Flora of New Zealand Series

swamp panicum

Strong, erect, glabrous, light or dull green to purplish annuals, to 120 cm, in diffuse tufts with stems much branched near base. Leaf-sheath submembranous, rounded, somewhat keeled above, glabrous. Ligule a membranous rim c. 0.5 mm, tipped by a ciliate fringe usually c. 1 mm. Leaf-blade 8-20 cm × 4-8 mm, long-tapering, glabrous, firm, midrib prominent; margins sometimes undulate below, tip acuminate. Culm (20)-35-80-(100) cm, terete or compressed, nodes brownish, internodes glabrous. Panicle 15-35 cm, very lax, branches later widely spreading; rachis and branches smooth, branchlets and pedicels finer, minutely scabrid on angles. Spikelets 2.2-2.7 mm, glabrous, ovate-elliptic, obtuse, rather dull. Glumes very unequal; lower 0.6-1 mm, clasping spikelet base, truncate, sometimes with a central subacute tip, upper = spikelet, (7)-9-11-nerved, elliptic, subacute. Lower floret ♂: lemma 9-nerved; palea narrower, narrowly winged above, 2-keeled, keels glabrous; anthers 1-1.8 mm. Upper floret ⚥: lemma 1.8-2 mm, elliptic, subacute, faintly striolate, glabrous, shining, light cream; palea narrower; anthers 1.2-1.6 mm; caryopsis c. 1.5-2 × 1 mm.

N.: North Auckland (Kerikeri), Auckland City, South Auckland (Hamilton); S.: Nelson (Motueka, Moutere, Nelson City), Canterbury (Darfield). Waste land, usually damp places, crop weed.

Naturalised from south-west Africa.

Often forming large spreading patches and becoming troublesome in the Motueka district; spreading especially in irrigated orchards.

Though first collected in 1943 at Auckland (CHR 7765), this sp. was confused for many years with P. dichotomiflorum from which it can be distinguished by the staminate lower florets, obtuse rather than acute-tipped spikelets, the more robust habit and laxer panicle. In Australasia the later synonym P. laevifolium Hack. was applied for a time to swamp panicum, e.g., Vickery, J. W. Fl. N.S.W. No. 19, Gramineae 2: 184 (1975); Edgar, E. and Shand, J. E. N.Z. J. Bot. 25: 343-353 (1987) in a checklist of panicoid grasses.