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RHACITHECIACEAE

(B.J. O'Shea)

Plants small, solitary or more commonly forming short tufts. Stems erect, simple or few branched by innovations; radiculose below. Leaves crispate or curled when dry, erect-spreading when wet, mostly oblong to oblong-lanceolate or spathulate, acute to obtuse-rounded, apiculate or not; margins plane to erect or slightly incurved, entire or crenulate; costa single, 2/3 lamina length to short excurrent; median cells mostly subquadrate, occasionally rhomboid to short oblong-rectangular or hexagonal, smooth or pluripapillose; basal cells quadrate to more commonly oblong-rectangular, smooth, lax or not. Autoicous. Perichaetia terminal; leaves differentiated or not. Seta single, short to somewhat elongate, erect or curved, smooth. Capsule immersed to shortly exserted, urn short cylindrical, ovoid or subglobose, strongly 8-ribbed or not; stomata at base of urn, superficial; annulus often enlarged, persisting or deciduous. Operculum plano-mammillate to conic-apiculate or rostrate and often oblique. Peristome absent or if present then single, teeth 8 or 8 pairs, smooth or vertically ornamented. Calyptra cucullate to possibly mitrate, smooth or distally roughened, naked. Spores spherical to ellipsoid, granulate to finely papillose.

Discussion. The Rhachitheciaceae contain seven genera and 15 species distributed, in addition to Africa, in the tropical and subtropical areas of America and Asia; in Africa there are five genera and six species. The family, allied to the Orthotrichales, was reviewed recently by Goffinet (1998a), who provided a key for all species in the family, and interpreted the scattered and highly disjunct distribution of the family as indicating an ancient origin. A brief overview of the family in Africa appeared in O'Shea (1997). Characteristics of the family include the small plant stature, leaves oblong(-lanceolate) to broadly or narrowly spathulate, upper laminal cells mostly subquadrate, setae short, capsules immersed to short exserted and when present, peristome single with 8 teeth and urn strongly 8-ribbed. The family was established by Robinson (1964).

Literature. Goffinet, B. 1998a. The Rhachitheciaceae: Revised Circumscription and Ordinal Affinities. Bryologist 100: 425-439. O'Shea, B.J. 1997. British Bryological Society Expedition to Mulanje Mountain, Malawi. 9. Regmatodontaceae, Rhachitheciaceae, Rhacocarpaceae and Rhizogoniaceae (Bryopsida). Journal of Bryology 19: 805-813. Robinson, H. 1964. New taxa and new records of bryophytes from Mexico and Central America. Bryologist 67: 446-458.

Hypnodontopsis Z.Iwats. & Nog.

A single species occurs in Africa, H. mexicana (Thér.) H.Rob. from Uganda, which is also known from Mexico; the two other member of the genus are found in Japan and Burma (Myanmar). Akiyama & Tanaka (2002) suggest that the current distribution of the genus may be the remnants of what was once a wide distribution.

Plants small. Stems to 3 mm tall, few branched; weakly radiculose. Leaves crispate when dry, erect-spreading to spreading when wet, narrowly oblong-lanceolate, to 1.4 mm long, apex bluntly acute to obtuse-rounded; margins erect, entire; costa subpercurrent; lamina unistratose; upper cells irregularly quadrate-rounded, thick-walled, pluripapillose, papillae several over cell lumen; basal cells of the lower 1/4-1/3 differentiated, extending upward along margin a short distance, oblong-rectangular, smooth. Perichaetial leaves sheathing at base, to 1.5 mm long, otherwise similar to stem leaves. Seta curved or twisted when dry, curved when wet, ca. 1 mm long. Capsule slightly exserted, urn subcylindrical and strongly 8-ribbed when dry, ellipsoid when wet, ca. 0.6 mm long; exothecial cells differentiated between rib and inter-rib bands; stomata at urn base, superficial; annulus broad, deciduous. Operculum low conic, obliquely apiculate. Peristome single, teeth 8, coarse vertical markings below. Calyptra cucullate, smooth. Spores spherical, finely roughened.

Habitat. Epiphytic, on bark of trees; montane forests, at 2300 m elevation.

Discussion. The genus is characterised by narrowly oblong-lanceolate leaves, erect, entire margins, pluripapillose laminal cells, strongly 8-ribbed capsules, 8 peristome teeth coarsely vertical marked below, and obliquely apiculate low conic operculum. Our species is only known from a recent collection from Uganda (Hodgetts & Goffinet, 1998), a remarkable disjunction from the only other known collection in Mexico.

Literature. Akiyama, H. & Tanaka, A. 2002. Hypnodontopsis spathulata H.Akiyama & A.Tanaka (Rhachitheciaceae; Musci), a new species from Myanmar (Burma). Bryological Research 8: 131-136. [key to all 3 species] Hodgetts, N.G. & Goffinet, B. 1998. Hypnodontopsis mexicana (Thér.) H. Rob., a genus and species new to Africa. Journal of Bryology 20: 251-252. Iwatsuki, Z. 1957. The genus Hypnodon and its allies. Bryologist 60: 299-310.

