Polystichum lonchitis (L.) Roth, Holly-fern
Account Summary
Native, very rare. Circumpolar boreo-temperate.
July 1979; Northridge, Mrs H.J. & Northridge, R.H.; cliff 1 km SE of Lough Achork, in the Lough Navar Forest Park.
Throughout the year.
Growth form and preferred habitats
Holly-fern produces its glossy, evergreen, rather leathery fronds in shuttlecock-like rosettes from a short, stout rhizome, often embedded in tight crevices on exposed rock faces. The English common name 'Holly-fern' is not really all that appropriate, since it is not 'holly-like' at all, except in that the simply pinnate fronds are definitely evergreen (each persisting two or three years). The fronds are shiny, and the individual pinnae bear teeth that look rather spiny, but are really quite flexible. Both the growth of fronds and the establishment of new plants are slow, but compensating for this fact, individual plants and fronds are clearly long-lived.
P. lonchitis is a definite calcicole, being confined to calcareous or base-rich rocks, which includes the dolomitised sandstone it frequents in Fermanagh. The species typically grows in cool, moist, well-drained positions at the base of cliff faces, or in crevices on or near ledges. In numerous sites, it frequents stabilised boulder scree and, in England, occasional plants of P. lonchitis are found in moist, deep grykes in limestone pavement and around the entrances of sinkholes.
Fermanagh occurrence
One plant of this species is known to have survived for 30 years at its site in a crevice on a N-facing dolomitized sandstone cliff in Lough Navar Forest (Northridge et al. 1988). In 2000, the original plant was joined by a small plant 20 cm higher on the cliff, which we regard as most probably an offspring of the established plant. By 2010, there were five plants at the site, the original plus two small daughter rosettes slightly higher up on the cliff face, plus two nearly mature rosettes on the ground at the base of the rock face, which previously had been overlooked.
In June 1999 R.D. Porley, an English bryologist, surveying mosses and liverworts on the Lough Navar scarps for the Environment and Heritage Service, found another small plant which he identified as P. lonchitis on Bolusty Beg, almost exactly 2 km due north of the earlier known station. The present author and his Botanical Society joint-Vice County Recorder, Robert Northridge, only discovered this claim when the bryological results were published in September 2002 (the Irish Naturalists’ Journal was a year late in its appearance). In 2003 Robert Northridge visited the site and saw an immature Polystichum plant near a red marker stick. The plant was too immature to determine to species level. On 1 February 2004, RHN revisited the site and the plant had matured enough for it to be determined as P. aculeatum (Hard Shield-fern). It is difficult to distinguish juvenile specimens of these closely related ferns and the mistaken identification is a perfectly understandable one.
P. lonchitis is a circumpolar arctic-alpine species, and at its Fermanagh site it grows beside a plant of Asplenium viride (= A. trichomanes-ramosum) (Green Spleenwort), another northern or arctic-alpine species similarly confined to calcareous or other base-rich rock habitats. Normally both these species occur in upland areas in Britain and Ireland, which are typically cool in summer (summer maximum around 27C), and where base-rich pockets of soil are kept permanently moist by water seepage (Page 1997).
Sori are produced on the top portion of the frond only, and spores are released from mid-summer until the following spring. Clearly conditions at our Fermanagh site are suitable for reproduction, since new young plants have become established near the original specimen in recent years. Apart from the well-colonised stable block scree stations in Glenade, Co Leitrim (H29) (the undoubted Irish headquarters of the plant, where the species grows large, luxuriant clumps), Holly-fern occurs in most of its Irish sites as small, widely scattered, individual cliff crevice plants. It is quite possible that somewhere in the Lough Navar area another plant might occur on nearby cliffs or screes of suitable rock chemistry.
Irish occurrence
The plants at the solitary Fermanagh site are the only representatives of this species known from Northern Ireland, although elsewhere in the Republic of Ireland there are a few scattered localities down the W coast in Co Donegal (H34 & H35), Co Leitrim (H29) (definitely its Irish headquarters), Co Sligo (H28), Mayo (H27), Co Galway (H16) and Kerry (H1 & H2) (Jermy et al. 1978; Census Catalogue of the Flora of Ireland 2).
In limestone pavement in N England, occasional plants of P. lonchitis are found in moist, deep grykes and around sinkhole mouths, making it all the more odd that the species is absent from the identical habitats which are so vastly more abundant in the Burren district of Co Clare. Having said that, A. viride (Green Spleenwort) is another inexplicable Burren fern absentee.
British occurrence
In Britain, P. lonchitis is similarly rare and local from N Wales, N England and S Scotland, but it becomes more widespread in the mountains of C & NW Scotland (Jermy et al. 1978; Page 1997). The records in the 1978 Fern Atlas suggest that there may be a contraction in the number of sites for Holly-fern in parts of Ireland, England and Wales, but this does not appear to apply in the main area of the species in N & W Scotland (Jermy et al. 1978). In limestone pavement in N England, occasional plants of P. lonchitis are found in moist, deep grykes and around sinkhole mouths.
European and world occurrence
In Europe, P. lonchitis is widespread in cooler areas, ie montane and high latitude regions. The distribution extends northwards along W Scandinavia reaching well inside the Arctic Circle. The species is also present in Iceland and the Faroes. In continental Europe, it is mainly associated with the Alps, Pyrenees and other outlying mountain areas, reaching its southern extremities in SE Spain, Italy, Corsica, the Peloponnese and W Crete (Jalas & Suominen 1972, Map 119). The overall European distribution pattern is remarkably similar to that of Asplenium viride (= A. trichomanes-ramosum), Green Spleenwort (Jalas & Suominen 1972, Map 83). As in the case in Dryopteris carthusiana (Narrow Buckler-fern), P. lonchitis in Scandinavia occupies a much wider range of habitats than it does in the British Isles, including forest (deciduous forest as well as mixed and spruce forest), together with crevices in lava-fields, and even occasionally on man-made structures e.g. stone walls ('stone-fences') (Jonsell et al. 2000).
Beyond Europe, Holly-fern ranges around cooler parts of the northern hemisphere in a circumpolar manner from the Caucasus, the N Urals, mountains of C Asia, the W Himalaya, Japan, W and NE North America and Greenland (Hultén 1958, Map 219; Jonsell et al. 2000).
Names
The genus name 'Polystichum' is derived from two Greek words 'polus', 'many', and 'sticos' or 'stichos', meaning 'row' or 'file'. Taken together 'many rows' is a reference to the regularly arranged rows of sori on the fertile frond (Gilbert-Carter 1964). The specific epithet 'lonchitis' is a Latinised form of the Greek 'loncho' meaning 'spear-shaped' or 'lance-shaped', obviously referring to the outline of the frond. It was also a name given to an unknown fern by Dioscorides (Gilbert-Carter 1964; Gledhill 1985).
The English common name, 'Holly-fern', is a rather curious one, the only similarities between the two plants being the evergreen, thick textured leaves. The numerous teeth on the fern pinnae only look prickly or spiny, but are in fact quite soft, unlike the real Holly's leaf prickles. In common with the 'Oak Fern' and 'Beech Fern', there is no ecological linkage between the fern appellation and the tree for which it is named, and one is left to wonder at the philosophy behind the obscure names humans give to the things about them!
Threats
The Fermanagh Holly-fern station is vulnerable having survived one extensive fire on its cliff in recent years; another such event could easily destroy it.