British ferns (Filicopsida)
Sporophyte. The rhizomes long, slender (to 50 cm); creeping; hairy. Plants bearing markedly different fertile and sterile leaves, or with no clear distinction into fertile and sterile leaves (the 2–4 mm long, shortly-stalked, hard, bean-like sporocarps enclosing the sporangia are borne in the axils or at the bases of the subulate green leaves, and may be interpreted either as highly modified leaves, or as fertile pinnae).
Leaves distributed along the rhizomes (but often tufted on short axillary branches); to the conspicuous, green, vegetative ones, as distinct from the tiny sporocarps, 3–8(–15) cm long; circinnate; subulate; at least ostensibly, simple; entire.
Heterosporous. The sporangia in tiny, 4-compartmented, hairy, pill-like sporocarps at the bases of the subulate green leaves, the compartments each containing one sorus which splits longitudinally at maturity to release the sporangia in a mass of mucilage (the one-spored megasporangia borne below the many-spored microsporangia in the same sorus); unconventionally aggregated in sori (see above). The sori elongated; remaining discrete at maturity. The sporangial wall without an annulus.
Prothallus. Prothalli endosporic and reduced (projecting from the split spore walls).
Distribution and habitat. Aquatic to helophytic; when submerged, rooted in the submerged substrate. On silty mud by lakes, ponds and reservoirs, submerged for part of the year. Throughout the British Isles, formerly much commoner, now frequent only in central western Ireland, central southern England and parts of Wales.
Vice-county records. Britain: West Cornwall, East Cornwall, South Devon, South Somerset, North Somerset, South Wiltshire, Dorset, Isle of Wight, South Hampshire, North Hampshire, West Sussex, East Sussex, Surrey, South Essex, Hertfordshire, Middlesex, Berkshire, Oxfordshire, East Suffolk, East Norfolk, West Norfolk, Cambridgeshire, Huntingdonshire, Northamptonshire, Herefordshire, Warwickshire, Staffordshire, Shropshire, Glamorgan, Breconshire, Radnorshire, Pembrokeshire, Cardiganshire, Montgomeryshire, Merionethshire, Caernarvonshire, Flintshire, Anglesey, South Lincolnshire, North Lincolnshire, Leicestershire, Cheshire, South Lancashire, West Lancashire, South-east Yorkshire, North-east Yorkshire, South-west Yorkshire, Mid-west Yorkshire, North-west Yorkshire, Durham, South Northumberland, Westmorland, Cumberland, Isle of Man, Dumfriesshire, Kirkcudbrightshire, Wigtownshire, Ayrshire, Lanarkshire, Midlothian, West Lothian, Fifeshire, Stirlingshire, West Perthshire, Mid Perthshire, East Perthshire, Angus, Kincardineshire, South Aberdeenshire, Banffshire, Moray, East Inverness-shire, Argyll Main, Dunbartonshire, Kintyre, South Ebudes, Mid Ebudes, North Ebudes, East Ross, East Sutherland, West Sutherland, Outer Hebrides, Channel Islands. Ireland: South Kerry, North Kerry, West Galway, East Mayo, West Mayo, West Donegal, Tyrone, Armagh, Down, Antrim, Londonderry.
Classification. Family Marsileaceae (C.T.W.); Marsileaceae (Swale and Hassler); Marsiliaceae (Stace). Order Marsileales (Swale and Hassler).
Illustrations. • P. globulifera: Eng. Bot. 1825 (1886). • P. globulifera: Sowerby and Johnson (1859). • P.: details (Goebel).
To view the illustrations with detailed captions, go to the interactive key. This also offers full and partial descriptions, diagnostic descriptions, differences and similarities between taxa, lists of taxa exhibiting or lacking specified attributes, and distributions of character states within any set of taxa.
Cite this publication as: ‘Watson, L., and Dallwitz, M.J. 2004 onwards. British ferns (Filicopsida). Version: 4th January 2012. http://delta-intkey.com’.