British ferns (Filicopsida)
Small Adders Tongue.
Sporophyte. The rhizomes subterranean, very short, erect (with new plants arising from adventitious buds on the roots); naked. Plants with no clear distinction into fertile and sterile leaves (but hard to interpret as such: usually bearing only a single leaf comprising two components, the lower sterile and laminate, the upper a fertile, non-laminate spike - see below), or bearing markedly different fertile and sterile leaves (the fertile leaf sometimes accompanied by one or two sterile blades). Plants having sterile blades mostly 3–3.5 cm long, the sporangia 6–14 on either side of the spike.
Leaves to (2–)3.5(–10) cm long; not circinnate; compound (when fertile, see above, though the green blade is simple), or simple and compound (when sterile blades occur). The fertile leaves having the appearance of a stem with a terminal fertile portion and a single lateral leaf, but actually comprising two pinnae, the upper fertile, stalked and non-laminate, the lower sterile, sessile, and laminate. The sterile green blades (1.5–)3–3.5 cm long (basally strongly narrowed to more or less stalked); simple and entire; green blades with free vein endings within the network. The fertile spikes 0.8–2 cm long; unbranched. The petioles vascularised via a single strand (this representing a single leaf trace arising from the lower angle of the leaf gap). The venation of the lamina reticulate (i.e., in the sterile blade, although it exhibits minute free vein endings inside the network).
Eusporangiate. The sporangia all alike, relatively massive, sessile and coalescing in two rows on the spikelike fertile component of the leaf (6–14 on either side of the spike); marginal (in origin); exposed; not aggregated into sori. The sporangial wall of several cell layers; without an annulus. The sporangia dehiscing via median slits transverse to the axis bearing them (i.e., transversely to the axis of the spike). The mature spores trilete.
Prothallus. Prothalli non-green, subterranean, mycorrhizal.
Distribution and habitat. In barish or grassy places on sandy or peaty damp soils near the sea. Scattered around coasts of the British Isles, not in eastern Ireland, eastern Scotland or eastern England except Cheviot (Stace, 1997).
Vice-county records. Britain: West Cornwall, South Devon, North Devon, South Somerset, Dorset, South Hampshire, Merionethshire, Caernarvonshire, Anglesey, Cumberland, South Aberdeenshire, Banffshire, Moray, South Ebudes, Mid Ebudes, North Ebudes, West Sutherland, Caithness, Outer Hebrides, Orkney islands, Shetland, Channel Islands. Ireland: South Kerry, North Kerry, Waterford, West Galway, West Mayo, Sligo, East Donegal, West Donegal.
Classification. Family Ophioglossaceae (C.T.W.); Ophioglossaceae (Swale and Hassler); Ophioglossaceae (Stace). Order Psilotales (Swale and Hassler).
O. azoricum C. Presl may be a hybrid, representing O. vulgatum x O. lusitanicum.
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’.