Setaria gracilis Kunth
knot-root bristle grass
Many-tufted perennials, with mostly inclined culms from an extremely short, slender, knotted, wiry rhizome. Leaf-sheath light green, or distinctly red, or purplish, keeled, submembranous, smooth, sometimes minutely scabrid above; margins glabrous. Ligule ciliate, hairs 0.5-1.2 mm. Collar hairs few, long, tubercle-based. Leaf-blade 5-15 cm × 1.5-6 mm, flat, linear, twisted in upper ½, tapering to scabrid, narrowly acuminate tip, often glaucous, abaxially with obvious midrib, smooth to somewhat scabrid, adaxially scabrid. Culm (2)-20-60 cm, slender, somewhat compressed, internodes very short-pubescent to scabrid just below panicle. Panicle (1.5)-2.5-8.5 cm × 3-8 mm, narrow-cylindric, dense-flowered; rachis densely, softly scabrid-pubescent, with numerous very short branches each bearing a single spikelet subtended by 4-7 unequal, whitish or yellowish, antrorsely scabrid bristles (1.5)-2.5-6 mm. Spikelets 2.2-3 mm, pale green, elliptic, acute. Glumes broadly ovate, obtuse to subacute or apiculate; lower 1-2 mm, 3-nerved, usually < ½ but occasionally to ⅔ length of spikelet, upper 1.5-2.5 mm, 5-nerved, usually ¾ length to occasionally ≈ spikelet. Lower floret: lemma 5-(7)-nerved, ovate; palea = lemma, keels glabrous, rounded. Upper floret: lemma ≈ spikelet, sometimes apiculate, indurated, transversely rugose with close, narrow ridges, convex, greenish at first, later purple-tipped; palea ≈ lemma, somewhat indurated, very finely rugose, keels thickened, smooth except for a few minute prickle-teeth near apex, margins hyaline; anthers 0.6-0.9 mm; caryopsis 1-1.5 mm.
N.: throughout; S.: Nelson, Marlborough (Wairau Valley), Westland (Greymouth). Pasture, roadsides, waste land, gardens, crops (maize, asparagus), often in sandy soil, often in lawns.
Naturalised from North America.
Formerly known as S. geniculata (Poir.) Kunth.
N.Z. plants have bristles 1-2-(3) times the length of the spikelets, in this respect resembling some Australian and South American plants [Vickery, J. W. Fl. N.S.W. No. 19, Gramineae 2: 236 (1975)], but in general bristles in S. gracilis are 3-6 times the length of the spikelet. In N.Z. just as in New South Wales and Victoria (Vickery 1975 op. cit.) some plants are found in which the lower glume is "...up to two thirds and the upper glume c. seven-eighths the length of the spikelet".
Field, T. R. O. and Forde, M. B. Proc. N.Z. Grasslands Assoc. 51: 47-50 (1990) reported that knot-root bristle grass appeared to be particularly abundant in the Bay of Plenty and Manawatu, and had increased in abundance over the last 2-3 years.
Very variable in height, knot-root bristle grass may grow to 60 cm, or in lawns be dwarfed to 2 cm and still produce seeds (A. E. Esler pers. comm.).
