Polygonum aviculare or common knotgrass

Polygonum aviculare or common knotgrass is a plant related to buckwheat and dock. It is also called prostrate knotweed, birdweed, pigweed and lowgrass. It is an annual found in fields and wasteland, with white flowers from June to October. It is widespread across many countries in temperate regions, apparently native to Eurasia and North America, naturalized in temperate parts of the Southern Hemisphere. Common knotgrass is an annual herb with a semi-erect stem that may grow from 10 to 40 cm (4 to 16 in) high. The leaves are hairless and short-stalked. They are longish-elliptical with short stalks and rounded bases; the upper ones are few and are linear and stalkless. The stipules are fused into a stem-enclosing, translucent sheath known as an ochrea that is membranous and silvery. The flowers are regular, green with white or pink margins. Each has five perianth segments, overlapping at the base, five to eight stamens and three fused carpels. The fruit is a dark brown, three-edged nut. The seeds need light to germinate which is why this plant appears in disturbed soil in locations where its seeds may have lain dormant for years. It is a common carrier of the parasitic pathogen powdery mildew, which can give the leaves a whitish appearance. Polygonum aviculare has a wide distribution as an arable weed and plant of fields, shingle, sand, roadsides, yards and waste places. There is much morphological variation among different populations and several different sub-species are recognized: • Polygonum aviculare subsp. aviculare – very widespread • Polygonum aviculare subsp. boreale (Lange) Karlsson – Greenland, Labrador, Newfoundland, Scandinavia • Polygonum aviculare subsp. buxiforme (Small) Costea & Tardif – North America • Polygonum aviculare subsp. depressum (Meisn.) Arcang. – Europe, North America • Polygonum aviculare var. fusco-ochreatum (Kom.) – northeastern China, Russian Far East • Polygonum aviculare subsp. neglectum (Besser) Arcangeli – Europe, North America • Polygonum aviculare subsp. rurivagum (Jord. ex Boreau) Berher – Europe, North America Widespread and common in Great Britain, Ireland, and Scandinavia. Common on roadsides and arable ground in the British Isles. Polygonum aviculare contains the flavonols avicularin, myricitrin and juglanin. The flavanoids astragalin and betmidin, and the lignan aviculin have also been found. The diterpene alkaloid panicudine is another known component. One fossil fruit of Polygonum aviculare has been extracted from borehole samples of the Middle Miocene fresh water deposits in Nowy Sacz Basin, West Carpathians, Poland. It formed a traditional ingredient in porridge consumed by Germanic peoples of western Europe, and has been found in numerous autopsies of peat bodies, including the Tollund Man. In Vietnam, where it is called rau đắng, it is widely used to prepare soup and hot pot, particularly in the southern region. Polygonum aviculare 或commonknotgrass 是一种与荞麦和码头有关的植物。它也被称为匍匐虎杖、鸟草、猪草和低草。它是一年生在田野和荒地上发现的一年生植物，6 月至 10 月开白花。它广泛分布于温带地区的许多国家，显然原产于欧亚大陆和北美，在南半球温带地区归化。 普通虎杖是一年生草本植物，茎半直立，可长至 10 至 40 厘米（4 至 16 英寸）高。叶子无毛且短柄。它们呈长椭圆形，茎短，基部圆形；上面的很少，是线性的和无茎的。托叶融合成一个包围茎的半透明鞘，称为赭石，膜质和银色。花朵规则，绿色，边缘为白色或粉红色。每个有五个花被节，在基部重叠，有五到八个雄蕊和三个融合的心皮。果实是深棕色的三棱坚果。种子需要光照才能发芽，这就是为什么这种植物出现在其种子可能休眠多年的受干扰土壤中的原因。它是寄生病原体白粉病的常见载体，可使叶子呈现发白外观。 何首乌作为可耕地的杂草和植物广泛分布于田地、鹅卵石、沙地、路旁、庭院和荒地。不同种群之间存在很大的形态变异，并识别出几个不同的亚种： • Polygonum aviculare subsp。 aviculare - 非常普遍 • Polygonum aviculare subsp。北欧（朗格）卡尔松 - 格陵兰、拉布拉多、纽芬兰、斯堪的纳维亚 • Polygonum aviculare subsp。 buxiforme (Small) Costea & Tardif - 北美 • Polygonum aviculare subsp。 depressum (Meisn.) Arcang。 - 欧洲、北美 • 何首乌变种。 fusco-ochreatum (Kom.) A.J. Li - 中国东北、俄罗斯远东 • Polygonum aviculare subsp。 ignoreum (Besser) Arcangeli - 欧洲、北美 • Polygonum aviculare subsp。 rurivagum ( Boreau) Berher - 欧洲、北美 在大不列颠、爱尔兰和斯堪的纳维亚广泛流行。 常见于不列颠群岛的路边和耕地。 何首乌含有黄酮醇类的 avicularin、杨梅苷和胡桃苷。还发现了黄酮类化合物黄芪甲苷和 betmidin，以及木脂素鸟苷。二萜生物碱panicudine是另一种已知成分。 已从波兰西喀尔巴阡山脉的新萨克盆地中中新世淡水矿床&#