Brachiaria dimorpha, A. Camus

Vorontsova, Maria S., 2022, Revision of some Malagasy forage grasses and their relatives within Brachiaria, Echinochloa, Moorochloa, and Urochloa, Candollea 77 (2), pp. 199-236 : 207-209

4. Brachiaria dimorpha A. Camus in Bull. Soc. Bot. F rance 72: 621. 1925 (F ig. 2E–F, 4).

Lectotypus (designated here): MADAGASCAR. Reg. Ihorombe [Prov. Fianarantsoa]: massif d’Andringitra , 2000 m, I.1923, Perrier de la Bâthie 14333 A et B [14333] ( P [ P03124753 ]!; isolecto-: K [ K000244728 ]!, P [ P03124768 , P03124773 ]!) . Syntypi: ibid. loco, 2400 m, II.1922, Perrier de la Bâthie 14333 A ( P [ P03124774 ]!); ibid. loco, 2300 m, II.1922, Perrier de la Bâthie 14333 B ( P [ P01973887 ]!) .

Stoloniferous mat-forming perennial, prostrate with ascending flowering culms, to 10 – 40 cm high, culms branched, rooting at nodes, glabrous. Leaf sheath glabrous or sparsely pubescent. Ligule a truncate membrane. Leaf blade lanceolate, thickly chartaceous, 0.8–3 × 0.1–0.4 cm, glabrous to pubescent on both sides. Inflorescence racemose, slender, contracted, 1.5–10 cm long. Racemes 1–5, 0.3– 3 cm long, much shorter than inflorescence axis, appressed, on a common axis 1–9 cm long, with no secondary branching, rhachis narrow, glabrous, spikelets overlapping with adjacent spikelets, paired, subsessile, on pedicels of uneven length. Spikelets somewhat laterally compressed, ovate, apically acute, 2.3–2.7 mm long, light green to purple. Lower glume ⅔–¾ as long as spikelet, membranous, keeled, acute to apiculate, 3–7-veined, glabrous to scaberulous, orientation relative to rhachis variable. Upper glume almost as long as spikelet, membranous, 3–5-veined, glabrous to sparsely pubescent. Lower floret male, palea as long as lemma, anthers 3, c. 1.5 mm long. Lower lemma membranous, 5-veined, glabrous to sparsely pubescent. Upper lemma acute, smooth, shiny, white to brown.

Distribution and ecology. – Endemic to the mountains of south-eastern Madagascar, open grassland and ericoid vegetation on rocks and by the sides of streams, peaty areas, often on gneiss, in areas protected from fire, at elevations of 1500–2500 m (F ig. 1).

Notes. – Brachiaria dimorpha is a distinctive species forming dense, almost moss-like cushions of vegetation with short erect inflorescences in open high elevation areas. This compact morphology changes in the shade under thickets of Erica L. to produce long leafy shoots. It is abundant and sometimes dominant on the 2000 m plateau of the Andringitra National Park. This species is shorter and grows at higher elections than its only known relative B. antsirabensis A. Camus , which shares its laterally compressed spikelets with short upper glumes.

There has been some confusion with the numbering of the original material by Perrier de la Bâthie. The protologue lists collections from three elevation ranges: up to 2000 (14333), 2300 (14333 B), and 2400 (14333 A). According to the label of P03124773 the numbers A and B were originally used by Perrier de la Bâthie to distinguish the plants he judged to be perennial ( A) and annual ( B). Herbarium sheets labels have three or four different numbers: 14333 A [ P03124774 ], 14333 B [ P01973887 ], 14333 A et B [ P03124753 , P03124768 , P03124773 ], and 14333 (duplicate outside P with the same data as A et B). The A and B sheets are annotated with the date F ebruary 1922, while A et B are annotated with January 1923 so it is possible that Perrier de la Bâthie later concluded that no distinction can be made between the annual and perennial plants. The lectotype designated here [ P03124753 ] is already labelled as type, has the most comprehensive material, and is labelled as A et B. The original material is here interpreted as three different collection numbers characterised by the three different elevations, following the protologue.

Selected specimens examined. – MADAGASCAR. Reg. Anosy [Prov. Toliara]: massif de l’Andohahela; vallée supérieure de la Sakamalio, I.1934, Humbert 13565 (P). Reg. Ihorombe [Prov. Fianarantsoa]: Sud-Andringitra, Andrianony, Manjarivolo, 2.XI.1970, Guillaumet 3491 (P); pic d’Ivohibe, XI.1924, Humbert 3311 (P); Massif de l’Andringitra, vallées de la Riambava et de l’Antsifotra, 27.XI.1924, Humbert 3697 (K, P); Andringitra NP, plateau E of camp 3, 13.XII.2013, Vorontsova et al. 1258 (K, TAN). Reg. Vakinankaratra [Prov. Antananarivo]: massif de l’Ibity, VI.1968, Morat 2862 (P).