Schistidium
Bryol. Europ. 3: 93. 1845,.
Plants (3–)10–40(–180) mm, in dense cushions to loose mats, olivaceous, green, brown, or black, often with yellow, orange, or red tones. Leaves ovate-lanceolate, occasionally ovate-triangular, less commonly lanceolate to linear-lanceolate or elliptical to ligulate, keeled or concave proximally, sharply keeled or nearly flat distally, margins recurved, rarely plane or incurved, distal lamina usually 1-stratose or 2-stratose in striae or patches, rarely 2-stratose, specialized laminal and marginal chlorophyllose structures absent, muticous to long-awned, sometimes ending in a fleshy, multistratose apiculus; basal cells rectangular, with straight or sinuose and thin to thick cell walls; mid leaf and distal cells quadrate, rectangular, or ovate, rarely subtriangular, smooth or papillose, usually sinuose and thick-walled. Gemmae absent. Sexual condition autoicous, rarely dioicous; perichaetial leaves usually enlarged. Seta short, straight. Capsule erect, immersed, symmetric, cylindric or campanulate; annulus rudimentary or absent; operculum rostrate or rarely mamillate, usually falling attached to columella (except S. trichodon). Calyptra cucullate or mitrate, not erose, not fully covering operculum, smooth.
Distribution
North America, Mexico, Central America, South America, Eurasia, Africa, Atlantic Islands, Pacific Islands, Australia, Antarctica.
Discussion
Species ca. 120 (30 in the flora).
The genus Schistidium has consistently fascinated yet confounded bryologists across North America. Treatments vary from region to region, and names applied to specimens at both the species and varietal levels have been as inconsistent as the characters used to differentiate the taxa. The treatment of the S. apocarpum complex by H. H. Blom (1996) and a survey of Nordic species of Schistidium (Blom 1998) assist in a better understanding of the taxonomy of this complex genus in North America, but many problems of taxonomic interpretation remain. Although Schistidium offers a great number of both gametophytic and sporophytic characters for study, some traits are not well understood and further detailed field and laboratory research is needed.
This treatment follows H. Deguchi (1979) and H. H. Blom (1996, 1998), with reservations. For example, North American specimens identified as Schistidium recurvum H. H. Blom seem to differ from the type in significant character states (Blom, pers. comm.), so this species has been omitted. Schistidium lancifolium H. H. Blom and S. umbrosum (J. E. Zetterstedt) H. H. Blom have been included within S. apocarpum. Although S. ambiguum Sullivant has been reported from North America and may be present, all of the North American collections named S. ambiguum that were examined have proved to be another species.
When examining a specimen of Schistidium certain steps are helpful. It is important to examine the leaves proximal to the perichaetial region. Transverse-sections from the distal region to mid leaf of multiple leaves are also critical in most cases. The necessity of numerous transverse-sections is apparent when studying S. papillosum or S. boreale, for example, as some leaves can be slightly papillose and unless numerous sections are made the papillae may be missed. Mature, empty capsules that are not overly degraded, although not always available, should be used. Transverse-sections of the capsules assist in the easier examination of the exothecial cells and peristome teeth. It is also useful to examine more than one capsule if available, as there can be some variation in exothecial cell makeup. As H. H. Blom (1996) pointed out, mixed populations are present in some sites, especially in more humid areas, so care must be taken to ensure that all species in a collection are separated. Blom also provided a great amount of supplementary detail about many of the species treated here.
