Plagiochila angusta Lindenb.

Gradstein, S. Robbert & Reeb, Catherine, 2022, The genus Plagiochila (Dumort.) Dumort. (Marchantiophyta) in Madagascar, Cryptogamie, Bryologie 20 (5), pp. 65-106 : 70

Plagiochila angusta Lindenb.

( Fig. 1)

Plagiochila angusta Lindenb. , Species Hepathicarum (fasc. 5): 148 (1843). — Type: France. La Réunion, unknown collector, ex hb. Lehmann (holo-, UPS; fide Grolle 1995).

Plagiochila chenagona Steph. , Bulletin de la Société royale de Botanique de Belgique 31: 119 (1892).— Type: Madagascar ( Vanden Berghen 1981; Grolle 1995).

Plagiochila furcata Steph. , Bulletin de la Société royale de Botanique de Belgique 31: 120 (1892). — Type: Madagascar ( Vanden Berghen 1981).

Plagiochila pallida Gottsche, Abhandlungen des Naturwissenschaftlichen Vereins zu Bremen 7: 340 (1882). — Type: Madagascar ( Grolle 1995).

SPECIMENS EXAMINED. — Madagascar. Ambatovary forest, Imerina, Camboué s.n. (PC as P. calva det. Stephani; Dugas 1928). — Prov. Antananarivo • Mantasoa lake, III.1974, Onraedt 70M8155 (BR), 70M2047 (BR as P. angustitext a); Mandraka Forest Reserve, II.1974, Onraedt 70M2190 (BR); Ankazobe, Ambohitantely Reserve, IX.1994, Pócs 9444/J, Pócs 9444/M, Pócs 9444/N (EGR). — Prov. Antsiranana • Andasibe-Mantadia Nat. Park, III.1990, Pócs et al. 90104/ AM (EGR as P. repanda ); Amber Mountain Nat. Park, VIII.1973, Cremers 2760 (BR as P. furcata ); Manongarivo-Ambahatra Reserve, ridge of Ambahatra Mt., III.1999, Geissler 19849/1 (EGR, G); Marojejy Nat. Park, Andampibe valley, III.1990, Pócs 90112/J p.p. (EGR). — Prov. Fianarantsoa • Andringitra Nat. Park, VII.1955, Bosser 9629 (BR as P. cambuena , det. Vanden Berghen); ridge E of camp III, IX.1994, Pócs 9474/G (EGR); E of Korokoro river, Pócs 9476/F (EGR); Ranomafana Nat. Park, park gate near Ambodiamontana, VII.2004, Pócs et al. 04118/AZ (EGR, GOET), 04118/AW, 04118/AX, 04118/BA (EGR); Sahamalaotra Forest, near Vohipara, Pócs et al. 04120/BV (EGR, GOET), 04120/BS, 04120/BY (EGR); slope of Mt. Vatolampy, Pócs 04129/J (EGR); Sava, Makizovana massif, 420 m, Reeb 213D, 225 (PC). — Prov. Toamasina • near Andasibe (“Perinet”), c. 900 m, III.1974, Cremers 3124, 3126, 3169 (BR as P. furcata and P. angustitexta ); Andasibe-Mantadia Nat. Park, III.1990, Pócs et al. 90104/AM (EGR as P. repanda ); S of Andasibe-Mantadia Nat. Park, summit of Mt. Maromizaha, VIII.998, Pócs 9890/BQ (EGR).

ADDITIONAL SPECIMEN EXAMINED. — Madagascar. Without locality, Forsyth Major 100, syntype of P. gentiliana Steph. (G00068927; fide Grolle 1995).

DISTRIBUTION AND HABITAT. — East African Islands ( Madagascar, La Réunion). In Madagascar found on bark (tree trunks, branches, twigs) in the understory of humid to subhumid mid-elevation forests, between 500-1500 m.

DESCRIPTION (see also Vanden Berghen 1981 as Plagiochila chenagona )

Plants 2-4 mm wide, to 10 cm long, long and slender, dichotomously branched, branches terminal, occasionally intercalary on broken stems, rhizome-like creeping shoot present. Leaves contiguous to imbricate, branch leaves suberect (spreading at angles of c. 15-30° with the stem), slightly ampliate, very asymmetrically ovate-oblong, to 0.5 mm long, c. 1.5-2× longer than wide, apical margin with 3-5 teeth with the central tooth being largest, margins and bases otherwise entire; leaves towards stem bases more widely, obliquely spreading and distinctly ampliate, ovate-subrectangular with a broad rounded apex, c. 1.2-1.4× longer than wide, margins entire or with a few irregular, small teeth (up to 10); dorsal leaf bases shortly to longly decurrent, swollen, with elongate cells, not concealing the stem, ventral leaf bases shortly and very narrowly decurrent, decurrent ventral part to 0.2 mm long, entire. Leaf cells irregularly (sub)isodiametrical to slightly elongate in midleaf, c. 15-25µm wide in midleaf, trigones rather small, cordate or slightly swollen, sometimes confluent, cells towards the leaf margin smaller, subrectangular, in basal stem leaves sometimes thicker-walled and forming a weak, yellowish, 1-3 cells wide, cells towards the swollen dorsal leaf base frequently elongate, rectangular, but not elongate towards the midbasal portion of the leaf, vitta-like region absent; cuticle smooth; oil bodies not observed. Underleaves absent. Androecia intercalary, with 5-10 pairs of bracts. Perianth without stalk, perianth mouth conspicuously and longly laciniate. Vegetative reproduction not observed.

NOTES

Plagiochila angusta (sect. Vagae Lindenb.) is distinguished by the long and flaccid, mostly dichotomously branched plants (branching terminal) with suberect to obliquely spreading branch leaves with a few teeth at apex and more widely spreading, ampliate stem leaves with almost fully entire margins. The contrast between suberect, toothed branch leaves and more widely spreading, subentire stem leaves usually allows to recognize the species at a glance. However, populations may occur in which the difference between branch and stem leaves is not very pronounced (e.g. plants from Forêt d’Ambatovary collected by Camboué and identified by Stephani as P. calva ). The leaf cells in P. angusta are rather small, c. 15-25 µm wide in midleaf, with small, cordate or slightly swollen trigones; the cells are sometimes conspicuously elongate towards the swollen dorsal base, but not towards the midbasal portion (vitta-like area absent); stem leaves of robust plants are sometimes bordered by small, thicker-walled cells in 1-3 rows.

The stem leaves of P.angusta may resemble those of P.repanda , but in the latter species they are more widely spreading and the trigones are much larger and strongly swollen. Moreover, branches of P. repanda are very few and mostly intercalary, very rarely terminal.