Galium palustre L., Marsh-bedstraw

Account Summary

Growth form and preferred habitats

A very common, indeed almost ubiquitous slender perennial of both seasonal and permanently wet ground everywhere in B & I, G. palustre has a slender creeping rhizome or rootstock from which decumbent, scrambling and weak ascending stems arise, sometimes up to 100 cm tall, but often closer to 30-50 cm or so. The aerial stems are slender, much-branched, leafy and 4-angled, usually with very small, downwardly directed pricklets on the whitish stem angles. Lanceolate leaves, 5-20 mm long, one-veined, are borne in whorls of four to six, and the species is readily distinguished by their blunt rounded or subacute tips lacking a point or bristle (Stace 1997; Parnell & Curtis 2012).

This is a very constant member of the tall-herb wetland community in wet mud and damp, intermittently flooded ground around the margins of lakes, ponds, streams and ditches. Marsh-bedstraw grows on a wide variety of moderately fertile soil types in marshes, fens, bogs and wet hollows in meadows and woodlands, especially where these habitats are winter flooded or temporarily submerged after periods of heavy rainfall (Garrard & Streeter 1983). It grows and competes well on both acid and calcareous soils, mainly in the pH range 5.0-7.0, preferring non-calcareous substrates (W.R. Meek, in: Preston et al. 2002). It reaches a maximum altitude of 825 m in Britain at Cross Fell in Cumberland (VC 70). In many of the wetland communities it frequents, G. palustre is regularly accompanied by Juncus effusus (Soft-rush), J. acutiflorus (Sharp-flowered Rush), Mentha aquatica (Water Mint), Myosotis scorpioides (Water Forget-me-not), M. laxa (Tufted Forget-me-not) and Ranunculus flammula (Lesser Spearwort) (Sinker et al. 1985; Grime et al. 1988, 2007).

Observation suggests that G. palustre is ecologically restricted to wetland sites where the vigour of potential dominant species is to some extent suppressed by commonly occurring deleterious growth factors, such as a degree of shade, moderate disturbance (including grazing, trampling and flooding), or these plus some degree of nutrient stress. The established strategy of G. palustre is categorised as C-S-R/CR, meaning it is intermediate between a balance of all three ecological strategies, Competitor, Stress-tolerator and Ruderal, and a Competitive Ruderal. Survival appears to depend upon opportunistic expansion into small gaps in the canopy of tall growing wetland, generally waterside vegetation. Lateral expansion by vegetative growth of rootstock or rhizome and spread of decumbent stems is probably important and greatly involved in achieving this type of clambering, colonising endeavour (Grime et al. 1988, 2007).

Variation

The G. palustre aggregate forms a polyploid series in B & I (BSBI Plant Crib 1998). Two of the three subspecies or segregates of the species aggregate occur in Ireland, the smaller subsp. palustre (rarely over 50 cm tall) and the apparently rarer, larger- and later-flowered and taller growing subsp. elongatum (C. Presl) Arcang. (Great Marsh-bedstraw) (Stace 2019). The flowers of subsp. elongatum are 4.5 mm in diameter and those of subsp. palustre 3 mm diameter (Butcher 1961). An Irish Flora (1996, 2012) suggests that the characters used in Britain to distinguish these two subspecies do not correlate well in Irish plant material.

Reproduction, vegetative and sexual

Marsh-bedstraw reproduces both by seed and by vegetative lateral spread involving both local growth and fragmentation into flowing water followed by rooting of the transported cuttings. Flowering takes place in June and July, the inflorescence being a lax, straggly, cymose, leafy panicle of c 100 small white flowers, 3.0 × 4.5 mm in diameter. Each final cluster of the inflorescence has a pair of leafy bracts at the base of the long pedicel stalk (Hutchinson 1972). Pollination is carried out mainly by bees and the fruit is the usual pair of single-seeded mericarps or nutlets, 1.2-3.5 mm, globose, varying from smooth to rugose or wrinkled, hairless, on spreading pedicels. The nutlets of subsp. palustre are smaller, 1.2 mm diameter, compared with those of subsp. elongatum, 1.6 mm diameter (Butcher 1961; Sell & Murrell 2007).

Dispersal

Disturbance by grazing animals may assist dispersal, since as with other wetland species, detached plant fragments can float off and, in this instance, readily root and re-establish thus propagating the species within the water system (Grime et al. 1988, 2007). Seeds can survive ingestion by cattle, and they can also float for several weeks, helping to propagate the species if they settle in suitable growing conditions (Ridley 1930). Seed is very probably also transported to more remote, isolated habitats in mud attached to passing animals, including birds, plus man and his machinery.

Established plants with rhizomes or rootstocks overwinter as small shoots (Grime et al. 1988, 2007). Seed germination takes place mainly in spring and a proportion of seed is long-persistent in the soil seed bank (Thompson et al. 1997).

Fermanagh occurrence

G. palustre is the sixth most frequently recorded vascular plant species in the Fermanagh Flora Database, and, of the ten most frequent species in the VC, it ranks eighth in terms of tetrad frequency (ie 401 tetrads = 76%). G. palustre occurs in a wide range of habitats including bogs, fens, ditches, muddy, marshy ground and in wet meadows, especially when these are winter flooded. It is very widespread across Fermanagh, but particularly common around Upper Lough Erne. This may be, however, an artefact of local, excessively detailed recording by DOE habitat surveyors during the mid-1980s.

British and Irish occurrence

G. palustre s.l. is very common and widespread throughout the whole of B & I, occurring in every VC. Despite the widespread destruction of wetlands that has taken place across the whole land mass since the first BSBI Atlas in 1962, there is no evidence of any reduction in the distribution of the species in the New Atlas survey that was completed in 2000. This probably reflects the considerable colonising ability of the species that allows it to occupy new standing water habitats (W.R. Meek, in: Preston et al. 2002).

European and world occurrence

G. palustre belongs to the Eurosiberian boreo-temperate phytogeographical element and is widely distributed throughout most of Europe and extends from the Caucasus to W Siberia. Also present in N Africa and eastern N America and thus a member of the amphi-atlantic plants. It is introduced in Argentina and New Zealand (Hultén & Fries 1986, Map 1519).

Names

The genus name 'Galium' is a name in Dioscorides derived from the Greek 'gala', 'milk', that was first given to Galium verum, a herb widely used to curdle milk for cheese making (Johnson & Smith 1946; Gilbert-Carter 1964). The Latin specific epithet 'palustre' is from 'palus' and 'ūdis' meaning 'swamp', 'bog' and thus 'growing in a swampy place' or 'of boggy or marshy ground' (Gilbert-Carter 1964; Gledhill 1985). The English common name 'Marsh-bedstraw' is a perfect example of a recently invented 'book name' that has no attached history, folklore or poetry to recommend it.

Threats

None.

References

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