Paspalum distichum L.
Mercer grass
Perennials, with numerous long-creeping branching stolons to 3 mm diam., rooting at nodes. Leaf-sheath submembranous, glabrous. Ligule 1-1.6 mm, erose, truncate. Collar hairs few, long, tubercle-based. Leaf-blade 2.5-9 cm × 2-8 mm, rather soft, flat, linear-lanceolate, curved at base, abaxially glabrous with obvious midrib, adaxially with scattered, long, fine tubercle-based hairs; margins scabrid, gradually narrowed to acuminate scabrid tip. Culm 7-35-(45) cm, erect or geniculate-ascending, compressed, nodes long-hairy, internodes glabrous. Panicle of (1)-2-(3) erect to spreading racemes, ± digitate at culm apex. Racemes 2-5 cm, sometimes one or both shortly pedunculate; axils with a few long white hairs; rachis 1-2 mm wide, concave, narrowly winged with scabrid margins, bearing 2 rows of single or paired, subsessile or shortly pedicelled spikelets; pedicels scabrid; paired spikelets usually near centre of rachis. Spikelets c. 2.5-3.5 mm, imbricate, elliptic, acute, light green. Lower glume a minute scale rarely to 1 mm, or 0, upper = spikelet, 5-nerved, minutely appressed-puberulent. Lower floret: lemma ≈ upper glume and slightly less membranous, 3-5-nerved, glabrous; palea rarely present, narrow, short, hyaline, 2-keeled. Upper floret: lemma 2-3 mm, faintly 5-nerved, cartilaginous-indurate, finely punctulate-striolate, broad-elliptic, acute, light cream, apex often with tuft of short hairs; palea ≈ lemma, hyaline margins only slightly widened near centre; anthers 1-1.7 mm, dark purple; stigmas dark purple; caryopsis 1.5-2 mm.
N.: throughout; S.: Nelson (Nelson City, Takaka, near Lake Otuhie, Karamea), Canterbury (Christchurch, Lincoln); K. Damp soil at lake edges, sand flats, swampy roadsides, waste ground, also a weed of lawns and cultivated ground - often in fresh, not brackish water.
Naturalised from Europe.
Field, T. R. O. and Forde, M. B. Proc. N.Z. Grasslands Assoc. 51: 47-50 (1990) noted that Mercer grass appeared to be most abundant in Waikato and the Bay of Plenty where it was reported as clogging waterways.
A long controversy concerning the correct application of the name P. distichum L. was ended by the decision of the Committee for Spermatophyta [Taxon 32: 281 (1983)] to retain the name for the sp. growing in freshwater. Because the type specimen was a mixed sheet the name P. distichum was formerly sometimes applied to saltwater paspalum (P. vaginatum), and the name, P. paspalodes (Michx.) Scribn., was applied to the sp. from freshwater. In N.Z. also, Mercer grass was known as P. paspalodes (as in the original spelling), and P. paspaloides.
