Pelekium thomeanum (Broth.) Phephu

Phephu, Nonkululo, Rooy, Jacques Van & Van Wyk, Abraham E., 2013, New combinations and a key to the species of Pelekium (Thuidiaceae) in sub- Saharan Africa and the East African Islands, Phytotaxa 84 (2), pp. 60-64 : 60-63

Pelekium thomeanum (Broth.) Phephu stat. et comb. nov.

Basionym:— Thuidium involvens (Hedw.) Mitt. var. thomeanum Broth. (1890: 183) .

Other combinations:— Thuidium involvens subsp. thomeanum (Broth.) A. Touw (1976: 168) .

Cyrto-hypnum involvens subsp. thomeanum (Broth.) W.R.Buck & H.A.Crum (1990: 65) .

Type:— SAO TOMÉ. Queluz : 270 m, Quintas 1333a (holotype H, fide Touw (1976)) .

Description:— Plants medium-sized, pale green to yellowish green or brownish. Stems to 60 mm long, arching, 1or 2-pinnately branched. Paraphyllia many, simple to very weakly branched, short, mixed with long ones, to 15 cells long; cells oblong-rectangular or isodiametrical, sparingly papillose; terminal cell truncate, papillose. Axillary hairs with 1 brown basal and 1or 2 hyaline apical cells. Branches to 5 mm long, closely to remotely set; paraphyllia very few to lacking on branchlets. Leaves dimorphic, strongly incurved. Stem leaves 0.5–10 mm long, 0.25–0.6 mm wide, narrowly to broadly cordate-triangular, with patent base, plain to weakly plicate, closely set; when dry crisped, curved, concave, when wet spreading to widely patent. Apex gradually or abruptly short- to mostly long-acuminate, often twisted when dry. Costa strong, percurrent, ending in apex, tip indistinct, abaxially prominent, often grooved; cells smooth to very weakly papillose. Margins recurved to rarely plane below, plane upwards, papillate-crenulate. Terminal laminal cell truncate. Median cells 7–12 × 5–10 µm, short- to elongate-rhomboidal or -hexagonal, mainly unipapillose, some cells bi- to pluripapillose especially towards base; papillae weak or prominent, mostly central on lumen; cell walls thick or thin. Basal cells longer, larger, sometimes yellowish and smooth at insertion. Alar cells not differentiated. Branch leaves to 0.75 mm long, broadly rounded at base to narrowly ovate, asymmetrical, when dry strongly incurved, crisped, chain-like, with twisted apex and patent base, when wet spreading, complanate. Apex abruptly acute to short-acuminate. Margins recurved below, plane upwards, papillate-crenulate. Costa strong, abaxially weakly prominent, occasionally protruding in a distal spine. Terminal laminal cell truncate. Laminal cells to 6 µm wide, isodiametrical, mostly unipapillose, pluripapillose towards base, papillae low, indistinct.

Autoicous. Perigonia about 0.9 mm long; leaves ovate to broadly lanceolate; apex acute to abruptly longacuminate; costa strong to weak; entire to weakly serrate; cells isodiametrical, smooth, thick-walled; cells at insertion yellowish brown. Perichaetial inner leaves to 2 mm long; apex abruptly filiform, ending in subula; costa strong, filling subula; margins entire to serrulate, shoulders eciliate. Setae to 17 mm long, strongly roughened throughout, reddish. Capsules 0.6–1.5 mm long, ovoid to elliptic, weakly curved, horizontal to pendulous, constricted at neck, reddish brown. Exothecial cells quadrate, smooth; walls incrassate, collenchymatous. Peristome perfect; exostome teeth oblong-lanceolate, cross-striate below, papillose and trabeculate upwards, yellowish brown below, hyaline upwards; endostome membrane ½ the length of exostome; processes keeled (or carinate), narrowly perforate; endostome cilia in groups of 3, free. Operculum 1.0 mm long, long-rostrate. Calyptrae 1.5–1.7 mm long, cucullate, apex obtuse, smooth. Spores about 10–13 µm in diameter, papillose.

Diagnostic characters:—The species is recognised by 1-pinnately branched stems, simple to weakly branched, short or long paraphyllia with a truncate terminal cell, plain to weakly plicate stem leaves with gradually or abruptly acuminate short to long-acuminate apex, truncate terminal cell and unipapillose median cells, truncate branch leaf terminal cell, strongly roughened seta and eciliate inner perichaetial leaf shoulders.