Selected References
Lower Taxa
Key
| 1 | Leaf costa with one to two well-developed stereid bands; restricted to coastal areas, often within or near the spray zone. | Schistidium maritimum |
| 1 | Leaf costa stereid bands absent; sometimes found in coastal areas, but rarely within or near the spray zone | > 2 |
| 2 | Plants usually in extensive open tufts or mats over soil, litter, and amongst plant bases in arctic fens and tundra, often along drainage channels. | Schistidium holmenianum |
| 2 | Plants usually on rock | > 3 |
| 3 | Costa excurrent as a fleshy, multistratose apiculus, rarely tipped with a tiny denticulate awn | > 4 |
| 3 | Costa sub-percurrent or excurrent as an awn, never as a fleshy, multistratose apiculus | > 6 |
| 4 | Leaves ovate-lanceolate, mostly erect or erect-incurved when dry, keeled throughout; fleshy apiculus short and indistinct; dioicous, sporophytes rare. | Schistidium crassithecium |
| 4 | Leaves linear-lanceolate to ovate-lanceolate, usually curved to falcate, or falcate-secund when dry, weakly keeled distally or concave throughout; fleshy apiculus prominent on most leaves; autoicous, sporophytes common | > 5 |
| 5 | Lamina mostly 2-stratose distally, with 2-stratose strips extending to the leaf base adjacent to the costa. | Schistidium cinclidodonteum |
| 5 | Lamina mostly 1-stratose. | Schistidium occidentale |
| 6 | Dioicous, sporophytes rare; leaves erect and usually imbricate when dry; distal lamina evenly to irregularly 2-stratose; long awns present on most leaves; plants usually fragile, with individual stems easily separated | > 7 |
| 6 | Autoicous, sporophytes usually present; leaves often curved and somewhat spreading, occasionally imbricate when dry; distal lamina 1- or 2-stratose; awns present or absent; plants not fragile | > 8 |
| 7 | Leaves usually ovate-lanceolate, mostly greater than 1.5 mm; distal lamina evenly 2-stratose; margins plane to incurved, awns usually straight. | Schistidium heterophyllum |
| 7 | Leaves usually ovate-triangular, mostly less than 1.5 mm; distal lamina unevenly 2-stratose; margins recurved; awns usually flexuose. | Schistidium tenerum |
| 8 | Distal laminal cells papillose, mainly on abaxial surface | > 9 |
| 8 | Distal laminal cells smooth (note: distal abaxial costal cells and leaf margins near awn sometimes papillose) | > 12 |
| 9 | Awns coarsely spinulose, often strongly decurrent; laminal cells usually strongly papillose with tall, thick papillae often on both abaxial and adaxial surfaces; Arctic species | Schistidium frisvollianum |
| 9 | Awns finely and distantly spinulose or nearly smooth, weakly decurrent or non-decurrent; laminal cells weakly papillose with short papillae mainly on abaxial surface; widespread or more southern species | > 10 |
| 10 | Plants usually red-brown (rusty), rarely black or olivaceous; leaves ± imbricate proximal to the stem apex when dry; capsule usually cupulate. | Schistidium strictum |
| 10 | Plants olivaceous, sometimes partially reddish brown or dull black; leaves not imbricate proximal to the apex when dry; capsule usually cylindric | > 11 |
| 11 | Plants usually dull black, usually purplish when wet; leaf cells with reddish or orange walls; capsule narrowed towards the mouth. | Schistidium boreale |
| 11 | Plants usually olivaceous, sometimes with reddish tones, rarely nearly black, not purplish when wet; leaf cells with hyaline walls; capsule rarely contracted towards the mouth. | Schistidium papillosum |
| 12 | Plants usually along water courses and lakes, often submerged or in splash zones, sometimes along seasonally irrigated ledges or cliffs; costa usually sub-percurrent or percurrent, sometimes excurrent as a hyaline cell, awns rare; capsule often campanulate; spores large, usually greater than 15 µm | > 13 |
| 12 | Plants usually in drier habitats; costa percurrent or excurrent as an awn; capsule cylindric or cupulate, rarely campanulate; spores small, usually less than 15 µm | > 15 |
| 13 | Leaves linear-lanceolate to ligulate, usually nearly flat distally; margins plane or weakly recurved, usually 1-stratose, smooth or weakly crenulate at apex. | Schistidium agassizii |
| 13 | Leaves ovate-lanceolate to ovate-triangular, keeled distally; margins recurved to revolute, usually 2-stratose, denticulate or smooth distally | > 14 |
| 14 | Capsule often campanulate, never narrowed towards the mouth; stems often greater than 5 mm; leaves 1.2-3.2 mm. | Schistidium rivulare |
| 14 | Capsule short-cylindric or ovoid, never campanulate, usually slightly narrowed towards the mouth; stems rarely greater than 2 mm; leaves 1.2-2.2 mm. | Schistidium subjulaceum |
| 15 | Leaves ovate-ligulate to ovate-lanceolate, often with rounded apices, mostly less than 0.7 mm; awns usually absent; capsule short, usually less than 0.6 mm. | Schistidium atrichum |
| 15 | Leaves mostly ovate-lanceolate, apices usually acute, usually greater than 1 mm; awns present in most species, sometimes absent; capsule usually greater than 0.7 mm | > 16 |
