTTIACEAE · Tortella Variety arctica is easily distinguished by the leaf cells keeled in section, costa in apical region exposed adaxially extremely thick-walled and obscured by massive papillae, by up to two stereid cells in width or completely covered and the proximal cells grading gradually into the distal with an adaxial epidermis of quadrate papillose cells; leaf laminal cells. However, intermediates in anatomical cross section with 2-stratose areas beside the costa, the characters are abundant in more temperate situations in lamina irregularly 2-stratose in patches, lamina tattered, a zone between north boreal regions and the Arctic costa occasionally appearing undifferentiated in apical (extreme north). Intermediate specimens are also found region of the leaf, adaxial stereid layer occasionally at higher elevations in the south Boreal zone and in wet disappearing toward the apex, epidermal layer may be continental (coastal) margins in the extreme northern continuous throughout the leaf length. Arctic and Greenland. The most distinctive representative Soapstone quarry, limestone pavement; moderate specimens are a blackened brick-red, with very long stems, elevations; low to high elevations; Alta., B.C., Que.; and so densely foliose with rigid leaves as to appear to Alaska, Calif., Mich., N.Y., Vt., Wash.; Europe. felt the substrate on which they grow with woolly mats. Variety fragilifolia is characterized by extremely fragile However, in sites that have more temperate conditions, leaf apices that may be all absent, leaf cross-section especially at the southern limit of its range, the species irregularities (2-stratose areas juxtacostally), relatively varies such that the stems may be less foliose, hence less broad leaves that are rather shortly mucronate with dense except in innovating whorls and at the apex, the quadrate cells on the adaxial surface of the costa dry leaves become more contorted at the stem apex, the extending to the leaf apex. The adaxial stereid band red color subsides toward the yellow-green of Tortella disappears distally, but the adaxial epidermal layer tortuosa, the sclerodermis recedes to resemble that of the remains intact, an unusual characteristic for species of typical variety and the distal laminal cells have thinner the genus. Although the stem in section appears rather walls, tiny papillae and are strikingly set off from the larger than is typical for the var. tortuosa, a distinctive proximal cells which are thin and lax, clear and free of central strand is rarely present. The stems usually have a papillae. Such plants then have more tortuous leaves dense rufous tomentum. The leaves differ by being little when dry. In such specimens, one must rely for or not undulate or crisped when dry, but may be undulate identification on the relatively denser habit, at least at when wet; they are usually only once circinate and the stem apex, the leaf shape, with its broader leaf base without the delicate appearance of the typical variety. and more abruptly contracted, more rigid distal lamina, The leaves, within the range of variation of the species, the tubular or canaliculate leaf cross section (not keeled) tend to be somewhat shorter and broadly lanceolate in and the tomentum hidden in the bases of the leaves (rather the proximal two-thirds (not setaceous), and the laminae than exposed). Although T. tortuosa var. arctica may can seem to deteriorate and appear fragile; yet they may replace var. tortuosa in the high Arctic, the former does also be extremely long and narrow (setaceous), especially range to the south into Maine and Colorado. In latitudes in western North American populations. The variety is where the two varieties overlap, distinction becomes easily confused with Tortella fragilis, having a setaceous, highly problematical. The sclerodermis of var. arctica deciduous (but nonpropaguloid) apex. While some leaves can be a thick rind around the central cylinder. have the typical long, glossy mucro of var. tortuosa, in others the mucro is just a small tip surmounting what 4c. Tortella tortuosa var. fragilifolia (Juratzska) appears to be a prolongation of the leaf apex into a Limpricht, Laubm. Deutschl. 1: 605. 1888 canaliculate extension, this frequently broken. Barbula tortuosa var. fragilifolia Infrequently some apices have a solid and circular form Juratzska, Laubm.-Fl. Oesterr.- which, like a finger, together with a vague border of cells 5 Ung., 123. 