KEY TO SPECIES OF PLagIOchILa (DUMORT.) DUMORT. FROM MADAGASCAR 1. Ventral leaf margin undulate. Leaves ampliate, ventrad............................................................................... 2 — Ventral leaf margin not undulate (or slightly undulate at the base only). Leaves ampliate or not ampliate, horizontally spreading or ventrad....................................................................................................................... 4 2. Ventral leaf base shortly and narrowly decurrent, the decurrent strip linear, less than 0.2 mm long, entire, not undulate. Underleaves absent. Ventral leaf margin undulate and sometimes with long and sharp teeth. Leaf cells 10-20 µm wide in midleaf, with large confluent trigones and strongly angular-undulate lumina............................................................................................................................................................ P. rodriguezii Steph. — Ventral leaf base longly and broadly decurrent, the decurrent strip broadly lanceolate, more than 0.2 mm long, undulate and usually ciliate-laciniate. Underleaves present. Ventral leaf margin undulate, without long and sharp teeth. Leaf cells slightly larger, 18-25 µm wide in midleaf, trigones not confluent, lumina not strongly angular-undulate......................................................................................................................................... 3 3. Ventral stem surface with paraphyllia between leaf bases, the paraphyllia very small, consisting of short rows of rounded cells. Ventral leaf margin undulate in the lower half............................................ P. squamulosa Mitt. — Ventral stem surface without paraphyllia. Ventral leaf margin usually undulate over its entire length................................................................................................................................ P. corrugata (Nees) Nees & Mont. 4. Some or all dorsal leaf bases toothed............................................................................................................ 5 — Dorsal leaf bases entire................................................................................................................................ 6 5. Dorsal stem surface with paraphyllia (between the leaf bases). Leaves falcato-secund, subtransverse to obliquely spreading............................................................................................................................... P. sikorae Steph. — Dorsal stem surface without paraphyllia. Leaves obliquely to widely spreading, not falcato-secund................................................................................................................................................................ P. barteri Mitt. 6. Leaves conspicuously falcate and strongly elongate, leaf apex with two very long, dívaricate teeth. Leaf cells 1.5- 2× longer than wide............................................................................................. P. drepanophylla Sande Lac. — Leaves not conspicuously falcate and elongate, leaf apex bifid or not bifid. Leaf cells less elongate............... 7 7. Stem leaves ± ampliate, 1-2-2.5)× longer than wide..................................................................................... 8 — Stem leaves not ampliate, 2-3× longer than wide (when in doubt try both leads)....................................... 15 8. Branch leaves suberect, stem leaves spreading outwards (obliquely). Stem leaves ± entire......................................................................................................................................................................... P. angusta Lindenb. — All leaves spreading outwards. Stem leaves usually toothed (± entire in P. repanda var. repanda)................... 9 9. Leaf cells very large, 35-50 µm wide in midleaf. Plants robust, 5-9 mm wide. Rare species on Madagascar....................................................................................................................................................................... 10 — Leaf cells smaller. Plants 2-5(-6) mm wide. Common species on Madagascar............................................ 11 10. Leaves alternate. Teeth linear, small, 2-5 cells long, 1-2 cells wide at the base. All or part of the leaf cells at least papillose by small rounded papillae..................................................................................... P. boryana Steph. — Leaves subopposite. Teeth triangular, large, 4-8 cells long, 3-6 cells wide at the base. All leaf cells smooth....................................................................................................................................... P. macrostachy a Lindenb. 11. Ventral leaf margin entire. Leaf apex entire or with a few small teeth (not bifid)................................................................................................................................................ P. repanda (Schwägr.) Lindenb. var. repanda — Ventral leaf margin toothed. Leaf apex toothed, sometimes bifid............................................................... 12 12. Leaves horizontally spreading. Trigones large and swollen, or small and not swollen. Cells in the dorsal leaf bases not elongate.............................................................................................................................................. 13 — Leaves ventrad. Trigones small, not or scarcely swollen. Cells in the dorsal leaf bases sometimes elongate......................................................................................................................................................................... 14 13. Leaf cells rather small, 15-25 µm wide in midleaf (leaves not very transparent), trigones strongly swollen and becoming confluent at the leaf margin, margin cells usually thicker-walled. Leaf apex mostly bifid............................................................................................................ P. repanda var. perrotana (Steph.) Vanden Bergh. — Leaf cells larger, (20-)25-30 µm wide in midleaf (leaves more transparent), trigones not or hardly swollen, not confluent at the margin, margin cells not thicker-walled. Leaf apex bifid or not bifid................................................................................................................................................................................... P. incerta Steph. 