Sedum rosea (L.) Scop., Roseroot

Account Summary

Growth form and preferred habitats

A grey-green (glaucous), leafy, tufted succulent perennial up to 30 cm tall with a thick, fleshy, branched stock. The stems are often flushed with purple. The small, dull yellow flowers borne in dense, flat terminal clusters are unisexual and are produced on separate plants (ie dioecious = 'two households'). S. rosea appears to prefer inaccessible crevices and rock ledges on damp to wet cliffs, often but not always of base-rich or limestone geology.

Fermanagh occurrence

Although Robert Northridge and the current author have made several searches in the appropriate cliffs and surrounds for this 'mountain plant', all attempts to rediscover the solitary reported Fermanagh station of this familiar and distinctive succulent species have to date been completely unsuccessful. However, the area involved is large and of very difficult access, so it is conceivable that it might yet survive somewhere along the cliffs where Praeger recorded it in 1904. In his wonderful account of his very energetic five days spent, Among the Fermanagh Hills, Praeger (1904) wrote almost casually of finding this species, "At one spot near the summit of the Poulaphouca western cliffs." The Cliffs of Magho and Poulaphouca are alternative names for this range of precipices, which, whenever a clear day allows, provide a fine overview of Lower Lough Erne to the north.

Irish occurrence

The next nearest known station for Roseroot is on the Carboniferous limestone cliffs of the Ben Bulbin range in Cos Leitrim and Sligo (H29 and H28), around 12 km due west. In these latter stations, the species is locally abundant and the New Atlas map indicates that a number of post-1986 records exist. It is also well represented in W Donegal (H35) both on mountains, on sea cliffs and even in damp rock crevices right down to high-tide level on west-facing Atlantic beaches.

Elsewhere in Ireland, Roseroot has previously been recorded on most of the higher mountains, nearly all of which are coastal. In NI, this includes the Mourne Mountains in SE Co Down (H38) and the NE Co Antrim cliffs, around Fair Head (H39). In several of its other Irish stations, S. rosea has become scarce or even rare during the last four or five decades, and in others it has not been seen at all for quite some years. The latter category includes, in addition to the Fermanagh site, the Wicklow hills (H20), and several of its previous N Antrim sites.

British occurrence

The New Atlas hectad map shows S. rosea is predominantly a mountain and coastal plant of NW Scotland and the Scottish Highlands & Islands, although also present on the higher mountains of England and Wales. A small number of isolated stations scattered about in England and Wales are presumably garden escapes.

Flowering reproduction

The fact that S. rosea has separate male and female plants and is thus a ± obligatory out-breeder (dioecy is rarely absolute), may become a detrimental factor seriously affecting seed production and endangering species survival whenever isolated populations decline to small numbers (Richards 1997a). We do not know the size of the minimum viable population necessary in the short term to protect against inbreeding depression, but in animals, which have a great deal more mobility than plants, the equivalent figure is often taken as 50 (Briggs & Walters 1997, p. 417). Any imbalance of the sexes would exacerbate this type of numerical problem. Clearly populations of both rare plants, and more isolated populations of scarce species, are endangered by any degree of further decline.

Species like S. rosea, which are relict survivors from past colder climatic phases in our island history, are also increasingly threatened by recent trends in global warming.

Threats

Genetic erosion in small, isolated populations, plus rapid modification of the environment associated with climate change.

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