This section is from the book "British Wild Flowers - In Their Natural Haunts Vol2-4", by A. R. Horwood. Also available from Amazon: A British Wild Flowers In Their Natural Haunts.
This ancient species is found in Interglacial beds in Hants and Sussex, Late Glacial, Neolithic beds at Edinburgh, Roman beds at Silchester. It is found to-day in Arctic and Temperate Europe, N. and W. Asia, and has been introduced into North America. It is found in every county except Main Argyle, as far north as the Shet-lands; up to 1800 ft. in Northumberland. It grows in Ireland and the Channel Islands.
There is scarcely a gateway in close proximity to a barn or outhouse, in a field, or attached to a farmhouse or ordinary dwelling, around which Knotgrass does not form a wide uniform carpet many yards in extent. It is abundant wherever agricultural operations are conducted, and also on waste ground.
This plant is widely spreading, trailing, twining, with numerous, branched, slender, finely-furrowed, smooth, jointed stems, with swollen joints. The leaves are variable, oval, lance-shaped, linear, alternate, issuing from the sheaths of the stipules or ocreae, which are membranous, white, shining, torn, red at the base, and 2 - lobed. The young leaves are erect at night. The flowers are apet-alous, without a corolla, in the axils of the stipules, in spikes which are long, loose, interrupted and leafy below the flower-stalks, jointed above, white, pink, red, or green, the calyx hollow, the lower green, half-spreading, the upper white or coloured. The 8 anthers are yellow, the fruit is brown, triangu-lar, finely furrowed. There are 3 styles. The plant is seldom more than 3-6 in. high. It flowers in April up till October. The plant is perennial, and propagated by seed.
The flowers are small and inconspicuous, the plant being usually prostrate. There is little or no honey or scent, so that insects are few. The flowers are hardly 2 1/2 mm. long, solitary, scentless, and self-pollination is effective. The floral mechanism is as in Fagopyrum. The 5 segments of the perianth with the function of the corolla serve as a calyx, the lower part being green, the extremities white or red, and they act as a corolla to make the flower conspicuous. The 5 stamens alternate with the perianth segments, and bend outwards, and three others bend inwards to the centre till the anthers stand just above the stigmas and at the same level, and are thickened at the base to contain honey; but the flower only offers pollen. The flower is hermaphrodite and homogamous, and visitors by the position of anthers and stamens self-pollinate the flower as well as cross-pollinate it. It is visited by Ascia podagric a, Syritta pipiens, Melithreptus. It has cleistogamic flowers under the ochreae, as well as subterranean cleistogamic flowers.
Photo. J. H. Crabtree - Knotgrass (Polygonum Aviculare, L.)
The fruit is triquetrous and enclosed in the perianth, which may partly aid in its dispersal by the wind.
Knotgrass is a sand-loving plant addicted to sand soil.
This plant is attacked by 2 rusts, Uromyces polygoni, Ustilago utriculosa, in the flowers, and galled by Asychna aeratella. Several beetles frequent it - Gastroidea polygoni, Spercheus emarginatus, Apion difforme, Gastrophysa polygoni; 3 moths, Brown Russet (Russina tene-brosa), Blood-vein (Bradyepetes amataria), and Asychna aeratella; and a Homopterous insect, Aphalara calthae.
Polygonum, Dioscorides, is from the Greek polus, many, gonu, knee, from the numerous nodes, and aviculare, from Latin avis, bird, because it is used for bird-seed.
The plant is called Allseed, Armstrong, Beggar-weed, Bird's Knotgrass, Bird's Tongue, Black Strap, Bloodwort, Centinode, Cow-grass, Crab-grass, Crab-weed, Cumberfield, Doorweed, Finzach, Iron, Knot, Pig, Swine's, and Wiregrass, Hogweed, Knotgrass, Knotwort, Mantie, Nine-joints, Ninety-knot, Pig-rush, Pig-weed, Pink-weed, Red Legs, Redweed, Red Robin, Sparrow-tongue, Stone-weed, Swine-carse, Swine's Skir, Tackers-grass, Surface Twitch, Way Grass, Wireweed.
From the difficulty of pulling it up it is called Armstrong; Swine's Grass because, as Coles says, "Swine delight to feed thereon"; and "it is given to swine with good successe when they are sicke, and will not eat their meate. Whereupon the country people do call it Swine's Grasse and Swine's Skir", according to Gerarde. It is called Nine-joints because "of its great number of joynts", according to Coles. By Doctrine of Signatures it was called Knotgrass from some property it was supposed to have of stopping the growth of children. So Shakespeare in Midsummer-Night's Dream refers to it as the "hindering- Knotgrass", and Beaumont and Fletcher also, in Coxcomb, Act II, Sc. 2: " We want a boy extremely for this function kept under for a year with milk and Knotgrass".
The seeds are used as bird-seed. The plant is astringent, and has been used in dysentery, haemorrhage, etc.
Essential Specific Characters:267. Polygonum aviculare, L. - Stem procumbent, branched, leaves narrow, oblong, flowers in axillary clusters, stipules (ocreae) fringed.