884 THE POLYGONUM FAMILY. [Polygonum. 



ones enlarged. Stamens 8 or sometimes fewer. Styles 3 or 2, some- 

 times united at the base, the stigmas entire. Nut triangular or flattened, 

 enclosed in or surrounded by the persistent perianth. 

 A large genus, widely spread over every part of the globe. 



Stems much branched, wiry, often prostrate. Flowers axillary. 

 Annual. Nuts scarcely above a line long, opaque, dotted, or 



wrinkled 1. P. aviculare. 



Perennial. Nuts about 2 lines long, very smooth and shining 2. P. maritimum. 

 Stems twining. Flowers in loose racemes. 

 Fruiting perianth triangular, scarcely winged . . . 3. P. Convolvulus. 

 Fruiting perianth with 3 white, scarious wings . . . 4. P. dumetorum. 

 Stems usually ascending or erect, or floating. Flowers in 

 terminal spikes. 

 Rootstock perennial. Spikes solitary or rarely 2. 

 Leaves oblong-linear. Spike slender and linear . . . 5. P. viviparum. 

 Leaves ovate or oblong-lanceolate. Spike dense, oblong 

 or cylindrical. 

 Styles 3. Leaves chiefly radical. Stem-leaves few and 



small 6. P. Bistorta. 



Styles 2. Stems floating or ascending, with large, oblong, 



stalked leaves 7. P. amphibium. 



Annuals. Stems branched with several spikes. 

 Spikes dense, seldom above an inch long. 

 Pedicels and perianths quite smooth. Stipules usually 



fringed 8. P. Persicaria. 



Pedicels and perianth rough with glands. Stipules 



usually entire 9. P. lapathifolium. 



Spikes long and slender ; the clusters of flowers, at least 

 the lower ones, distinct. 

 Perianth covered with raised dots. Taste biting . . 10. P. Hydropiper. 

 Perianth without raised dots. Taste not biting . . 11. P. minus. 



The tall Persicaria of our gardens is an east Asiatic Polygonum (P. 

 orientale), and several other Asiatic species have been recently intro- 

 duced into our flower-gardens. The Buckwheat of agriculturists, occa- 

 sionally found on the margins of fields where it had been cultivated, is 

 also an Asiatic plant, included by some in Polygonum (P. Fagopyrum), 

 by others separated into a distinct genus under the name of Fagopyrum. 



1. P. aviculare, Linn. (fig. 869). Knotweed, Knotgrass. — A much 

 branched, wiry annual, prostrate when in the open ground, erect when 

 drawn up amongst corn or grass, often a foot or two long. Stipules 

 white and scarious, becoming ragged at the edges. Leaves narrow- 

 oblong, small, very rarely attaining an inch in length. Flowers small, 

 shortly stalked, in clusters of 2 to 5 in the axils of most of the ' leaves. 

 Styles 3. Fruiting perianths but little more than a line long ; the seg- 

 ments white on the edge, green in the centre. Nuts triangular, seldom 

 exceeding the perianth, not shining, and, when seen through a strong 

 glass, minutely granulated or wrinkled. 



In cultivated and waste places, almost all over the globe, from the 

 tropics to the Arctic regions. Abundant in Britain. Fl. almost the 

 whole season. It varies much in its branches, sometimes very long and 

 slender, with very few distant leaves, sometimes short and densely 

 matted, with the small leaves much crowded. A maritime variety, 

 distinguished as P. littorale, Link., with rather thicker leaves and larger 

 flowers and nuts, has been confounded with P, maritimum, but has not 

 the shining nuts of that species. 



2. P. maritimum, Linn, (fig.- 870). Sea P.— When flowering the 

 first year of its growth, or when luxuriant, this species is distinguished 



