I. Pseudacorus: aquatic; stem two feet high; leaves sword-shaped, the lower ones longer, stiff and erect, glaucous-green; flowers 2-3, large, erect, bright yellow, the outer perianth-segments spreading, broadly ovate, clawed, the inner oblong, erect. - Yellow Flag. - Wet meadows and watercourses. Fl. June and July.

I. foetidissima: leaves narrow, sword-shaped, deep green, having a peculiar smell when bruised; flowers smaller, several together, dull livid purple, rarely pale-yellowish white, the outer perianth-segments narrow-ovate. - Gladdon, or Roast-beef-plant. - Woods and shady places. - Fl. May to July. The smell of this plant is sometimes compared to that of roast beef, and Hooker and Arnott have a curious remark, that in Devonshire it is so frequent that one can hardly avoid walking on it when herborizing, and being annoyed by the smell.