Sagina procumbens L., Procumbent Pearlwort
Account Summary
Native, common and very widespread. Eurosiberian boreo-temperate, but very widely naturalised worldwide.
1881; Stewart, S.A.; Co Fermanagh.
Throughout the year.
Growth form and preferred habitats
S. procumbens is a very common and widespread, locally abundant, wintergreen, rosette, mat-forming, or more rarely tufted, moss-like perennial, or sometimes a ruderal, annual. The plant is often, but not always, tightly appressed to the substrate on which it grows, especially when growing in soil compacted by regular trampling. It colonises a wide range of semi-natural, open habitats, including damp, shaded cliff ledges, rocky areas or bare, sometimes marshy ground on lakeshores and river banks, and in damp, flushed areas on moors. It is also common in moist, moderately fertile, shaded artificial habitats, for instance in short, heavily-grazed pastures, lawns, by paths, ditches, crevices in pavements and at the base of walls. It is indifferent to lime and really avoids only the most acid, waterlogged, or submerged aquatic situations (Grime et al. 1988).
An all too familiar garden and plant-pot weed, at a glance the tuft of linear leaves of the sterile central rosette, and the slender spreading branches can make it look quite moss-like, especially when clones of it infest short mown grass in lawns. Numerous creeping stems arise from the sides of the flower-less, tufted central leaf rosette, and these root at intervals and can spread and interweave to form dense mats in suitable growing conditions.
As one might expect, the longevity of the individual plant is very much determined by the pattern and severity of disturbance in the particular ground it occupies, and in many artificial, anthropogenic situations, the species is almost entirely ruderal and annual. In more stable situations, it remains a persistent polycarpic perennial, and for instance has been observed surviving in a lawn for around eight years (Grime et al. 1988).
Flowering reproduction
S. procumbens has a long flowering period stretching from April to September. Plants produce short, erect, flower stalks bearing tiny, solitary, regularly or automatically self-pollinating flowers, which are often without petals or else have four (or occasionally five), minute white or greenish ones (Clapham et al. 1962). The flowers often remain closed, only opening when it is both sunny and warm. It is, therefore, probably mainly autogamous, and seed-set is good (Jonsell et al. 2001). A curious feature of S. procumbens is the way the pedicel of the developing fruit capsule flexes and allows it to droop and dangle, hook-like for a time, yet when ripe it straightens up and stands erect to release the seed!
Capsule contents vary considerably, the number of seeds ranging from 20-135 with a mean of 74. The seed is extremely lightweight, almost dust-like, and despite being released from a very low point of origin, they are very readily lifted and dispersed by the slightest breeze that crosses the open mouth of the fruit capsule (Salisbury 1942, 1964). The seed is also adhesive in mud and is very probably transported by man and other animals in this way. In common with many other members of the family, under suitable conditions this species persists for at least five years in the soil seed bank (Thompson et al. 1997).
Variation
In Scandinavia there is considerable variation in ciliation (short hairiness) of the leaves, number of sepals and petals, presence and length of the petals, and length of the mucro point on the leaf tip (Jonsell et al. 2001). In Britain & Ireland, there is considerable variation in the length of the leaf blade (0.5-1.2 cm), degree of leaf ciliation (including its absence), flower diameter (2-4 mm), sepal number (4, occasionally 5) and capsule size (2-3 mm) (Sell & Murrell 2018).
Hybrids
While selfing is the norm in S. procumbens, the fact that occasional or rare hybrids with other Sagina species are known, indicates that some out-breeding can and does occur (Stace 1975; Stace et al. 2015). No hybrid Sagina has ever been found in Ireland.
Vegetative reproduction
In areas of mild climate, established plants of S. procumbens can continue to grow almost all year round, and when cut or grazed, small stem fragments may root and regenerate the plant in open sites with damp, disturbed soil. Prostrate stems are also capable of rooting, and will form new plantlets if detached (Grime et al. 1988).
Competitive ability and survival strategy
On account of its appressed habit and low growth form, Grime et al. (1988) concluded that S. procumbens is a stress tolerant herb, unable to compete with the majority of taller and broader-leaved pasture species. However, it is flexible in both its growth and reproductive strategies, and is sufficiently variable in terms of both genetic and environmental responses, to be capable of colonising artificial and freshly available semi-natural habitats (Jonsell et al. 2001). It is able to survive and compete in vegetation that is regularly and frequently mown, trampled or otherwise considerably disturbed. It also avoids most competitors by growing in sites that provide severely limited growing conditions, such as cracks in pavement.
Fermanagh occurrence
S. procumbens has been recorded in 370 Fermanagh tetrads, 70.1% of those in the VC. Procumbent Pearlwort is abundant in damp, shady situations at all altitudes in Fermanagh, on a wide variety of soils.
British and Irish occurrence
It is common throughout the whole of Britain and Ireland, and is especially frequent in man-made, artificial habitats.
European and world occurrence
Eurosiberian boreo-temperate, native in most of Europe (including Iceland, the far north of Scandinavia and the Macaronesian islands), although rarer in the Mediterranean basin and eastern areas of the continent (Jalas & Suominen 1983, Map 917). Also present in N Africa and the mountains of W Asia. Introduced by man in many parts of the world, including N America, Australia, New Zealand (arrived c 1873), the South African Cape Region (arrived c 1845), and parts of S America (Kloot 1983; Hultén & Fries 1986, Map 762; Webb et al. 1988).
Names and folklore
The generic name 'Sagina' is Latin, meaning 'food crop' or 'fodder'. Spergula arvensis (Corn Spurrey), which was cultivated and much valued in Flanders as a fodder crop for dairy cows, or as human famine food in the 15th century, was previously called Sagina spergula (Gilbert-Carter 1964; Thirsk 1997, p. 17). The Latin specific epithet 'procumbens' means 'extend', 'spread', 'creeping forward' or 'lying along the ground', ie prostrate (Gilbert-Carter 1964; Gledhill 1985), all of which describes the typical habit of the species.
The English common name 'Pearlwort' is given to all Sagina species and was first used by John Ray in 1660. It refers to the small fruit capsule, or to the unopened flower. 'Procumbent Pearlwort' is a mere book name translation of the botanical name. Alternative names listed for this very common plant are 'Beads' (Wiltshire), 'Bird's Eye' (Sussex), 'Little Chickweed' (Somerset) and 'Poverty' (Norfolk) (Grigson 1955, 1987).
In folklore, the Pearlwort plant has special magical powers associated with a tradition that believed Christ stood on it when he first came to earth or when he arose from the dead, making it a good-luck plant (Grigson 1955, 1987). In Scotland, it was one of the plants fixed over doors for good luck, or to keep away the fairies who might spirit away the inhabitants (Grigson 1955, 1987; Vickery 1995). Grigson lists several other myths associated with cows, milk and kissing!
Threats
None.