Plagiochila vandenberghenii Gradst. 2022, sp. nov.
Creators: name: Gradstein, S. Robbert
name: Reeb, Catherine
Publisher: name: Zenodo
Year: 2022
Subjects: Biodiversity
Taxonomy
Plantae
Marchantiophyta
Jungermanniopsida
Jungermanniales
Plagiochilaceae
Plagiochila
Plagiochila vandenberghenii

description: Plagiochila vandenberghenii Gradst., sp. nov.   (Fig. 23)  
 Plagiochila vandenberghenii Gradst., sp. nov. (sect. Vagae) stands out by irregularly pinnate to dichotomous branching by terminal and intercalary branches, and somewhat distant, horizontally spreading, narrowly oblong-rectangular, non-ampliate leaves (c. 2.5-3× longer than wide) with the apex bifid by two large, lobe-like teeth, and a slightly bordered leaf margin with more elongate cells in 1-2 rows; 2-5 additional, smaller teeth are produced at the leaf apex and on the distal half of the ventral and dorsal margin. Underleaves are absent.   
 HOLOTYPE. — Madagascar. Prov. Fianarantsoa • Ranomafana Nat. Park, opposite park gate, near Ambodiamontana settlement, Namorona river valley, on bark in partially degraded lower montane rainforest, 865-1015 m, VII.2004, Pócs et al. 04118/AY (holo-, EGR!; iso-, GOET!).   
 ADDITIONAL SPECIMEN EXAMINED. — Madagascar. Prov. Fianarantsoa • Ranomafana Nat. Park, near park gate, 1067 m, on twigs, Reeb CR 17 M 610 (PC).   
 ETYMOLOGY. — Named after the late Professor Constant Vanden Berghen, renowned Belgian botanist and bryologist who has laid the basis for our knowledge of Plagiochila in Madagascar.   
DISTRIBUTION AND HABITAT. — Only known from Ranomafana National Park (two collections) on Madagascar, growing on bark.  DESCRIPTION  
Plants 3-4 mm wide, to 4 cm long, irregularly branched below and on broken shoots by intercalary branches, dichotomous above by terminal branches, rhizome-like creeping shoot present. Mature stem leaves distant to contiguous, widely and horizontally spreading (not ventrad), narrowly and subsymmetrically oblong-rectangular, 2.5-3× longer than wide, on branches up to 4× longer than wide, not caducous, not ampliate and not shouldered, margins almost parallel, unbordered or weakly bordered, with 5-8 teeth in the upper half made up of rectangular cells; leaf apex bifid by two long, lobe-like teeth, to 10-15 cells long, the two teeth separated by a wide rounded sinus, sometimes one of the two teeth is broken, a smaller tooth may be present in the sinus between the two large lobe-like teeth and occasionally the apex is trifid, tip cell of the teeth not much longer than the rest of the cells, distal portion of ventral and dorsal leaf margin with 1-3 smaller teeth, lower half of the margins and bases entire; leaf bases shortly and narrowly decurrent, the decurrent ventral part maximally 0.15 mm long. Leaf cells subisodiametrical to slightly elongate, 1-1.5× longer than wide, 18-30 µm wide in midleaf, trigones small but not swollen, triangular with concave walls and frequently radiate along the longer walls, cells along the margin sometimes more elongate and with a thicker inner tangential wall, forming a weak border, leaf base without vitta-like area, cuticle smooth; oil bodies not observed. Underleaves absent. Androecia not seen. Perianth campanulate, slightly elevated above the bracts on a short, thickened stalk. Vegetative reproduction not seen.  NOTES  
 Plagiochila vandenberghenii Gradst., sp. nov. (sect. Vagae) is readily distinguished from all other African members of the genus Plagiochila by the horizontally spreading, narrowly oblong-rectangular, non-ampliate leaves (c. 2.5-3× longer than wide) with a strongly bifid apex, with two long teeth. In its horizontally spreading, bifid leaves, the new species cannot be confused with any other African species of Plagiochila and only resembles the Asian P. bicornuta Steph. (synonym: P. laxissima Schiffn.; fide So 2001), but the apical teeth in latter species are smaller and terminal branching is lacking.   
B C A D G E F H I J K L M  
 The perianths in the new species are campanulate.According to Heinrichs (2002), campanulate perianths are characteristic of unfertilized gynoecia, but the perianths in P. vandenberghenii Gradst., sp. nov. had mature sporophytes.
description: Published as part of Gradstein, S. Robbert & Reeb, Catherine, 2022, The genus Plagiochila (Dumort.) Dumort. (Marchantiophyta) in Madagascar, pp. 65-106 in Cryptogamie, Bryologie 20 (5) on pages 102-104, DOI: 10.5252/cryptogamie-bryologie2022v43a5, http://zenodo.org/record/12215006