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Kali tragus, the Russian thistle Leaves of a mature plant coming into flower, each leaf with one flower and two bracts in its axil. Salsola tragus is an annual forb.In habit, the young plant is erect, but it grows into a rounded clump of branched, tangled stems, each one up to about a metre long.
Centaurea solstitialis, the yellow star-thistle, is a species of thorny plant in the genus Centaurea, which is part of the family Asteraceae. A winter annual, it is native to the Mediterranean Basin region and invasive in many other places. It is also known as golden starthistle, yellow cockspur and St. Barnaby's thistle (or Barnaby thistle). [1]
Individual plants reach 1–1.5 m (3.3–4.9 ft) tall, have once or twice pinnatified leaves (see image of leaf), and abundant spines on the stems and leaves. It produces yellow flowers with pentagonal corollas 2–3.5 cm (0.79–1.38 in) in diameter and weakly bilaterally symmetric (see flower-closeup image). [ 6 ]
The flowers are usually dioecious, but not invariably so, with some plants bearing hermaphrodite flowers. [20] The seeds are 4–5 mm long, with a feathery pappus which assists in wind dispersal. [ 26 ] [ 27 ] [ 28 ] One to 5 flower heads occur per branch, with plants in very favourable conditions producing up to 100 heads per shoot. [ 14 ]
Some larvae tunnel through the upper stem instead of chambering in a flower head; this can also be destructive to the plant. Adults do some damage as well when they feed on the foliage. Thistles which reproduce only via seed, such as musk thistle , are controlled well by this weevil and its seed head destroying larvae.
Thomas Nuttall (1786-1859) described var. megacanthum as "one of the most terribly armed plants in the genus." [ 8 ] [ 9 ] Cirsium horridulum is a biennial herb up to 250 centimetres (100 in) tall, with a large taproot and fleshy side roots that sometimes sprout new shoots.