Panicum humbertii A. Camus

Vorontsova, Maria S., 2018, Revision of the group previously known as Panicum L. (Poaceae: Panicoideae) in Madagascar, Candollea 73 (2), pp. 143-186 : 162

13. Panicum humbertii A. Camus in Bull. Soc. Bot. France 72: 620. 1925.

Lectotypus (designated here): MADAGASCAR. Prov. Antsiranana: Massif de Manongarivo, IV.1909, Perrier de la Bâthie 11088 ( P [ P00450267 ]!; isolectotype: P [ P00450268 ]!) .

= Panicum muscicola A. Camus in Bull. Soc. Bot. France 94: 40. 1947 [ as muscicolum]. Lectotypus (designated here): MADAGASCAR. Prov. Antsiranana: Montagne d’Ambre, VIII.1933, Perrier de la Bâthie 19300 ( P [ P00450256 ]!; isolectotype: P [ P02263028 ]!).

= Panicum calcicola A. Camus in Bull. Soc. Bot. France 94: 39. 1947 [as calcicolum]. Lectotypus (designated here): MADAGASCAR. Prov. Antsiranana: Montagne des Français, V.1923, Perrier de la Bâthie 16209 ( P [ P00450281 ]!; isolectotype: P [ P00450279 , P00450280 ]!).

Scandent perennial woody at base, rooting at nodes, to 2 m long, the culms glabrous, the nodes dark and glabrous. Leaf sheaths glabrous, with bulbous-based hairs on the margins. Ligule membranous, obtuse. Leaf blades lanceolate, often asymmetric at base, flat, membranous, 4– 15 × 1 –2.5 cm, drying green-brown, cross veins visible when dry, glabrous to sparsely pubescent on both sides, sometimes with bulbous based cilia on the lower part of the margin. Panicles terminal, partly exserted, (5–) 15–20 cm long, effuse, the branches dehiscent, appressed when young and becoming broadly divergent at maturity, usually with a dense cover of bulbous-based white cilia several times longer than the spikelet. Spikelets elliptic, apically acute, 1 – 1.4 mm long, brown, never gaping open. Lower glume c. 2/3 as long as the spikelet, membranous, acute, 3-veined, with small prickle hairs. Upper glume usually as long as the spikelet, sometimes 2/3–3/4 as long, herbaceous, (3–)5- veined, with small prickle hairs, dehiscing early. Lower floret barren, without a significant palea. Lower lemma herbaceous, 5-veined, with small prickle hairs. Upper lemma smooth, shiny, brown.

Distribution and ecology. – Endemic to northern Madagascar seasonally dry forest on limestone and gneiss, 250–1200 m ( Fig. 8B ). Seems to be rare; an expedition by the author in 2015 failed to locate this species.

Notes. – This species has dehiscent inflorescence branches, a rare character in grasses. Panicle branches are appressed to the axis on emergence. As the inflorescence ages the upper branches of the inflorescence dehisce, leaving broadly divergent lower inflorescence branches. Hirsute inflorescence branches can form a tangled mass (Wohlhauser & Andriamalaza 60285) which may attach itself to passing animals. Spikelets are similar to Cyrtococcum multinode (Lam.) Clayton but not dorsally compressed, the spikelets are single, and panicle branches almost always have long white hairs. Panicum muscicola is a variant with no trichomes in the inflorescence. Inflorescences of P. humbertii are at least 10 cm long; a single collection Bosser 20382 has inflorescences c. 5 cm long, likely associated with a particularly dry habitat.

The lectotypes of P. humbertii , P. muscicola and P. calcicola are chosen for their superior flowering material.

Additional material examined. – MADAGASCAR. Prov. Antsiranana: Montagne d’Ambre , VII.1953, Bosser 5342 ( P [ P02608857 ], TAN) ; ibid. loco, VII.1953, Bosser 5379 ( P [ P02263027 ]) ; ibid. loco, VII.1953, Bosser 5543 ( K [ K000805468 ], P [ P02222308 ]) ; montagne des Francais , 13.IV.1970, Bosser 20162 ( P [ P06795924 ]) ; ibid. loco, 13.IV.1970, Bosser 20169 ( P [ P06795925 ]) ; forêt de Sahafary , VI.1970, Bosser 20382a ( P [ P02222320 ]) ; NE d’Ambondromifehy , S d’Anivorano-Nord , VI.1970, Capuron s.n. ( K [ K000805469 ], P [ P02222313 ]) ; Andrahanjo, cTOn Ambohimbajo , 16.V.1957, Christophe 8980 ( P [ P02608860 ]) ; montagne des Français , V.1924, Perrier de la Bâthie 16211 ( P [ P02324470 ]) ; Manongarivo RS , bassin de l’Ankazomena , 13°56'S 48°27 'E, 2.VI.2000, Wohlhauser & Andriamalaza 60285 ( K [ K000805467 ], P [ P04430800 ]) .

Figures

Fig. 8. – Distribution maps. A. Panicum cupressifolium A. Camus (stars), P. danguyi A. Camus (triangles), P. dregeanum Nees (circles) and P. flacourtii A. Camus (squares); B. Panicum humbertii A. Camus (stars), P. humile Nees ex Steud. (triangles), P. ibitense A. Camus (circles) and P. inconspicuum Voronts. (squares).