This section is from the book "British Wild Flowers - In Their Natural Haunts Vol5-6", by A. R. Horwood. Also available from Amazon: A British Wild Flowers In Their Natural Haunts.
The habitat of this plant is marshes. Marsh Arrow-grass has the grass habit. The plant is stoloniferous. The stem is swollen below. The leaves are slender, half-round in section, limp, faintly channelled above. The scape is slender. The flowers are in a long raceme, lengthening after flowering, on short stalks. The perianth is purple-bordered. The anthers are purple. The fruit is club-shaped, linear, angular, appressed to the scape, the 3 combined carpels attached to the 3-sided axis by a point, round at the back, slender, long, narrow below, or arrow-shaped in fruit (hence Triglochin). The plant is 6-12 in. high, flowering between June and August, and is a herbaceous perennial.
The habitat of this plant is bogs, sphagnum bogs, and marshes. The plant has the grass habit. The rootstock is long, creeping, slender, clothed with the old leaf-stalks. The leaves are half-round in section, in two rows, few, alternate, blunt, with a small pore on the upper side of the tip. The sheaths are swollen, brown. The flowers are few, 5, greenish, borne on a stout, curved scape, in a terminal, loose raceme, the flower-stalks lengthening in fruit. The perianth-segments are linear to oblong. There are 3 capsules, which are swollen, and large in proportion to the size of the plant. The plant is 6-8 in. high, flowering in July and August, and is a herbaceous perennial.