Polygonum L.
Annual or perennial herbs, occasionally small shrubs, sometimes aquatic or ± scrambling; stems usually solid, with nodes usually obviously jointed and often swollen. Lvs cauline, very variable but usually considerably longer than wide, usually entire; ochreae well-developed, scarious. Infl. axillary or terminal, usually a fascicle, spiciform raceme, capitate head, or diffuse panicle; fls generally ⚥, sometimes unisexual (plants monoecious or dioecious). Pedicels generally jointed. Perianth segments (4)-5-(6), persistent but usually not markedly accrescent, free or united at base, equal or nearly so, white, pink to crimson, not keeled. Stamens (3)-5-8-(9). Styles 2-3, variable in length. Fr. a biconvex or trigonous nut, enclosed or slightly exserted from the persistent, spineless perianth valves.
Key
c. 300 spp., temperate regions. Native sp. 1, naturalised 12.
In addition to those described below, there are several other ornamental Polygonum spp. commonly cultivated in N.Z. They are temperate and alpine Himalayan plants which have shown little or no tendency to become wild as yet: the 4 prominent spp. are P. campanulatum Hook. f., with pale pink fls in open panicles and lvs whitish or fawn-tomentose below, P. amplexicaule D. Don, with crimson infls and amplexicaul lvs, P. affine D. Don, with thick, erect, pink or rose infls arising from a prostrate mat, and P. vacciniifolium Wallich, with slender, pink infls and prostrate, trailing stems. The last 3 belong to sect. Bistorta as do most of the spp. grown in rock gardens. Some authorities elevate this and other sections of Polygonum to generic rank leaving only that containing P. aviculare and its relatives in the genus.
