British ferns (Filicopsida)
T. radicans auct.
Sporophyte. The rhizomes slender (but over 1 mm in diameter); creeping; hairy.
Leaves persistent for some years; to 7–35(–45) cm long; simple, or compound (usually described as pinnate, but the combination of abnormally thin lamina and narrowly winged rachis and rachillae blurs the conventional definitions); complexly divided (irregularly 2–3 pinnatisect, the pinnules or segments rather irregularly pinnatifid or pinnately lobed, the ultimate lobes small, 1-veined and entire). Pinnae about 7–15 on each side of the leaf. The petioles shorter than the blades to about as long as the blades (about a third to a half of the leaf length, naked, winged above); vascularised via a single strand (representing a single leaf trace). Leaf blades in outline ovate-triangular; very thin and translucent - only one cell thick, lacking stomata. The longest pinnae the lowermost. The venation of the lamina reticulate (the lobes one-veined).
The sporangia marginal (elongated from a basal meristem, and the sporangia maturing in basipetal sequence); aggregated in sori. The sori remaining discrete at maturity; very ambiguously protected by true and false indusia combined (assuming the ostensible indusium reflects this situation). The indusia projecting from the margins of the very thin lamina and enveloping the sori from their bases; by contrast with those of Hymenophyllum, tubular, with the apex of the elongated sporangial receptacle protruding as a bristle when mature. The sporangia developing sequentially within a sorus (becoming elongated via an intercalary meristem); developing basipetally on the elongated receptacle of the gradate sorus, with an oblique annulus.
Prothallus. Prothalli green and filamentous (and mycorhizal?).
Distribution and habitat. In places with very high humidity - on sheltered, damp rock faces, often near waterfalls or at cave entrances. Now very local in western and central England, Wales, SW Scotland, and (mainly) SW Ireland. Formerly commoner, as evidenced by gametophytes surviving in parts of N and SW England and N Wales where sporophytes no longer develop.
Vice-county records. Britain: West Cornwall, East Cornwall, South Devon, North Devon, West Sussex, East Sussex, West Gloucestershire, Monmouthshire, Herefordshire, Staffordshire, Shropshire, Glamorgan, Breconshire, Radnorshire, Carmarthenshire, Pembrokeshire, Cardiganshire, Montgomeryshire, Merionethshire, Caernarvonshire, Anglesey, Derbyshire, South Lancashire, West Lancashire, North-east Yorkshire, South-west Yorkshire, Mid-west Yorkshire, North-west Yorkshire, South Northumberland, Westmorland, Cumberland, Isle of Man, Mid Perthshire, Moray, West Inverness-shire, Argyll Main, Clyde Isles, Kintyre, South Ebudes, Mid Ebudes, North Ebudes, West Ross, East Sutherland, West Sutherland, Caithness. Ireland: South Kerry, North Kerry, West Cork, Mid Cork, East Cork, Waterford, Limerick, North Tipperary, Wexford, Carlow, Wicklow, East Mayo, West Mayo, Sligo, Leitrim, Fermanagh, West Donegal, Tyrone, Antrim.
Classification. Family Hymenophyllaceae (C.T.W.); Trichomanaceae (Swale and Hassler); Hymenophyllaceae (Stace). Order Hymenophyllales (Swale and Hassler).
Comments. Petioles winged, at least distally.
Illustrations. • T. speciosum: as T. radicans, Eng. Bot. 1839 (1886). • T. speciosum: Sowerby and Johnson (1859). • Hymenophyllum and Trichomanes (inter alia).
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’.