Cirsium arvense (Canada thistle)
Image credit: Kelly SikkemaIdentification tips
Tip #1: the genus cirisium's name comes from the Greek kirsion,which means swollen vein; an allusion to the use of this plant in antiquity in the treatment of swollen veins. Arvense is from the Latin "arvum", meaning "weave", referencing the growth of the plant in arable soil or in disturbed areas.
Plant shape
2º Identification tip: is a perennial plant and, the roots are sparse and produce new plants, favoring the dissemination of this plant through the pruning, another tip to associate to the name.
Leaves
3º Identification tip: leaves have no stem, with white/yellowish spines scattered across the wavy edges. The lower leaves are larger than the upper ones and more deeply lobed. The upper leaves are narrower and generally more toothed than lobed. The leaves can be a little hairy at the bottom.
Stem
4º Identification tip: The stem is light green, slightly wavy and may have scattered hair, but is usually not prickly.
Flowers
5º Identification tip: flowers are egg to bell shaped, consisting of several overlapping lines of scale-like structures (bracts) with thorns. The flowers are white, purple or pink.
Seeds
6º Identification tip: the seed is brown with a tuft of long whites to transport it to the wind, favoring the spread of the species.
Roots
7º Identification tip: the roots have the capacity to produce new plants, making it difficult to control this species by systemic herbicides, mainly in low doses.
Seedlings - the terror of all
7º Identification tip: cotyledons are oval to oblongs. The central veins on the lower face is bright. The first true leaves are alternated between each other on the stem and the edges are slightly wavy to uneven. The surface of the leaf is covered with rigid hair, but the lower surfaces are usually sparse with soft, coiled hair. Seedlings have undeveloped rosettes.
