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Samolus valerandi L., Brookweed

Account Summary

Native, occasional or locally frequent. Circumpolar southern-temperate.

1900; Praeger, R.Ll.; Co Fermanagh.

April to November.

Growth form and preferred habitats

In B & I, rather limited, often, but not always transient populations of this small, thinly scattered, rosette-forming perennial most frequently occur as a salt-tolerant species of regularly or seasonally flooded or flushed, constantly wet, brackish coastal marshland, dune-slacks and cliff ledges (Flora of Co Dublin). At the same time, S. valerandi is less frequently found at inland sites and, in Ireland, it locally occupies suitable damp ground around many of the larger limestone lakes of the lowland West and Midlands. Likewise, in Britain, S. valerandi is occasionally found inland, mainly along the River Severn and its feeders and around the Wash. S. valerandi might even be considered a member of our freshwater aquatic flora, since occasionally it grows in ± waterlogged, spring-fed, fen, flush or ditch situations (Cook 1998).

S. valerandi is a pioneer colonist of bare, muddy, clay or peat, of damp to wet, but otherwise mesic or nutrient-poor, lime-rich, but typically warm, sunny growing conditions. The species has both exacting ecological requirements and extremely limited competitive ability. Despite this, it is tolerant of some degree of trampling and of light grazing pressure (Sinker et al. 1985). A certain level of disturbance obviously helps keep the habitat open, limiting the growth of potential competitors. On the negative side, however, these very specific habitat conditions must also curtail the growth of individual Brookweed plants, restricting their ability to reproduce and thus limiting the frequency and distribution of the species.

Fermanagh occurrence

In Fermanagh, S. valerandi has been recorded in 67 tetrads, 12.7% of those in the VC. However, only 56 squares have post-1975 records, strongly indicating population losses. Brookweed is an occasional or locally frequent species, found mainly on the shores of our larger lakes and especially around Lower Lough Erne. Smaller lakes where it occurs include Doagh, Carrick, Bunnahone, Ross Lough near Carr Bridge and Carran Lough, north of Boho. It was once found in quarry pools adjacent to Keenaghan Lough and it has also been recorded at Roosky, the site of important turloughs (ie vanishing limestone lakes).

Flowering reproduction

Although S. valerandi plants are small, usually only around 30 cm tall, they can take several years to flower and then most of them prove short-lived. Thus, effectively, Brookweed is a monocarpic perennial (A.J. Richards, in: Preston et al. 2002). The tiny, white or pinkish, 5 mm diameter Primula-like flowers are produced in racemes between June and August and are usually automatically self-pollinated (Clapham et al. 1962). The corolla tube is extremely short and no nectar is produced, so insect visits are rare. Average seed production has been estimated at around 3,000 per plant (Salisbury 1942, p. 203).

The fact that plants can occasionally occur on wet coastal cliffs strongly implies that wind is important in dispersal of the light seed. However, transport in mud on the feet of birds and other animals is also significant, allowing the species to transfer between isolated or unconnected water bodies (Ridley 1930, p. 545).

British and Irish occurrence

Brookweed occurs scattered around the whole coast of Ireland, and in Britain it stretches northwards to the Outer Hebrides and Orkney as a rarity. On the E coast of Britain it only reaches north as far as the Firth of Forth (Preston et al. 2002). On both islands, there has been a definite decline in the presence of the species in the last 70 years or so, mainly due to drainage.

European and world occurrence

Frequent and widespread in coastal and temperate Europe and around the Mediterranean basin, but inland it rapidly becomes scarce, scattered and increasingly disjunct, although it does stretch eastwards into S & SE Asia. Beyond Europe, S. valerandi is very widely scattered around the world in both hemispheres, including in Ethiopia, C & S Africa and E Australia, giving it a discontinuous circumpolar distribution.

The form in N & S America is subsp. parviflorus (Raf.) Hult. It is sometimes regarded as a separate species, although the differences between the two subspecies do not appear to be very fundamental and there seem to be overlapping forms on both continents (Hultén 1971, page 148; Hultén & Fries 1986, Map 1485).

Threats

Local drainage operations and eutrophication producing increased competition.