Cyperus engelmannii (Engelmann's flatsedge, "Hosomikingayatsuri")

Japanese name: ホソミキンガヤツリ （細実金蚊帳吊）
Scientific name: Cyperus engelmannii

[Overview]
An annual 20–100 cm tall, found in damp places such as wetlands and the banks between paddy fields.
The stems grow in tufts and are triangular in cross section.
The leaves are attached near the base, linear, 0.5–0.8 cm wide, and the sheath at the base is tinged red.
At the stem tip it produces 7–15 branches bearing spikelets, and 3–8 long leaf-like bracts are attached at the base.
The spikelets are golden yellow, linear, about 1–3 cm long and 0.1 cm wide, and are attached in large numbers, somewhat obliquely, to the axis of the inflorescence.
The scales are arranged in two rows, oblong and about 3 mm long, slightly blunt at the tip, with a green midrib and a rounded back.
The fruit is narrowly obovate to oblong, 1.5–1.8 mm long and 0.5 mm wide, with 3 ridges.
By the time the fruit ripens, the scales separate from one another, and the axis of the spikelet becomes a cork-like wing that encloses the fruit.
There is a joint between the base of the spikelet and each scale, and when the fruit ripens the spikelet breaks apart and falls.

[History]
It was collected in Tokyo and Chiba in the mid-1980s, and has been confirmed as naturalized from the Kanto region westward.

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