1882 free of papillae, show a striking affinity with T. fragilis. That the abaxial surface of the costa in the apical portion Plants green or yellow-green, 5 5 of the leaf is often roughened with low papillae is also 5 5 appearing brown proximally, 5 indicative of the propaguloid modifications of T. fragilis, 5 5 5 loosely foliose, some leaf bases as is the tendency toward undifferentiated cells in the exposed, only slightly comose at costa in the apical region. The laminal cells in the distal stem apex. Stems conspicuously half of the leaf can become very small and obscure: 5–7 tomentose. Leaves in loose, simple µm on average with transversely flattened marginal cells. spirals or once circinate when dry, appearing firm or rigid, The laminal cells may also be very large, reaching 17 often fragile and erose, leaf tips often absent; µm. The leaf cross section also frequently resembles a inconspicuously undulate, especially when dry, fragile or smaller celled version of Tortella rigens: small marginal not, erect- to erect-spreading when wet; undulate or plane; cells grading into larger ones beside the costa, there being proximal laminal cells thin-walled and hyaline, sharply a bi-to multi-stratose area juxtacostally. This variety has differentiated in shape and size from the papillose distal been confused with the excluded European species cells, which are papillose in the area of contact; leaves Tortella nitida; see discussion thereunder for differences. Tortella · POTTIACEAE 507 TORTELLA 5. Tortella fragilis (Hooker & Wilson) Limpricht, channeled to subnaviculate, not cucullate, those of Laubm. Deutschl. 1: 606. 1888 modified leaves long-subulate, fragile, the subula obtusely Didymodon fragilis Hooker & thickened and multi-stratose distally and often broken off, youngest leaves arising from the stem apex fully 5 Wilson in T. Drummond, Musc. 5 Amer., 127. 1828 (as fragile) propagulose and subulate; costa short-excurrent as a 5 5 5 smooth or weakly denticulate mucro of 1–5 rhomboidal Plants coarse, rigid, dark green to 5 5 5 cells, in propaguloid leaves, internal cells in section 5 5 5 5 5 yellowish or blackish brown, 5 5 5 5 5 appearing undifferentiated in the subula; adaxial surface 5 5 5 5 5 5 5 elongate. Stems (0.5–)1–5 cm, 5 5 covered by quadrate to short-rectangular, papillose 5 leaves distantly disposed along the laminal cells throughout the leaf except in the stem with shining leaf bases propaguloid leaf portion where a narrow medial groove usually apparent, central strand is covered by elongate (8:1) smooth cells; cross section absent, densely and visibly radiculose the entire stem lunate and broad, adaxial epidermal cells may be length, rarely somewhat tomentose when very small. interrupted in the center, exposing the adaxial stereid layer Stem leaves firm, coarse, rigid, uniform in size and shape by about two cells in width, in propaguloid leaves stereid along the stem and apex, lowermost leaves mostly layers appear undifferentiated in the subula; proximal without leaf tips, leaves typically fragile only at base of laminal cells rather abruptly differentiated from distal deciduous apical subula, stiffly erect-appressed, incurved cells, yellow-hyaline, elongate, firm to laxly thin-walled, (or stem-apical leaves somewhat twisted around the stem smooth; margin with a narrow line of firm- to thin-walled when dry); erect and weakly spreading when moist, cells extending a short way up the lamina or to mid-leaf; narrowly lanceolate to linear, narrowing gradually into distal laminal cells frequently 2-stratose on one or both the distal region until contracting into a narrower laminae beside the costa, or equally extending toward 1 propaguloid region up to /2 the distal leaf length; broadly the margins in various degrees, and becoming completely to narrowly concave, keeled toward the apex in 2-stratose and ultimately undifferentiated in the, nonpropaguloid leaves, 4–6 mm; base broadly oblong; deciduous leaf tips, rounded-quadrate or hexagonal, margins plane to erect, not to somewhat undulate; apex (9–)10–12(–13) µm wide, strongly papillose, areolation narrowly acute, those of nonmodified leaves shallowly more or less distinct; marginal cells in median leaf region 508 POTTIACEAE · Tortella undifferentiated, papillose-crenulate, along the distal 6. Tortella inclinata (R. Hedwig) Limpricht, Laubm. median margin and into the subula differentiated as one Deutschl. 1: 602. 1888 or two rows of smooth, thick-walled, short-rectangular, Tortula inclinata R. Hedwig in F. (4–3:1), epapillose, yellowish cells leading into the Weber and D. M. H. Mohr, Beitr. subulate region and extending to the apex distinctly 5 Naturk., 1: 123, fig. 5. 1806; 5 visible in at least some leaves, sometimes present only in 5 Barbula inclinata (R. Hedwig) 5 young leaves on mature stems. Specialized asexual 5 5 Schwägrichen 5 5 reproduction by deciduous, subulate, rigid, smooth-sided, 5 5 5 5 5 distally thickened apices of all leaves. Sexual condition 5 Plants dull yellow-green to dioicous; perigonia not seen; perichaetial leaves setaceous, yellowish brown distally, brown fragile, with propaguloid modifications as in stem leaves. proximally, elongate, not rosulate. Seta 1.5–2 cm, occasionally two per perichaetium. Stems 0.5–1(–1.5) cm, central Capsule 1.8–3 mm; annulus none or of 1–2 rows of strand absent; stem sparsely rufous radiculose-tomentose weakly vesiculose cells, operculum ca. 1.5 mm; peristome at the base, essentially without tomentum distally. Stem teeth long, spirally wound, twisted 1–3 times. leaves somewhat soft or lax, loosely to more closely Seldom fruiting, capsules mature summer (Jun).

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