Jonesiobryum B.H.Allen & Pursell

A single species, J. sphaerocarpum Bizot ex B.H.Allen & Pursell, is known from Nigeria and more recently from Central African Republic (Goffinet, 1998b); two additional species are recorded from Brazil.

Plants solitary or forming small tufts, yellowish-green. Stems to ca. 1 mm tall; in cross-section cells of nearly equal size, rather thin-walled, central strand weak; radiculose at base, rhizoids smooth. Leaves crowded, erect-appressed when dry, erect-spreading when wet, progressively larger above, oblong to obovate or orbicular, to ca. 1 mm long, apex bluntly acute to obtuse-rounded, margins erect to somewhat incurved, entire; costa strong below, subpercurrent to short excurrent; upper laminal cells irregularly subquadrate to rhomboid, smooth, thin-walled, rather lax; basal cells slightly differentiated, quadrate. Perichaetial leaves larger, obovate, to 1.3 mm long, apex bluntly acute and slightly reflexed, costa prominent on back. Seta very short, hardly observable. Capsule immersed, urn subglobose to broadly ovoid, to ca. 0.6 mm long; exothecial cells elongate, thin-walled; stomata at urn base, superficial or appearing slightly immersed; annulus well developed, persistent, ca. 3 outer layers of small isodiametric cells, inner row of much elongate narrowly oblong cells (to 55 µm long). Operculum plano-mammillate, ca. 0.2 mm long. Peristome absent. Calyptra not observed, possibly mitrate. Spores spherical, somewhat spaced coarsely papillose (granulate).

Habitat. Epiphytic, on trees, originally found on boles of Uapaca; in savanna woodlands, at elevations probably below 500 m.

Discussion The genus is characterised by oblong to obovate or orbicular leaves erect-appressed when dry, costa subpercurrent to short excurrent, smooth, little differentiated distal and proximal laminal cells, very short inconspicuous seta, subglobose capsule, large annulus, and absence of a peristome. Jonesiobryum has previously been placed in the Funariaceae: reasons for placement in the Rhachitheciaceae are explored in depth by Allen and Pursell (1991). Jonesia is an invalid name. The genus is named in honour of Eustace Wilkinson Jones (1909-1992), long time student of African bryophytes, particularly hepatics.

Literature. Allen, B. & Pursell, R.A. 1991. A reconsideration of the systematic position of Jonesiobryum. Bryologist 94: 438-442. Bizot, M., Pierrot, R.B. & Pócs, T. 1974. Trois genres nouveaux de Muscinées. Revue Bryologique & Lichénologique 40: 25-31. Goffinet, B. 1997b. Jonesiobryum sphaerocarpum Allen and Pursell (Musci: Rhachitheciaceae) new to the Central African Republic. Journal of Bryology 20: 242-243.

Rhachitheciopsis P.de la Varde

This monotypic genus is known only from R. tisserantii P.de la Varde (Potier de la Varde, 1926), from about five collections in Central African Republic.

Plants solitary or in tufts, green. Stems to 3 mm tall, branched; cells with wide lumens and thick walls, epidermal cells not differentiated, no central strand. Leaves spreading when moist, erect to spreading when dry, lingulate-spathulate, acute, to 1.4 mm long, 0.5 mm wide, margins plane, entire; costa strong, to 3/4 or 9/10 of lamina length, in transverse section with large, thin-walled, hyaline laminal cells, covering up to 5 abaxial layers of substereids; basal cells differentiated in lower third or half of the leaf, hyaline, subquadrate to mostly long rectangular, about twice as long as wide, moderately thick-walled, smooth; upper cells green, short, subquadrate to isodiametric, hexagonal, rather thin-walled, flat, smooth. Gemmae not seen. Perichaetial leaves weakly differentiated, erect-spreading, lingulate to lanceolate, with incurved margins near apex, apiculate, with costa filling most of the apiculus, to 1.7 mm long. Seta 1.5 mm long, erect and kinked upward when dry, twisted to right, curved downward when moist or capsule young. Capsule 0.8 mm long, eight-ribbed, broadly cup-shaped, exothecial cells 2:1, those forming ribs, yellowish, with very thick longitudinal anticlinal walls, stomata superficial, few, restricted to neck. Operculum slightly convex, lacking rostrum or mammilla. Peristome single, with 8 pairs of fused teeth; teeth incurved when moist, recurved when dry, smooth; annulus bistratose (two distinct layers), with both concentric layers uniseriate, caducous to persistent. Calyptra smooth, cucullate. Spores papillose.

Habitat. On trees and old wood.

Discussion. The genus is distinguished from Rhachithecium by the absence of a central strand in the stem, more than 2 layers of abaxial cells in the costa, a smooth calyptra, a bistratose annulus, papillose spores and a flat (not conic) operculum.

