Lysimachia fortunei; a species of loosestrife
A perennial herb native to East Asia, found in wetlands. The name literally means 'marsh tiger's tail'.
I found Lysimachia fortunei blooming in the marsh.
Katakana spelling is common for plant names; usually written in kana.
Kanji spelling is rare; the plant is normally written in kana.
The name is a compound of 沼 (numa, 'marsh') and 虎の尾 (toranoo, 'tiger's tail'), referring to the plant's habitat and the shape of its inflorescence.