Ecology and distribution:— Pelekium thomeanum is a lowland, forest bottom species growing in the rain forest zone or high forests, on tree bases, decaying wood, or occasionally terrestrial on soil and rocks, at 270–900 m, in light to dense shade. P. thomeanum is endemic to Africa and occurs in Angola, Cameroon, Central African Republic, Côte d’Ivoire, Congo, Equatorial Guinea ( Río Muni), Democratic Republic of Congo, Gabon, Ghana, Nigeria, Togo, and São Tomé. The lowland tropical American variant of P. involvens , namely P. involvens var. involvens , is known from Florida, Mexico, Ecuador, Bolivia, Venezuela and Brazil.

Specimens of P. thomeanum examined: — DEMOCRATIC REPUBLIC OF CONGO: Müller Z331 (L). CAMEROON: Argent AR.522 (BM); Dusen s.n. (NY); Sjostedt s.n. (NY); Staudt 711 (BM); Zenker 2008b (BM). NIGERIA: Barter 1424; (BM). ANGOLA: Junio 174 (BM). TANZANIA: Pócs & Pócs 6236/H (EGR).

Specimens of P. involvens examined: — DOMINICAN REPUBLIC: Allard 16142, 16168, 16209a, 17923a, 17958, (NY); Buck 4966, 4969, 5066, 5118 (NY); Reese 15051, 15496, 15560 (NY).

Notes: — Brotherus (1890) created an African variety ‘ thomeanum ’ of the American Thuidium involvens based on a Quintus 1333a specimen collected in São Tomé. Touw (1976) changed that variety to subspecies rank as Thuidium involvens subsp. thomeanum . Although Touw (1976) regarded the American and African taxa as forms of a single species with many plants showing intermediate characters, he ranked the African taxon as a subspecies because of its geographical isolation. He recently suggested that more American material be examined to decide the rank at which ‘ thomeanum ’ should be recognized (Touw, pers comm., 2010). In his notes, O’Shea (2006) suggested that the subspecies, like P. involvens , presumably belongs to Pelekium . We found that Thuidium involvens subsp. thomeanum resembles other medium- and small-sized species of Pelekium like P. varians (Welw. & Duby) Touw , P. chenagonii (Müll. Hal. ex Renauld & Cardot) Touw , P. ramusculosum (Mitt.) Touw and P. velatum Mitt. It resembles P. varians in many respects especially in the 1-pinnate branching. It is similar to P. velatum on account of eciliate perichaetial leaf shoulder margins and small spores.

The American P. involvens var. involvens and var. thomeanum are similar in respect to the 1-pinnately branching, strongly incurved stem leaves with long-acuminate apex, eciliate inner perichaetial leaf shoulder margins, and rough setae of equal lengths.

However the African plants differ from the American P. involvens in the latter having slightly shorter stems, shorter and unbranched paraphyllia, smaller stem and branch leaves, blunt branch leaf apex, plane stem leaves with entire margins and pluripapillose laminal cells, a slightly longer capsule, narrower and more curved when dry, and smaller spores.

Pelekium pseudoinvolvens (Müll. Hal.) Phephu comb. nov.

Basionym:— Hypnum pseudoinvolvens Müll. Hal. (1876: 285) .

Other combination:— Thuidium pseudoinvolvens A. Jaeger (1878: 254) .

Type:— COMOROS. Johanna: Anjouan, ad truncos arborum, 800 m, Hildebrandt 1835 (holotype B, lost; lectotype G, isolectotypes K, NY, fide Touw (1976); BM!) .

