Cirsium vulgare (spear thistle, "Amerikaoniazami")

Japanese name: アメリカオニアザミ
Scientific name: Cirsium vulgare

[Overview]
A annual or biennial 50–150 cm tall, found in fields, pastures, roadsides, riverbanks and wasteland.
The stem is erect and branches in the upper part, and has wings (fins) with sharp spines.
The stem has short woolly hairs.
There are basal leaves and stem leaves.
The basal leaves are deeply pinnately divided and form a rosette; they have usually withered by flowering time.
The stem leaves are alternate and pinnately divided into 3–6 pairs of lobes, with dense spines about 1 mm long on the margin and also on the upper surface.
The underside of the leaves is densely covered with cobwebby hairs.
The bases of the stem leaves clasp the stem.
The stem tip bears 1–3 flower heads in a raceme.
The flower heads are 3–4 cm across and pale reddish purple.
The involucre is ovoid-globose and 3–4 cm wide, and the involucral bracts are recurved or spreading, with sharp spines at the tips.
The fruit is an achene with a white pappus.

[History]
It is widely naturalized in the temperate regions of the world.
It was brought to Japan mixed in with grain and forage imported from North America, and was first confirmed in Hokkaido in the 1960s.
It is found from Hokkaido to Shikoku.

[Notes]
It is designated as an alien species requiring caution under the Invasive Alien Species Act.

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