British ferns (Filicopsida)


L. Watson and M. J. Dallwitz

Woodsia ilvensis (L.) R.Br.

Sporophyte. The rhizomes short, more or less erect; bearing scales (sparsely scaly above).

Leaves aggregated terminally; to 5–15 cm long; dying in the autumn; complexly divided; once pinnate, with conspicuously divided pinnae (the pinnae deeply lobed). Pinnae about 7–15 on each side of the leaf. The petioles shorter than the blades to about as long as the blades (from about half as long, jointed near the middle, pale reddish brown, with brown lanceolate scales below, subulate scales above, and flexuous hairs throughout); jointed and ultimately abscising in the mid-region; vascularised via a single strand. The longest pinnae about a third of the distance from the base of the blade, or around the middle of the blade (the lowest pinna scarcely shorter to considerably so); 0.7–1.7 cm long. The largest pinnae oblong or ovate-oblong, 1.5–2 times as long as broad, and the rachis and the undersides of the pinnae are densely scaly with 2–3 mm long, subulate, pale brown scales and flexuous hairs. The venation of the lamina open.

The sporangia superficial; aggregated in sori. The sori sub-orbicular (borne on the vein endings, near the margins of the lobes); remaining discrete at maturity; with a true indusium. The indusia consisting mainly of hairs; surrounding the base of the sorus, divided nearly to the base into numerous irregular lobes which terminate in long, jointed hair-points, the latter arching over the sporangium. Paraphyses absent. The mature spores monolete; without a perispore.

Distribution and habitat. Mostly on neutral substrates. Crevices, mostly in neutral rocks, from 360 m to 720 m. Very local in Caerns, Cumberland, Dumfries and Angus, formerly more widespread.

Vice-county records. Britain: Merionethshire, Caernarvonshire, North-west Yorkshire, Durham, Westmorland, Cumberland, Dumfriesshire, Angus, East Inverness-shire.

Classification. Family Polypodiaceae (C.T.W.); Woodsiaceae (Swale and Hassler); Woodsiaceae (Stace). Order Athyriales (Swale and Hassler).

Illustrations. • W. ilvensis: Eng. Bot. 1862 (1886). • W. ilvensis: Sowerby and Johnson (1859). • Gymnocarpium spp. and Woodsia spp. (inter alia).

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Cite this publication as: ‘Watson, L., and Dallwitz, M.J. 2004 onwards. British ferns (Filicopsida). Version: 4th January 2012.’.