14. Leaves narrowly oblong, (1.5-)2-3× longer than wide, teeth on leaf margins often terminating in a very long, 2-4× longer than wide cell. Cells in the dorsal bases of stem leaves not conspicuously elongate............................................................................................................................................................. P. terebrans Lindenb. — Leaves less elongate, 1.3-2× longer than wide, teeth terminating in a shorter cell. Cells in the dorsal bases of stem leaves often conspicuously elongate............................................................................ P. kiaeri Gottsche 15. Terminal branches present (sometimes only few, in the upper part of the plant)........................................ 16 — Terminal branches absent.......................................................................................................................... 19 16. Leaf apex strongly bifid, the apical teeth to 15 cells long. Leaves horizontally spreading. Rare montane species................................................................................................................ P. vandenberghenii Gradst., sp. nov. — Leaf apex entire or toothed, not strongly bifid. Leaves ventrad or horizontally spreading........................... 17 17. Leaves ventrad. Plants irregularly pinnate in the lower part and dichotomous in the upper part (or purely pinnate). Underleaves absent. Common species in montane environments.......................... P. terebrans Lindenb. — Leaves horizontally spreading. Plants purely dichotomous. Underleaves present. Rare lowland species...... 18 18. Leaf margins entire or with 1-4 short teeth (1-3 cells long) at apex. Leaf cells c. 15-20 µm wide in midleaf, thin-walled. In coastal rainforest, rare...................................................................................... P. strictifolia Steph. — Apical and ventral leaf margin with 15-20 long teeth (3-10 cells long). Leaf cells larger, c. 25 µm wide in midleaf, ± thick-walled with radiate trigones. Occurrence on Madagascar to be confirmed ............................................................................................................................................................................... P. boivinii Steph. 19. Leaves fragmenting, upper part of leaf frequently broken away.................................................................. 20 — Leaves not fragmenting, but sometimes caducous...................................................................................... 21 20. Leaves horizontally spreading, narrowly oblong, 2-3× longer than wide, fragmenting near the apex. Leaf margins entire or with 2-4 blunt lobes at the apex................................................................................... P. fracta Pócs — Leaves subtransverse, 1.5-2× longer than wide, fragmenting in the lower half. Leaf margins with 4-7 sharp teeth in the upper half (teeth at apex largest)..................................................................... P. bifaria (Sw.) Lindenb. 21. Mature stem leaves 2-3× longer than wide, narrowly oblong to ligulate to rectangular... P. pectinata Lindenb. — Mature stem leaves 1-2× longer than wide, suborbicular to (ob)ovate-oblong to ovate-rectangular [when in doubt try both leads]................................................................................................................................. 22 22. Caducous leaves present............................................................................................................................ 23 — Caducous leaves absent............................................................................................................................. 25 23. Leaves oblong, widest in the middle, 1.5-2× longer than wide. Trigones small, not bulging. Leaf base without vitta-like area of larger cells. Plants without leafless, stoloniform shoots. Perianth with a short stalk at the base................................................................................................................................ P. simplex (Sw.) Lindenb. — Leaves obovate, widest above the middle, 1-1.5(-2)× longer than wide. Trigones of stem leaves large, bulging. Leaf base with a vitta-like area. Plants often with leafless, stoloniform shoots (due to caducous leaves). Perianth without stalk at the base............................................................................................................................ 24 24. Leaves 1-1.3× longer than wide, toothed at apex and along the ventral margin........................................................................................................................................................ P. punctata (Taylor) Taylor var. punctata — Leaves more elongate, 1.3-2× longer than wide, entire or with a few small teeth at apex............................................................................................ P. punctata var. paucidentata (Mont. & Gottsche) Gradst., comb. nov. 25. Leaf apex bifid. Plants small, 1.5-2 mm wide. Lowlandslender phenotype of.............................................................................................................................................. P. repanda var. perrotana (Steph.) Vanden Bergh. — Leaf apex not bifid. Plants 2-5 mm wide. Lowland or montane................................................................. 26 26. Plants 2-3.5 mm wide. Leaves narrowed to the apex, toothed at the apex and along most of the ventral margin. Cuticle ± papillose. Leaf base with a vitta-like area of larger cells........................................ P. stricta Lindenb. — Plants larger, 4-5 mm wide. Leaves not narrowed to the apex (apex broadly rounded), with very small teeth near the apex. Cuticle smooth. Leaf base without vitta-like area............................................. P. integerrima Steph.

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 67-68, DOI: 10.5252/cryptogamie-bryologie2022v43a5, http://zenodo.org/record/12215006