Setaria pumila (Poir.) Roem. & Schult.
yellow bristle grass
Loosely to densely tufted, erect annuals, 25-35-(85) cm, green or yellow-green, often purplish near base. Leaf-sheath strongly compressed, firm, but ± membranous towards margins, glabrous, flattened and keeled. Ligule ciliate, hairs 0.5-1.5 mm. Leaf-blade (3)-5-15-(23) cm × (2.5)-3-5-(6) mm, flat, soft, linear or linear-lanceolate, distinctly twisted, tapering above, glabrous, or adaxially slightly scabrid and with long, fine, soft, tubercle-based hairs towards base; margins very minutely scabrid, tip slender, acuminate. Culm 15-65-(75) cm, compressed, erect or geniculate-ascending, rooting at lower nodes, internodes scabrid, to ± densely minutely pubescent below panicle. Panicle (1)-2.5-10 cm × 5-15 mm, cylindric, dense-flowered; rachis densely pubescent, with numerous, very short, close-set, pubescent branches, each usually bearing a single spikelet, sometimes with 1-2 abortive spikelets, subtended by 5-10 greenish to golden brown, antrorsely scabrid, unequal bristles (5-8.5 mm). Spikelets 2.5-3.5 mm, pale green at first, later purple, falling entire at maturity. Lower glume 0.8-1.7 mm, ovate, acute or apiculate, 3-nerved, upper 1.7-2.3 mm, subacute, 5-nerved, ovate-orbicular, convex. Lower floret usually Ø, rarely ♂: lemma 5-nerved, acute; palea ≈ lemma, hyaline; anthers 0.9-1.4 mm, or 0. Upper floret ⚥: lemma = spikelet, crustaceous, prominently transversely rugose, becoming yellowish or brownish, broadly naviculate, very convex, sometimes apiculate; palea of same texture but ≤ lemma, keels rounded and thickened, minutely hairy towards apex, otherwise glabrous; anthers 0.9-1.6 mm; caryopsis c. 1.5-2 mm.
N.: North and South Auckland, Gisborne (Airport), Hawkes Bay (Wairoa), Taranaki (New Plymouth, Patea), Wairarapa (Carterton); S.: Nelson, Marlborough, Canterbury (near Christchurch, Ashburton); K. Open pasture, waste places, roadsides, footpaths, old gardens, cultivated ground.
Naturalised from southern Europe.
Setaria pumila resembles S. gracilis in the number of bristles subtending the spikelet, but S. pumila is an annual whereas S. gracilis is a perennial with a short, wiry, twisted rhizome. Spikelets of S. pumila are often larger than those of S. gracilis.
A. E. Esler (in litt.) noted a red form of S. pumila growing at Pukekohe. Plants had mainly erect tillers compared to the mainly oblique tillers of the usual green form; ligule c. 2 mm; leaf-blade with a conspicuous red patch and smooth adaxially; awns < those in green plants.
Setaria pumila has also been known in N.Z. as S. glauca and S. lutescens. The long discussion over the correct name of yellow bristle grass seems, "to be resolved in favour of S. pumila (Poir.) Roem. & Schult. - the familiar S. glauca (L.) P. Beauv. being regarded as a species of Pennisetum" [Clayton, W. D. Kew Bull. 33: 501-508 (1978)].
