Onoclea sensibilis L., Sensitive Fern

Account Summary

Growth form and preferred habitats

In Britain, this deciduous, rhizomatous, perennial garden species of North American and Eastern Asian origin is a widely scattered, but quite frequent established garden escape or discard. It tends to colonise wet lake margins and areas where ground water seeps. Other typical habitats include damp woodland marshy meadows and riversides. The plant, which is frequently grown in gardens, has a horizontally spreading rhizome which quickly spreads allowing this attractive fern to form large clonal patches. The fronds are heterophyllous, the plant producing yellow-green pinnatifid fronds up to 90 cm tall and separate, shorter, purplish-brown, fertile fronds that bear bead-like sori tightly clustered like grapes.

Since it may quite rapidly outgrow available garden space, Sensitive Fern gets passed around between gardening acquaintances and also becomes discarded in refuse tips or in areas of waste ground where fly tipping takes place (Clement & Foster 1994). The species may also spread naturally by means of its spores and colonies in Britain have been reported considerable distances from habitation. There is some evidence that this species is currently spreading in Britain at least (T.D. Dines, in: Preston et al. 2002).

Fermanagh occurrence

A recent, solitary record exists in the Fermanagh Flora Database of a large, well-established patch that was found growing beside a stream in the outer Pleasure Grounds of Florencecourt House, in an area that otherwise appeared unplanted.

British occurrence

O. sensibilis is mainly distributed in S & W parts of Britain and according to Jermy & Camus (1991) has also been reported in Ireland. Oddly, in view of this, there is no mention of it in the Catalogue of Alien Plants in Ireland (Reynolds 2002), and while it is mapped in the CD-rom distributed with the New Atlas, the latter plots no hectads for Ireland.

Names

'Onoclea' is from the Greek 'onos', meaning 'vessel', and 'kleio', 'to close', referring to the closely rolled pinnules of the fertile fronds that enclose the sori. The Latin specific epithet 'sensibilis' means 'sensitive'. The English common name 'Sensitive Fern' originates in N America where the fronds are observed to be very sensitive to frost, the aerial parts quickly collapsing and dying off when first touched by it. An alternative common name, 'Bead Fern' refers to the bead-like sori (http://rook.org/earl/bwca/nature/ferns/onoclea.html)(accessed Nov 2014).

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