Paspalum dilatatum Poir.
paspalum
Tufted perennials, sometimes forming dense stands, from short, strong rhizomes to c. 1 cm diam. Leaf-sheath rather stiff, lowermost densely long-hairy, others glabrous. Ligule (2)-3-5 mm, entire, rounded. Leaf-blade (6.5)-12.5-18.5-(25) cm × 5.5-8 mm, rather stiff, flat, glabrous apart from a few long hairs on margins and adaxially near ligule, midrib conspicuous; margins scabrid, narrowed above to acuminate tip. Culm 25-55-(180) cm, ± flattened, to 2.5 mm diam., erect or geniculate-ascending and drooping above, nodes glabrous or the lowermost sparsely pubescent, internodes glabrous. Panicle usually nodding, 8-15 cm, with (2)-3-6 often spreading or drooping, rather distant racemes; rachis slender, flattened. Racemes 4.5-6.5-(11) cm; rachis c. 1 mm wide, narrowly winged, scabrid-margined with numerous white hairs at base, bearing 2 rows of paired, shortly pedicelled spikelets; pedicels scabrid. Spikelets c. 3-3.5 mm, closely imbricate, broadly elliptic-ovate, ciliate, acute, green or purplish. Lower glume 0, upper = spikelet, 5-9-nerved, sparsely hairy, margins ciliate, hairs long, silky. Lower floret: lemma ≈ spikelet, 5-9-nerved, glabrous, or margins sometimes sparsely hairy; palea 0. Upper floret: lemma 2.2-2.5 mm, very broadly elliptic to orbicular, crustaceous, faintly 5-nerved, minutely papillose and longitudinally striate, light cream; palea ≈ lemma, incurved, membranous margins widened at base, forming wings enclosing flower; anthers 0.9-1.3 mm, dark purple; stigmas deep reddish purple; caryopsis c. 1.5 mm.
N.: very common; S.: scattered or locally dense as far south as Taieri R.; K., Ch. Shingly roadsides, waste land, ditch banks, pasture, consolidated sand dunes, also in heated soil at Karapiti, Wairakei.
Naturalised from South America; Brazil to Argentina.
Field, T. R. O. and Forde, M. B. Proc. N.Z. Grasslands Assoc. 51: 47-50 (1990) summarised the spread of paspalum in N.Z. It was abundantly naturalised in North Id by 1935 and reached northern South Id by 1940. By the 1970s it was dominant in pastures in Northland, Coromandel, and Bay of Plenty, and at that time increased spectacularly in southern North Id, and even more markedly since 1985. Substantial populations were also reported in South Canterbury and the Waitaki Valley.
Paspalum dilatatum has been widely sown as a pasture grass. Dormant in winter, it spreads vigorously in late spring and summer. A troublesome weed in lawns and common on shingly roadsides where it can form extensive patches. The flower heads are sometimes sticky through infection with ergot. Paspalum is sometimes sown in swamps and periodically flooded land in the north of North Id. It will live for 5-6 months under water and grows vigorously when the water subsides.
