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 lakesides, bogs and ditches, turfy bogs. The plant has the rosette habit. The stems may be erect or creeping, tufted. The leaves are all radical, erect, linear to lance-shaped, acute, long-stalked, the blade 3-ribbed. The first leaves are submerged, floating, transparent. The flowers are pale - purple, in umbels or whorls, the flower-stalks or scapes bearing simple branches. The carpels form a head, and are 4-5-ribbed, swollen, angular, acute, egg - shaped, blunt - pointed. The styles are terminal. The plant is 6-18 in. high, flowering between June and August, and is a herbaceous perennial.