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Hypericum humifusum L., Trailing St John's-wort

Account Summary

Native, rare or very occasional. European temperate, introduced in S Africa and New Zealand.

1884; Barrington, R.M.; Gubbaroe Point, Lower Lough Erne.

April to November.

Growth form and preferred habitats

This short-lived perennial produces prostrate, non-rooting stems that are quite distinctive. However, trailing specimens of H. pulchrum (Slender St John's-wort) should not be mistaken for this species. The best distinguishing feature between these two species is the unequal sepals of H. humifusum, two of which are shorter and narrower than the other three.

The most frequent substrate on which Trailing St John's-wort grows is bare sandy or gravelly ground. This is quite a good starting point for making a correct identification since H. humifusum is generally recognised as a pioneer of open or disturbed, light, dry or well-drained, slightly to somewhat acidic soils.

Thus it occupies a wide range of open habitats in B & I in situations where competition is virtually absent. Suitable ground generally occurs in short turf with open, bare areas on moorland, grasslands, dunes, tracks, dry wayside banks, waste ground, sand- and gravel-pits, plus on the margins of woods or in clearings. Some English local Floras indicate it can also sometimes be found growing on walls and in lawns.

Fermanagh occurrence

H. humifusum is rare in Fermanagh and occurs sparingly, either as single individuals, or just a few plants at most of its 14 Fermanagh sites. It is thinly and widely scattered across 13 tetrads in the VC and only nine tetrads contain post-1975 records.

The Fermanagh soils it occupies provide dry, bare, sandy or well-drained peaty conditions and they occur on lakeshores, riverbanks, hedgerows, waste ground and in an old sand-pit near Pubble Bridge. These fit the typical habitat range of this species in B & I quite well, except with respect to moors, woods, lawns and walls. In the case of the walls, we might substitute the cliffs at Carrickbeg, where it was recorded by Meikle and co-workers in 1947. However, on reflection, these cliffs are wooded at their base!

Apart from the first record above, the other Fermanagh station details are:

"Several localities about Boho", 1946, MCM & D; Carrickbeg Cliffs, E of Horse Rock, NW of Boho, 1947, MCM & D; Drumderg Lough, SW of Teemore, 1950, MCM & D; Bank near Church with tower, 1.5 km N of Boho, 1950, MCM & D; Pubble Bridge, Tempo River, 1 October 1988, RHN; Cradien/Ballydoolagh Tds, 3 km NE of Enniskilllen, 16 June 1989, RHN; Scarford Bridge, Colebrooke River, 2 November 1989, RHN; Near children’s playground, Castle Archdale, 2 November 1990, RHN; Drumcreen, banks of Ballinamallard River, 16 April 1995, RHN & HJN; Coolbuck Td, near Lough Eyes, 2.5 km NE of Lisbellaw, 19 October 1997, RHN; Sand pit near Pubble Bridge, Tempo River, 20 August 1999, RSF & RHN; Dry bare shale bank above Sillees River near farm, E of Melly’s Rock, 14 July 2001, RHN; and Largy Hill, 1 km S of Lack, 3 October 2002, I. McNeill.

Ecology

The typical lifespan of perennial H. humifusum in the temporary growing conditions associated with its pioneer status falls between two and four years. Its survival potential is enhanced by an adaptation enabling it to flower and fruit in its first year of growth and additionally the unopened flower buds can self-pollinate if weather conditions are unfavourable for normal open pollination by insect visitors when the flowers are ready to function (ie it displays facultative cleistogamy). However, the species is very variable and seed germinating in early autumn can produce dwarf semi-erect individuals, which may behave either as very ephemeral annuals, or as biennials if they manage to overwinter (Robson 1990).

British and Irish occurrence

H. humifusum is widespread but always local and more often scarce than abundant throughout most of B & I, but is most frequent in the S & W and is absent from the extreme N of Scotland and from the N & W isles. There appear to be considerable losses in parts of B & I, which began around 1950 and can probably therefore be attributed to changes in land-use including the intensification of farming. In parts of W Ireland, some apparent losses are more likely due to insufficient recording (N.K.B. Robson, in: Preston et al. 2002).

European occurrence

The wider distribution of H. humifusum is mainly Central European, but it extends into W Europe and NW Africa in Morocco, Madeira, the Canaries and the Azores (Robson 1990).

Threats

The closing of the sandpit at Pubble with subsequent loss of bare ground, plus the general tidying-up of the countryside, which could easily eliminate the few remaining stations.