Literature. Potier de la Varde, R. 1926. Rhachitheciopsis P. de la V., genre nouveau d'Orthotrichacées de l'Afrique tropical. Bulletin de la Société Botanique de France 73: 74-76.

Rhachithecium Broth. ex Jolis

There is one widespread species in Africa, R. perpusillum (Thwaites & Mitt.) Broth. which is also widespread in Asia and the Neotropics, and a second R. welwitschii (Duby) R.H.Zander (doubtfully distinct from R. perpusillum) known only from one collection in Angola, which is said to have a double (rather than single) annulus. Rhachitheciopsis tisserantii P.de la Varde was considered by Robinson (1964 - see family ref.) to belong to this genus, but it was returned to Rhachitheciopsis by Goffinet (1998a - see family ref.). O'Shea (1997 - see family ref.) provides a key to species.

Plants solitary or forming short tufts, green or yellowish green. Stems short, to ca. 1 mm tall, with central strand; radiculose below. Leaves contorted and curled, lower leaves shorter and somewhat lingulate, upper leaves oblong-spathulate, to 2 mm long, apex obtuse-rounded or apiculate; margins plane, entire; costa strong below, to 2/3-4/5 lamina length, abaxial cells in 2 layers; lamina unistratose, laminal cells smooth, upper cells quadrate- to rectangular-rounded or irregularly hexagonal; basal 1/4 with cells laxly rectangular. Gemmae occasional, in upper leaf axils, obloid, multicellular. Perichaetial leaves strongly differentiated, erect-sheathing, narrowly oblong-lanceolate, to 2 mm or more long. Seta to 2.5 mm long, erect when dry, curved distally when wet, twisted. Capsule slightly exserted, urn cylindrical, to 1.2 mm long, strongly 8-ribbed when dry, ovoid to ellipsoid when wet, mouth flared when deoperculate; exothecial cells thin-walled; stomata at urn base, superficial; annulus unistratose, deciduous. Operculum conic or shortly rostrate, slightly oblique. Peristome single, set below mouth, reflexed when dry, inflexed when wet, teeth fused into 8 pairs, distally divided, smooth. Calyptra cucullate, papillose. Spores ellipsoid, finely punctate, appearing smooth.

Habitat. Epiphytic on bark of trees, apparently not an uncommon coloniser charred trees following fires, occasionally on rocks (see Jones, 1985 and O'Shea, 1997 - see family ref.); open savannas to moist woodland forests.

Discussion. The genus is characterised by the upper, oblong-spathulate leaves, curled-contorted when dry; costa 2/3-4/5 leaf length, smooth upper laminal cells, usually curved when wet, short seta ca. two times the urn length, cylindrical capsule, 8-ribbed when dry; smooth, distally divided into 8 paired peristome teeth.

Literature. Jones, E.W. 1985. Rhachithecium perpusillum (Thwait. & Mitt.) Broth. in Africa. Cryptogamie, Bryologique & Lichénologique 6: 47-50.

Tisserantiella P.de la Varde

A single species in Africa, T. pulchella (Thér. & Hilp.) R.H.Zander (syn. T. spathulata P.de la Varde) is known from Cameroon. A second species occurs in Brazil and Bolivia.

Plants forming short tufts, olive to yellowish green. Stems to 1-2 mm tall; weakly radiculose below. Leaves crowded, strongly crispate, contorted-incurved when dry, erect-spreading when wet, spathulate, to 1 mm long, somewhat channelled above, apex broadly obtuse-rounded; margins plane to cross-section stereids below guide cells; lamina unistratose, strongly differentiated with upper cells subquadrate, pluripapillose, papillae several over cell lumen, rather thick-walled; basal 1/4-1/3 with cells oblong-rectangular, smooth, lax. Perichaetial leaves somewhat differentiated, larger, to 1.85 mm long, apex often notched. Seta to ca. 2.3 mm long, slender. Capsule erect, urn ovoid to ovoid cylindrical, to 0.6 mm long; remaining features not observed (immature capsules). Operculum long rostrate, erect to somewhat oblique. Peristome stated to be absent. Calyptra not observed. Spores not observed.

Habitat. Epiphytic, on tree bark, apparently from semi-dry vegetation.

Discussion. The genus is distinguished by the spathulate leaves, crenulate margins, strongly differentiated upper, thick-walled, pluripapillose, isodiametric and lower lax, thin-walled smooth laminal cells, absence of a peristome, and long rostrate operculum. Zander (1993) excluded Tisserantiella in the treatment of the Pottiaceae, suggesting the Rhachitheciaceae, and this was confirmed by Goffinet (1998a - see family ref.).

Literature. Zander, R.H. 1993. Genera of the Pottiaceae: Mosses of Harsh Environments. Bulletin of the Buffalo Society of Natural Sciences, 32: 1-378.