| 16 | Peristome absent, rudimentary, or very short (less than 100 µm) | > 17 |
| 16 | Peristome well-developed (greater than 200 µm) | > 19 |
| 17 | Leaves partially or completely 2-stratose distally; leaves moderately keeled distally; found only on calcareous rock. | Schistidium atrofuscum |
| 17 | Leaf lamina 1-stratose, rarely with a few 2-stratose striae; leaves strongly keeled distally; not restricted to calcareous rock | > 18 |
| 18 | Capsule usually campanulate; operculum rostrate; arctic species. | Schistidium cryptocarpum |
| 18 | Capsule cupulate; operculum mamillate; central North American species | Schistidium flaccidum |
| 19 | Peristome teeth long, to 700 µm, sometimes forming a dome; columella persistent in capsule, not falling with operculum. | Schistidium trichodon |
| 19 | Peristome teeth usually much shorter, never forming a dome; columella falling with operculum | > 20 |
| 20 | Plants small, often forming flattish cushions or tufts; awns very short to absent; capsule less than 1 mm, if taller then distinctly striate (S. dupretii) | > 21 |
| 20 | Plants small to large, usually forming rounded cushions, tufts, or mats; awns well developed, occasionally absent; capsules usually greater than 1 mm | > 23 |
| 21 | Basal marginal cells often elongate-rectangular; some central basal cells usually much lighter than adjacent cells, often hyaline; exothecial cells mostly oblate or isodiametric | Schistidium frigidum |
| 21 | Basal marginal cells quadrate or short-rectangular; basal cells evenly colored; many exothecial cells elongate | > 22 |
| 22 | Capsule ovoid or cupulate, rarely campanulate, rarely striate; basal marginal cells quadrate or short-rectangular, transverse walls usually thicker than longitudinal walls; plants compact, usually olivaceous. | Schistidium confertum |
| 22 | Capsule short-cylindrical, usually finely striate when empty; most basal marginal cells oblate, cell walls evenly thickened; plants open, usually brownish | Schistidium dupretii |
| 23 | The majority of exothecial cells of capsule wall elongate, sometimes mixed with isodiametric and, rarely, oblate cells | > 24 |
| 23 | The majority of exothecial cells more or less isodiametric, often mixed with oblate cells, elongate cells few or absent | > 27 |
| 24 | Leaves ovate-triangular, occasionally ovate-lanceolate, mostly well under 1.7 mm | > 25 |
| 24 | Leaves ovate-lanceolate, mostly greater than 2 mm | > 26 |
| 25 | Distal lamina 1-stratose, occasionally with 2-stratose striae or patches; awns usually absent; capsule light (yellow-) brown, usually narrowed towards the mouth. | Schistidium subjulaceum |
| 25 | Distal lamina with 2-stratose patches or 2-stratose; awns usually present; capsule red-brown, not narrowed towards the mouth. | Schistidium venetum |
| 26 | Leaf margins recurved to well below apex; distal lamina with 2-stratose patches or occasionally 2-stratose; distal laminal cells mostly rounded or short-rectangular, weakly sinuose; basal marginal cells longitudinally short-rectangular or quadrate. | Schistidium crassipilum |
| 26 | Leaf margins recurved to near apex; distal lamina 1-stratose, rarely with 2-stratose striae; distal laminal cells mostly short-rectangular, strongly sinuose; many basal marginal cells oblate. | Schistidium robustum |
| 27 | Capsule 0.4-0.8 mm; awns long, spinulose-denticulate; basal marginal cells with transverse walls thicker than longitudinal walls. | Schistidium liliputanum |
| 27 | Capsule usually 0.8 mm to 1.3 mm; awns short to long, weakly spinulose or nearly smooth; transverse basal marginal cells walls same thickness as longitudinal walls | > 28 |
| 28 | Leaves small, most well under 2 mm; costa smooth; some basal marginal cells elongate-rectangular; some basal cells usually much lighter than adjacent cells, often hyaline. | Schistidium frigidum |
| 28 | Leaves larger, usually greater than 2 mm; distal abaxial costa sometimes papillose; basal marginal cells quadrate or short-rectangular; basal cells the same color | > 29 |
| 29 | Distal leaf cells 11-14 µm wide; spores 15-21 µm; Arctic. | Schistidium grandirete |
| 29 | Distal leaf cells 8-10 µm wide; spores 11-15 µm, rarely larger; widespread | > 30 |
| 30 | Awns bright white, usually strongly decurrent; distal laminal cells variable in shape and size, strongly trigonous, often guttulate, occasionally, with stellate lumina, especially at mid leaf | Schistidium pulchrum |
| 30 | Awns dull and hyaline, strongly or non-decurrent; distal laminal cells more-or-less even in size and shape, trigones weak or absent, not guttulate or stellate | > 31 |
| 31 | Leaves ovate-lanceolate, erect or curved, rarely (falcate-)secund when dry, often greater than 2.4 mm; distal leaf margins usually denticulate; abaxial surface of costa usually papillose. | Schistidium apocarpum |
| 31 | Leaves narrowly ovate-lanceolate, usually curved, often falcate-secund when dry, less than 2.4 mm; distal leaf margins and costa smooth. | Schistidium flexipile |