Soliva sessilis (field burrweed, "Merikentokinso")

Japanese name: メリケントキンソウ
Scientific name: Soliva sessilis

[Overview]
An annual 5–10 cm tall, growing in parks, riverbeds, roadsides and similar places.
The whole plant is covered with many soft hairs.
The stem creeps along the ground, and it repeatedly sends out a branch from the axil of a leaf surrounding a flower head and bears a flower head at its tip.
The leaves are alternate, arranged so as to surround the flower heads, oblong, 1.5–5 cm long, and deeply 2-pinnately divided; there are usually 5–7 leaf segments, and the final segments are about 0.1 cm wide with pointed tips.
It bears yellowish-green flower heads 0.7–1 cm across.
In each flower head, female flowers are on the outside and several bisexual flowers are in the center.
The female flowers have no corolla, only a style, while the bisexual flowers have a yellow corolla with 4 lobes at the tip.
The involucre is hemispherical, and the involucral bracts are membranous and arranged in 2 rows.
The fruit is an achene 0.4 cm long, wider than it is long.
The achene has membranous wings on both sides and a sharp, spine-like style remaining at the tip, giving it a shape compared to a horseshoe crab or a stingray.

[History]
A specimen was collected at Susami, Wakayama, by Soichiro Sakaguchi in 1930, and it was reported by Shiro Kitamura in 1932.
It has become naturalized in western Japan.

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