Flora of New Zealand Series

wireweed

Glabrous annual, sometimes biennial, mostly prostrate or decumbent, sometimes spreading; stems numerous, slender, wiry, to c. 1 m long, often forming large, flat mats to c. 1.5 m diam.; taproot fairly stout. Lvs of young and main stems often twice as large as those of branches, subsessile or with petiole to 1 cm long. Lamina (3)-10-40 × (0.5)-3-15 mm, lanceolate to elliptic or ovate, rarely obovate or linear, green or glaucescent, sometimes purplish, entire; base cuneate or rounded; apex acute or subacute; branch lvs sometimes < 5 mm long. Ochreae initially 2-5 mm long, longer in young plants, silvery-hyaline, ± acute, becoming brown, soon lacerate, often enclosing petiole. Fls 1-6 in fascicles in the axils of lvs, extending almost to stem bases; pedicels enclosed by ochreae. Perianth 2-3 mm long at anthesis, usually united for 1/4-⅓ length; segments strongly imbricate, rarely only slightly imbricate, ± oblong, glabrous; margins and apex white, pale pink, or rose, often variously coloured on the same plant, accrescent. Nut 2-3 mm long, ovoid to almost biconvex, dark reddish brown, ± shining, finely striate or granular, regularly trigonous or sometimes 1 side wider or narrower than others, enclosed in perianth or with apex protruding.

N.; S.: abundant to c. 700 m; St.: rare; K. (casual), Ch., C. (casual).

Europe 1853

Cultivated ground, waste places, railway tracks, roadsides and other modified habitats, also poor and open pastures and riverbeds.

FL Nov-Jun.

Wireweed is a characteristic summer annual and is also notable for variation in size and habit, lf form and fl. colour. Until recently there has been little or no subdivision of this polymorphic group in N.Z., but now the general practice in Europe and elsewhere is to split P. aviculare into several spp.; of these P. arenastrum can be distinguished fairly easily in N.Z., but none of the others can be clearly separated or do not occur here. Some specimens approach the European P. rurivagum Boreau; such plants (e.g., CHR 295764, Point Tryphena, North Id, Kirk) are smaller and more slender than is usual for P. aviculare, the lvs are linear to narrow-lanceolate, mostly < 1 cm long, and ± dimorphic, there are 1-3 fls per node, the perianth lobes are not or only slightly imbricate, and the apex of the nut is often exserted. All these features are said to be characteristic of P. rurivagum. But other N.Z. specimens show only some of these features; thus P. rurivagum cannot be clearly distinguished and is not accepted here.