Polygonum lapathifolium L.
pale willow weed
Annual; stems ± erect, to 1 m tall, glabrous, green or reddish, often with red spots below the ± swollen nodes; taproot moderately stout. Lvs on main stem similar to those on branches; petioles to 3 cm long. Lamina (2)-3-15-(20) × (0.5)-1-4.5-(7) cm, lanceolate to narrow-ovate, glandular-punctate and glabrate to whitish tomentose below (sometimes hairy only on midrib), often with dark blotch on upper side, entire, ciliate; base ± attenuate; apex obtuse or subacute. Ochreae to 1 cm long, initially green or pinkish, truncate; apex glabrous or ciliolate. Infl. to 4 cm long, erect, dense and cylindric, usually simple and uninterrupted, mostly terminal; pedicels short, obscured by ochrea-like bracts; peduncles sparsely to densely covered with subsessile yellow or cream glands. Perianth c. 2 mm long, sparsely to moderately glandular, somewhat accrescent, usually white, sometimes pink; veins prominent, forked and recurved (anchor-shaped); segments ± elliptic, imbricate. Nut 2.5-3 mm long, usually ± biconvex, occasionally trigonous with rounded edges, dark brown, shining.
N.: scattered localities at least as far north as the Bay of Plenty; S.: locally common in N. Canterbury and Banks Peninsula, scattered localities southwards to Southland.
Temperate N. Hemisphere 1904
Usually waste and arable land, also open disturbed, particularly moist habitats.
FL Nov-Apr.
Possibly poisonous (Connor 1977).
P. lapathifolium is variable in N.Z., especially in respect to size of the vegetative parts and their hairiness. Extreme variants are sometimes regarded as distinct spp. elsewhere, but it is difficult to assign N.Z. specimens to any of them with certainty. Some plants do resemble 2 of these segregates, P. nodosum Pers. and P. tomentosum Schrank, in hairiness and the general appearance of the infl., although there are intermediates in N.Z. as in Europe. Thus, P. lapathifolium has been treated here in the wide sense.
P. lapathifolium is generally much less common than the related P. persicaria. It is often mistaken for P. persicaria, but can be distinguished readily by the glandular peduncles and the forked anchor-shaped perianth veins. Also, seedling lvs of P. lapathifolium are linear-lanceolate whereas those of P. persicaria are ± elliptic.
Healy, A. J., Identification of Weeds and Clovers (1976), recorded an unidentified Polygonum sp. from arable land at Tasman, Nelson. The specimens on which this record was based (CHR 225039, 225040) are most similar to P. lapathifolium, but the hairs on the ochreae resemble those in P. persicaria, and the plants may be hybrids between the two. The plants are robust with scattered antrorse stem hairs; lvs to 20 × 5 cm; ochreae fringed (hairs to 3 mm long) and appressed-strigose; peduncles glandular; perianth deep red and sometimes glandular, with veins anchor-shaped; nut compressed (1 side convex, the other concave) or trigonous. This putative hybrid is apparently fairly widespread now.
