Brachiaria subrostrata 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 : 213

9. Brachiaria subrostrata A. Camus in Bull. Soc. Bot. F rance 73: 691. 1927 (F ig. 7, 8A–B).

Lectotypus (designated here): MADAGASCAR. Reg. Vakinankaratra [Prov. Antananarivo]: Betafo , bords de chemins, 1200 m, III.1920, Perrier de la Bâthie 13064 ( P [ P00450190 ]!; isolecto-: K [ K000244725 , K000244726 ]!, P [ P00450191 , P00450192 ]!) . Syntypus: MADAGASCAR. Reg. Analamanga [Prov. Antananarivo]: Tananarive , III.1921, Perrier de la Bâthie 13661 ( P [ P01914074 , P00450193 , P00450194 , P00450195 ]!) .

Stoloniferous mat-forming perennial, prostrate with ascending flowering culms, to 7– 10 cm high, culms branched at base, rooting at lower nodes, glabrous, nodes bearded. Leaf sheath pilose. Ligule a line of hairs. Leaf blade narrowly lanceolate, chartaceous, 1.5 – 7 × 0.3 – 0.7 cm, pilose on both sides. Inflorescence racemose, subcapitate, on a pilose peduncle, 1.5–3.5 cm long. Racemes 2–5, 0.5–2 cm long, appressed, decreasing in length upwards, on a common axis 0.5– 2 cm long, with no secondary branching, rhachis triquetrous, scaberulous with some long cilia, spikelets overlapping untidily with adjacent spikelets, single or paired, on pedicels of uneven length. Spikelets obovate, apically acuminate, 3–3.5 mm long, green, with a prominent ciliate rim ⅔ from base. Lower glume c. ¼ as long as spikelet, membranous, rounded to acute, with no venation, glabrous to pubescent, orientation relative to rhachis variable. Upper glume as long as spikelet, herbaceous, long-acuminate, 5–7-veined, veins green and prominent, with cross veins near apex, with short white trichomes in lower part and dense white trichomes 1–2 mm long on the rim. Lower floret infertile, palea c. ⅓ as long as spikelet. Lower lemma herbaceous, long-acuminate, 5-veined, with short white trichomes in lower part and dense white trichomes 1–2 mm long on rim. Upper lemma obtuse, minutely striate.

Distribution and ecology. – Common component of moist highland roadside grazing lawns. Known only from lawns, grazed or otherwise physically disturbed open ecosystems, hence associated with human habitation, at elevations of 1200–1600 m (F ig. 9).

Notes. – Range restricted but commonly encountered aesthetically appealing species easily recognisable by a ciliate rim clearly visible on the apical parts of its spikelets. The spikelets detach as a single unit just below the glumes, and the spreadout cilia are likely involved in the seed dispersal process (F ig. 7, 8A–B).

The morphology of Brachiaria subrostrata A. Camus is fairly similar to its closest relatives in the chloroplast marker phylogeny by HACKEL et al. (2018): the abundant B. umbellata (Trin.) Clayton with glabrous spikelets, and the annual Yvesia madagascariensis A. Camus. These are likely to fall in the same clade as the rare endemic annual Brachiaria perrieri A. Camus , which also has attractive long cilia on its spikelets, in common with B. subrostrata and Yvesia madagascariensis. Brachiaria subrostrata roots at the nodes and seems to flower early on in its life cycle, and is also frequently recorded as annual. These four species could potentially be assigned to a new genus once thorough sampling of continental African Brachiaria is added to the analyses.

The lectotype is selected for its best quality flowering material and broadest duplicate distribution. The syntype collection Perrier de la Bâthie 13661 bears an original note “probablement d’introduction récente” which likely reflects Perrier’s erroneous assumption that roadside plants are not native. It is not included in his inventory of plants introduced to Madagascar (PERRIER DE LA BÂTHIE, 1931, 1932), and is acknowledged as endemic by both CAMUS (1927) and Bosser (1969) .

Selected specimens examined. – MADAGASCAR. Reg. Analamanga [Prov. Antananarivo]: rte. de Manankavaly, III.1959, Bosser 12860 ( P) ; env. de Tananarive , PK 13 rte. de Tamatave, II.1969, Bosser 19298 ( P) ; Antananarivo centre , V.1903, Perrier de la Bâthie 15805 ( P) ; Tzimbazaza , outside the herbarium building, 22.II.2013, Vorontsova & Besnard 988 ( K, TAN) ; Antananarivo-ville , I.1916, Waterlot s.n. ( P) . Reg. Vakinankaratra [Prov. Antananarivo]: Manandona , 2.V.2014, Nanjarisoa et al. 218 ( K, TAN) ; Antsirabe II , Vinanikarena village , 5.III.2017, Solofondranohatra et al. 803 ( K, P, TAN) ; Ambohimandroso , Analamahitsy village , 26.IV.2017, Solofondranohatra et al. 884 ( K, P, TAN) ; road to Ibity PA from Antsirabe , 28.II.2019, Vorontsova et al. 2397 ( K, TAN) .