British ferns (Filicopsida)

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L. Watson and M. J. Dallwitz

Cystopteris alpina (Lam.) Desv.

“Alpine Bladder Fern”.

Cystopteris fragilis ssp. alpina (Lamarck) Hartman; Cystopteris regia (L.) Desv.

Sporophyte. The rhizomes short, rather stout; more or less decumbent; bearing scales (these thin, tan to light brown, lanceolate). Plants with no clear distinction into fertile and sterile leaves.

Leaves aggregated terminally; to 5–35(–45) cm long; dying in the autumn; circinnate; compound; complexly divided; tripinnate with conspicuously divided ultimate pinnules (i.e., almost 4-pinnate, the utimate pinnules narrow and more or less parallel-sided at least below, more strongly divided than those of C. fragilis, and the ultimate segments more or less truncate or emarginate). Pinnae 4–10 on each side of the leaf (?). The petioles shorter than the blades to about as long as the blades (with a few scales at the base and usually a few hair-like scales above); with 2 vascular bundles. Leaf blades in outline ovate, or lanceolate. The longest pinnae about a third of the distance from the base of the blade to around the middle of the blade; 1–4 cm long. The adjacent pinnae approximated but not strongly overlapping to distant from one another and not at all overlapping (the separation becoming less marked acropetaly). The venation of the lamina open.

The sporangia superficial; aggregated in sori. The sori sub-orbicular (small, each on a receptacle with a vascular strand from the vein, borne two or three on the ultimate segment); remaining discrete at maturity; with a true indusium. The indusia not reniform but flap-like from the base of the sorus, vaulted at first, later reflexed; whitish, ovate, exceeding the sorus. The mature spores echinate; without a perispore.

Distribution and habitat. On base-rich substrates. Once native to the British Isles (and possibly still resident but overlooked). A mainland European alpine species, formerly occurring in Upper Teesdale but long extinct there.

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

Illustrations. • C. alpina: Eng. Bot. 1866 (1886). • C. alpina?: Sowerby and Johnson (1859). • Cystopteris species (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’.

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