Pillwort

Pillwort has slender, cylindrical, rush-like fronds up to 8 cm (3.1 in) tall that are shaped like croziers as they unfurl. It has a pea-shaped, 4-chambered sporocarp about 3 mm (0.1 in) in diameter, each chamber formed from a modified leaf and containing several sori bearing both megasporangia and microsporangia. The species is thus heterosporous.

Pillwort grows on silt and mud at the margins of lakes, ponds and other watercourses that are submerged for at least part of the year. Some of the plants growing in association with this species in the UK include water celery (Apium inundatum), marsh pennywort (Hydrocotyle vulgaris) and lesser spearwort (Ranunculus flammula). In its habitat in shallow water on pond margins or in poached wet grassland, it seems to grow well in bare locations where it faces little competition. Populations vary greatly from year to year; it sometimes "disappears" from a site only to recur there many years later, and cleaning out a ditch may stimulate it to reappear.

Pillwort can be grown in a "bog garden" or as a marginal aquatic in a garden pond.

== References ==