Description:— Plants medium-sized; yellow- or dark-green. Stems prostrate, about 55 mm long; 2-pinnately branched. Paraphyllia few, scattered to dense, mostly short, or long, to 11 cells long, mostly simple to moderately branched; cells mostly rectangular, smooth to papillose; terminal cell truncate, papillose. Axillary hairs of 1 hyaline basal and 2 brown apical cells. Branches to 5 mm long, remote, sparingly pinnate; branchlets remote and irregular; paraphyllia few basally to absent upwards, lacking on branchlets. Leaves dimorphic. Stem leaves distant, 0.4–0.6 mm long, 0.2–0.3 mm wide, triangular to subtriangular, plane to weakly plicate; when dry incurved, weakly spreading, appressed with long, incurved, flexuose or twisted apex; when wet erect spreading, concave, basally paraphyllate, short decurrent. Apex gradually narrowly short- to long-acuminate. Costa strong; percurrent, ending in apex, tip indistinct, abaxially prominent when dry, weakly so when moist. Margins irregularly plane or recurved, papillate-crenulate, bordered by a row of shorter or oblate cells. Terminal laminal cell truncate, occasionally acute papillose or smooth. Upper cells short to elongate, pluripapillose to smooth. Median cells 10–17 × 6 µm, short to long, variously angled hexagonal-rhomboidal, pluripapillose, 1 or 2 or rarely 3 papillae over lumina, papillae low or sharp, small, thin- to thick-walled. Basal cells larger, longer, smooth to pluripapillose; papillae low and blunt. Alar cells not differentiated. Branch leaves to 0.45 mm long, lanceolate, asymmetrical, when dry with spreading base and strongly incurved-twisted apex, when wet spreading to complanate. Apex acute to short-acuminate. Margins mostly plane to occasionally recurved, papillate-crenulate. Costa percurrent, tip distinct; abaxially prominent when dry, weakly or not when moist. Terminal laminal cell truncate and often larger than adjacent cells. Laminal cells to 6 µ m wide; short, variously angled or hexagonal, pluripapillose, papillae low, blunt, indistinct, crowded; walls incrassate. Basal cells larger, longer, pluripapillose to smooth.

Autoicous. Perigonia 0.5–1.0 mm long; leaves linear-lanceolate; apex mostly gradually filiform; margins plane or recurved, entire, serrate or papillose-crenulate; costa weak, percurrent; cells elongate-hexagonal or -rhombic, smooth to mostly papillose, thin-walled. Perichaetial inner leaves to 1 mm long, oblong-lanceolate; apex mostly gradually to abruptly subulate, erect or flexuose; margins plane, entire or weakly serrate, shoulders ciliate; cells linear-rhomboidal or rectangular, smooth or weakly unipapillose. Setae 6–8 mm long; strongly roughened throughout, brown. Capsules 0.5–0.7 mm long, ovoid, subpendulous, dark brown. Exothecial cells isodiametrical, quadrate or rounded, smooth; walls incrassate, collenchymatous. Peristome perfect; exostome teeth oblong-lanceolate, cross-striate and short-trabeculate below, becoming papillose, trabeculate and hyaline upwards; endostome shorter than exostome; membrane ½ the length of processes; processes weakly keeled, narrowly perforate upwards; endostome cilia in groups of 2 or 3, free. Operculum 1 mm long, short-rostrate, dark brown. Calyptra cucullate, smooth; apex acute, gradually mucronate. Spores 7–15 µm in diameter, papillose.

Diagnostic characters:—The species is recognised by the remotely 2-pinnately branched stems, short or long, simple to weakly branched paraphyllia with a truncate terminal cell, plane to weakly plicate stem leaves with gradually short to long-acuminate apex, truncate terminal laminal cell and uni- to bipapillose median cells, truncate branch leaf terminal cell, strongly roughened seta and ciliate inner perichaetial leaf shoulders.

Ecology and distribution:— Pelekium pseudoinvolvens is an epiphytic, lowland rain forest species growing on dead wood or tree trunks, at 450–800 m. It is endemic to Africa and has an East African islands distribution (Comoro, Mauritius, Madagascar and Mayotte). It is also reported to occur in Tanzania ( O’Shea, 2006) .

Notes:—After having studied the tropical Asian members of Pelekium, Touw (pers comm., 2010) questioned if P. pseudoinvolvens is really different from P. gratum (P. Beauv.) Touw. Although P. pseudoinvolvens is closely related to and sympatric with P. gratum , it differs from it in the weak, remotely bipinnate branching, stem paraphyllia less dense, paraphyllia cells longer and less papillose, often plane stem leaves with median and especially apical laminal cells elongated with thinner walls, papillae often less prominent, calyptra apex gradually mucronate, and exostome teeth broader and taller. These two species are similar in size, median cell ornamentation, inner perichaetial leaf shoulder margin and seta ornamentation. For consistency in the family, P. pseudoinvolvens , like the other small thuidioid species, should be classified under Pelekium as circumscribed by Touw (2001), where it is closely related to species like P. gratum .

Specimens examined:— MADAGASCAR: Marie s.n. (BM). COMOROS: Hildebrandt 1835 (BM). MAYOTTE: Marie 64, 85, 103, s.n. (BM). MAURITIUS: Robillard s.n. (BM).