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.
Knapweed is well distributed at the present day throughout Europe. In N. America it is an introduction. No traces of it occur in any ancient deposit, in spite of its being so common to-day.
It is found in every district in Great Britain, and ascends to 1600 ft. in Northumberland.
No meadow would be complete without a sprinkling of the dark heads of Knapweed in summer. It is a plant that grows along every wayside, and is found on hills and dry pastures in great abundance, being addicted to both wet and dry ground.
The wiry hard stems of Knapweed are a familiar sight in a hay-field scattered here and there, and when in flower the plant is easily recognized. The stems are very erect and either simple or branched, furrowed, the branches bearing a single head of flowers.
In the autumn the prevalent habit is characterized by the half-erect branches. The lower leaves are angular, divided, with the lobes enlarged upwards, on long stalks, toothed, and the upper ones are without stalks, egg-shaped, entire.
The flowers or "hard heads" are purple with bractlike scales fringed with hairs at the margin, brownish-black, and egg-shaped, narrowly elliptical. The flowers differ, in some instances possessing a ray or not. The hair or pappus is short, or wanting. The fruit is grey, oblong, and downy.
The plant grows to the height of 1 - 2 ft. It is usually in flower in June, continuing late in the autumn, and even when frosts are frequent. It is perennial, and may be propagated by seeds.
The marginal florets are like those in the centre, but are some-times enlarged and neuter as in Centaurea Cyanus. The corolla is tubular, and enlarged above, making" it accessible to many insects. The flowerheads are purple and conspicuous. The central florets are bisexual, the filaments glandular, and the anthers have an appendage at the farther extremity.
Photo. Flatters & Garnett
The fruits have short hairs which aid in their dispersal by the wind like other Composites.
Knapweed is a clay plant, growing- on clay soil, or sandy loam, and is common on Triassic and Liassic formations, Boulder clay, etc.
A search over the leaves will reveal two kinds of cluster cup, Puccinia arenariicola and P. centanreae. A gall, Chiophora solstitialis, infests it; two beetles, Sphaeroderma cardui, Cassida vibex; the moths Parasia metznerinella, Coleophora conspiciella, C. alcyonipennella, Common Heath (Fidonia atomaria), Lime Speck (Eupithecia centau-reata, Depressaria liturella, D. arenella; a Heteropterous insect, Onco-tylus viridiflavus; and the flies Urellis elata, U. 4-fasciata, Trypeta jaceae.
Centaurea, Pliny, is from Centaur, which is fabled to have had its foot cured by the plant. The specific name, nigra, is Latin for black. Knapweed is the same as Knobweed, from its knob-like head. So common a flower is certain to be known by a variety of names, such as Bachelor's Buttons, Ballweed, Belweed, Black Soap, Blue Tops, Boleweed, Bolwes, Bowweed, Bowwood, Bullweed, Bunds, Bundweed, Buttonweed, Centaury, Great or More Centaury, Churl's-head, Clobweed, Club-weed, Cnop-wort, Cockheads, Codweed, Crop-weed, Darbottle, Drumstick, Hardhead, Hardhead Horse, Hard-iron, Harebottle, Harsh-weed, Horse Hardhead, Horse Knobs, Horse Knops, Horse Knot, Horse-snap, Hurt-sickle, Hyrnehard, Iron-heads, Iron-weed, Knapweed, Knobweed, Knop-weed, Knot-grass, Knotweed, Lady's Cushion, Logger-heads, Matfellon, Shaving-brush, Sweeps, Tarbottle, Tassel, Yronhard.
Knapweed was called Bullweed because cattle were said to be fond of it, and Churl's Head from its rough hairy head, Codweed because the head is like a pudding bag. Drumstick is applied because the head is like a drumstick, Horseknot from being used in divination, and Knobweed from the round head.
In Chaucer's day it was called Matfellon, and it was one of the ingredients of the ointment "Save" for wounds and the pestilence. It was also used to promote appetite, with pepper.
Essential Specific Characters: 174. Centaurea nigra, L. - Stem erect, rigid, furrowed, radical leaves lyrate, lobed, upper lanceolate, flowerheads purple, with ray or not, phyllaries with black fringe, pappus tufted.