spikes or racemes, often forming terminal panicles. Perianth inferior, persistent; segments 3–6, free or connate at the base, imbricate. Stamens 5–9, rarely more or less, hypogynous or perigynous; filaments capillary or subulate, free or connate at the base; anthers 2-celled. Ovary superior, compressed or 3-gonous; styles 1–3; ovule solitary, basal, orthotropous. Fruit a small hard indehiscent trigonous or compressed nut, usually enclosed in the persistent perianth. Seed erect, testa membranous; albumen copious, farinaceous; embryo variable in position, radicle superior.
A rather large order, spread over the whole world, but most abundant in the north temperate zone. Genera 30; species over 600. The roots of many species are nauseous and purgative, the medicinal rhubarb being a well-known instance. On the other hand, the stems and leaves are frequently acid and refreshing, as the garden-rhubarb and the common sorrel. Buckwheat (Fagopyrum) is the only edible plant of any consequence. Of the 3 New Zealand genera, Muehlenbeckia extends to Australia and South America; the remaining 2 are widely distributed in both hemispheres.
| Flowers hermaphrodite. Perianth-segments 5, not succulent in fruit | 1. Polygonum. |
| Flowers hermaphrodite. Perianth-segments 6, the 3 inner enlarging and closing over the fruit, not succulent | 2. Rumex. |
| Flowers unisexual. Perianth-segments 5, enlarged and succulent in fruit | 3. Muehlenbeckia. |
1. POLYGONUM, Linn.
Herbs, rarely shrubby at the base. Leaves alternate; stipules membranous, usually tubular and closely sheathing the stem. Flowers small, hermaphrodite, clustered; clusters either axillary or in racemes or spikes or panicles; bracts and bracteoles membranous, ochreate; pedicels usually jointed. Perianth 5-partite, green or coloured; segments equal or the 2 or 3 outer ones the largest. Stamens 5–8. Ovary compressed or 3-gonous; styles 2 or 3, free or connate at the base; stigmas usually capitellate. Nuts compressed or 3-gonous, included in the persistent perianth. Seed albuminous; embryo excentric or lateral; radicle long, superior.
A large and almost cosmopolitan genus, including over 150 species. The three found in New Zealand are all widely distributed.
| * Stems prostrate. Flowers in axillary clusters. | |
| Stems long, wiry, sparingly branched. Perianth ⅛ in. long. Nut minutely striate or punctate | 1. P. aviculare. |
| Stems short, compactly branched. Perianth 112 in. long. Nut smooth and polished | 2. P. plebeium. |
| colspan=2 | ** Stems erect or ascending above. Flowers in slender terminal spikes. |
| Leaves 2–5 in., lanceolate. Stipules ciliate and pilose. Spikes very slender, 1–2 in. long | 3. P. serrulatum. |
For references to several introduced species of Polygonum, see the list of naturalised plants appended to this work.
