4. Arthraxon castratus (Griffith) V. Narayanaswami ex. Bor, Fl. Assam. 5: 376. 1940.
海南荩草 hai nan jin cao
Andropogon castratus Griffith, Not. Pl. Asiat. 3: 89. 1851; A. pilipes Backer; A. rudis Nees ex Steudel; Arthraxon haina-nensis Keng & S. L. Chen; A. rudis (Nees ex Steudel) Hochstetter.
Perennial. Culms straggling, decumbent, rooting from lower nodes, 60–200 cm long, culm apex pubescent. Leaf sheaths glabrous to densely papillose-hispid; leaf blades lanceolate, 3–11 cm × 7–15 mm, glabrous or sparsely appressed-hispid, base cordate, margins pectinate-setose, apex acuminate; ligule 1–2 mm. Racemes 2–5, 3–7 cm, brownish green or purplish brown, raceme bases slenderly terete, pubescent; rachis internodes 1/3–4/5 length of sessile spikelets, softly pilose, hairs 0.4–1.5 mm. Sessile spikelet 4–8 mm; lower glume broadly lanceolate, leathery, weakly convex, not laterally keeled, margins flat, back asperulous, 7–9-veined, tuberculate-spinulose above middle especially near margins, spicules longer toward apex; upper glume longer than lower glume, broadly leathery, hyaline margins 0.1–0.2 mm, spicules present along upper midline; lemma margins ciliate; upper lemma 2-toothed, teeth ca. 0.4 mm; awn 10–14 mm; palea lanceolate, 1/2 length of lemma. Anthers 3, 2–3.8 mm. Pedicelled spikelet absent; pedicel subulate, 1–3 mm, pilose. Fl. and fr. autumn–winter. 2n = 18, 36.
Dry mountain slopes. Hainan [India, Indonesia, Myanmar, Sri Lanka, Thailand, Vietnam; Australia (Queensland)].
Arthraxon castratus has a distinctive, narrowly elongate, pubescent base to each raceme, and the pubescence is carried down onto the upper part of the culm. The unusually broad, leathery upper glume also imparts a characteristic, broad side view to the spikelets.