Taxonomy

Pilularia globulifera L., Pillwort, has no synonyms and is readily distinguished from all other British species.

Identification

It is a tiny fern, about 8cm tall, which is easily recognised by the characteristically unfurling leaves and the large (3mm), round sporocarps, if present (Page 1997, Stace 1997). The only similar fern in Europe is P. minuta, which occurs in the western Mediterranean but not in Britain (Tutin et al. 1993). It is perhaps most easily confused with seedlings of Juncus, or submerged Juncus bulbosus plants; specimens should always be collected or photographs taken if a new site is found.

Status

Pillwort is considered to be Nationally Scarce and is shown on maps to be declining slightly. It has been introduced or reintroduced to numerous sites by conservationists, sometimes with some success. At Dowrog Common was reintroduced in about 1980 and has flourished since then (Dyfed Wildlife Trust records). Scottish Natural Heritage introduced it to the island of Rum in 1996 and 1997, and it has survived there for some years (David Pearman, pers. comm.).

Distribution

Endemic to Europe, and said to be declining throughout its range on the continent (Page 1997).

In Britain it is widespread but restricted to suitable habitats, which are limited to about ten clusters around the country. It has largely gone from the lowland lakes in Norfolk, the Meres & Mosses, and the Scottish lowlands.

Ecology

Jermy, in Stewart, Pearman & Preston (1994) gives a detailed account of its habitat in shallow water on pond margins, in poached wet grassland and even, occasionally, in mires.

Populations can vary greatly from year to year, often responding quickly to low water levels leaving exposed bare substrate. Jermy (ibid.) reports that spores can develop through the gametophyte stage to produce new sporophytes in just 17 days, which makes it an opportunistic coloniser. He questions whether the sporocarps remain dormant for long periods, or whether new habitat is colonised by fresh spores from nearby populations.

In the north of Scotland it seems to occupy quite a different niche. Most of the records are for the sides of rivers and lakes where, perhaps, the scouring effect of running water creates the open conditions it requires.