Urochloa humbertiana (A. Camus) Voronts.

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 : 227-228

22. Urochloa humbertiana (A. Camus) Voronts. , comb. nov.

Brachiaria humbertiana A. Camus in Bull. Soc. Bot. F rance 79: 844. 1933.

Lectotypus (designated here): MADAGASCAR. Reg. Atsimo-Andrefana [Prov. Toliara]: E du delta de la Linta, Beharahaka, VIII.1928, Humbert & Swingle 5487 ( P [ P00450180 ]!; isolecto-: P [ P00450181 ]!) . Syntypi: MADAGASCAR. Reg. Androy [Prov. Toliara]: Ambovombe, II.1931, Decary 8466 ( P [ P02210586 ]!); Ambovombe , II.1931, Decary 8546 ( K [ K000805655 ]!; P [ P02233594 ]!) . Reg. Anosy [Prov. Toliara]: vallée du Mandrare à Amboasary, I .1932, Decary 9564 ( P [ P02210587 ]!) . Reg. Atsimo-Andrefana [Prov. Toliara]: dunes de Tulear, V .1910, Perrier de la Bâthie 11188 ( P [ P02210588 , P02233560 ]!) .

Loosely tufted perennial, with short knotty rhizomes, ascending to erect, to 0.5 m high, culms branched at base, rooting at lower nodes, glabrous to shortly pilose. Leaf sheath glabrous or sometimes pilose. Ligule a lacerate ciliolate membrane. Leaf blade linear, sometimes narrow-lanceolate, chartaceous, 2.5– 10 × 0.1 –0.5 cm, glabrous to pubescent on both sides. Inflorescence racemose, slender, open or contracted, 5–10 cm long. Racemes 3–7, 1–5 cm long, flexuous, decreasing in length upwards, lowermost raceme roughly equal to inflorescence axis in length, on a common axis 2–6 cm long, with no secondary branching, rhachis narrow, scabrous, spikelets not overlapping with adjacent spikelets, single, on pedicels of uneven length. Spikelets oblong to somewhat obovate, apically subacute, 2–3 mm long, whiteish. Lower glume c. ⅓ as long as spikelet, membranous, obtuse, 1–3-veined, glabrous or sometimes pilose, separated from rest of spikelet by an internode c. 0.5 mm long, orientation relative to rhachis variable. Upper glume as long as spikelet, herbaceous, 5-veined, veins dark green, glabrous or sometimes pilose. Lower floret infertile or male, palea c. ⅔ to as long as lemma, anthers 3, c. 2 mm long. Lower lemma herbaceous, 5-veined, glabrous or sometimes pilose. Upper lemma subacute, finely rugose to almost smooth.

Distribution and ecology. – Endemic to southern Madagascar and abundant in southern spiny forest, in both primary and secondary vegetation, at elevations of 0–750 m. F requently found on dunes by the sea (F ig. 15) .

Notes. – Urochloa humbertiana (A. Camus) Voronts. can usually be recognised by its unusually narrow linear leaf blades 1–3 mm wide; these sometimes become lanceolate up to 5 mm wide. Its lower glume is translucent with almost invisible veins, while the 5 veins on upper glume and the lower lemma are a clearly visible dark green colour. The species U. humbertiana encompasses considerable variability in leaf width (usually narrow and linear, sometimes broader and narrow-lanceolate), indumentum (leaf blades and spikelets usually glabrous but sometimes pilose), and fertility of the lower floret (usually sterile with palea c. ⅔ as long as the lower lemma, sometimes male with 3 anthers and palea as long as the lemma). Individuals with broad leaf blades, indumentum, and fertile lower florets (e.g. Bosser 14626 and Nanjarisoa et al. 192) are substantially different in appearance but do not seem to justify the description of a new species.

The lectotype is chosen for its superior quality material and annotation by the author.

Selected specimens examined. – MADAGASCAR. Reg. Androy [Prov. Toliara]: Beloha , III.1960, Bosser 14149 ( P). Reg. Anosy [Prov. Toliara]: vallée de la Manambolo au NW de Maroaomby, XII.1933, Humbert 12771 ( K, P, TAN). Reg. Atsimo-Andrefana [Prov. Toliara]: 32 km au N de Tuléar, Madiorano , forêt de M. Domergue , 31.I.1990, Labat & Du Puy 2037 ( K, P); plateau Mahafaly , s.d., Perrier de la Bâthie 115 ( K); Berenty , 10 km from Amboasary west , 16.III.2019, Rakotomalala et al. 289 ( K, TAN) .