Spergularia marina, family Caryophyllaceae (the family of Pinks and Carnations). Flowers 6-8 mm in diameter, petals pink with a white base, shorter than the sepals. Stamens 4-8 or more. Stem is somewhat glandular above, sometimes making it somewhat ‘sticky’. Photo: Chris Jeffree.
Lesser Sea-Spurry is a native plant originally found at the coast as a component of salt marshes, with rather fleshy leaves like those in many salt-tolerating species (‘halophytes’). I’ve seen it a few times in Edinburgh, and the BSBI data base shows 125 records for Midlothian since the 1950s. Some of the records are indeed coastal, including Leith docks, Musselburgh lagoons, paths by the sea and a marine esplanade. But the great majority of records are not maritime at all – they include car parks, traffic islands, roadsides and pavement edges. Yes, these days the species has come inland, thriving on the verges of salt-treated roads. It is however a bit fussy – you don’t find it on every salt-treated road and it isn’t usually dominant.
Spergularia marina, native, usually an annual, with prostrate and flattened shoots, plant not exceeding 20 cm in height. Photo: Chris Jeffree.
Since the 1960s the practice of spreading rock salt on roads in winter has become commonplace, even on minor roads. I have read that two million tonnes of salt are spread onto the UK roads each year. That’s 30 kg for every man, woman and child. Unsurprisingly several coastal species have moved inland, including Puccinellia distans (Reflexed salt‐marsh grass), Cochlearia danica (Danish scurvy‐grass) and Spegularia marina.
These three are well known examples of halophytes, broadly defined as ‘species that can tolerate high concentrations of sodium chloride (NaCl) throughout their life cycle’. There aren’t many halophytes in the British Flora. Mark Hill’s list of plant attributes (called PLANTATT) suggests they make up less than 2% of the flora.
Our most recent sighting of the Lesser Sea-Spurry struck us as remarkable. We were visiting Westhill, a suburban town just west of Aberdeen, some 15 km from the sea. It’s a new and rather tidy small town. It was built on farmland, starting in 1968; from then it has expanded gradually, keeping pace with the North East’s oil and gas economy. We headed for the retail park, and, on stepping from the car we saw a mass of Spergularia marina, more than I have ever seen in one place, thriving in pavement cracks and on the muddy ground bordering the site. Supermarkets feel the need to look after their customers and presumably their car parks are given a good dusting of salt at the first hint of a frost.
This is where we found the plant on the edge of a car park at Westhill near Aberdeen. The green material is nearly all ‘it’. Photo: Chris Jeffree.
How do plants tolerate salt, and why don’t all plants tolerate salt given that life began in the sea? These questions have occupied researchers for many decades, and if you really want to see the main attempts to answer such questions then you could dip into the article by Flowers and Colmer (2008). The simplest view is that plants can’t tolerate salt in the soil (or on their leaves, from salt-spray) because salt draws water from the plant cells by osmosis and thus causes ‘physiological drought’. But the halophytes overcome this, either by excreting salt via special glands or by storing it away in large vacuoles, making the leaves very fleshy.
We may call these plants ‘crackophytes’ – they frequently grow in cracks. Here we see Spergularia marina forming an association with several others (Plantago major the broadleaf plantain and Gnaphalium uliginosum, the marsh cudweed are also prominent here). Location: Westhill. Photo: Chris Jeffree.
All halophytes can be cultivated in normal soil but some halophytes, including S. marina have been shown to grow faster when salt is added to the soil (Cheeseman et al. 1985). It seems this is possible because sodium ions (Na+) are very similar to potassium ions (K+), and potassium is crucial in the ion transport system, performing roles in, for example, the opening and closing of stomata. So where potassium is in short supply, sodium is needed to take its place.
The other component of salt, chloride ions, was formerly regarded as a non-essential element or at best, as a micronutrient; however, to my great surprise some recent researchers think it should be regarded as a macronutrient (Colmenero-Flores et al. 2019). They emphasise its importance in photosynthesis. But I don’t think this view is widely held: and be assured I won’t be putting dilute bleach on my garden in the forseeable future.
Comparison of recent and older distributions from the BSBI database. On the left, the pattern in 1986; on the right are all records from 1987 onwards. The coastal occupancy has been consolidated but the big change is the colonisation of inland sites.
The BSBI distribution map shows that Spergularia marina was more or less confined to the coast until about 1986, but after that it began to move inland. A similar pattern is seen well beyond our own shores: a recent paper from Hungary (Fekete 2022) shows the distribution of five halophytes (including Spergularia marina) along the road network, and discusses the role of air turbulence in dispersal.
Images of the seeds. In this view, only one seed is the ‘winged’ type. © Copyright Malcolm Storey 2011-2118, prepared in accordance with the stated copyright policy of Discover Life where the image is displayed. See https://www.discoverlife.org/mp/20q?search=Spergularia+marina
As any cyclist knows, fast vehicles produce a turbulent wake, exerting an aerodynamic ‘pull’ on anything behind. This mechanism may work especially well in the case of S marina, as this species produces two kinds of seeds, winged and non-winged. The ‘wing’ is hardly a wing, more like a frilly margin (an earlier Flora calls it ‘a broad scarious border’) but nevertheless it may be enough to enhance dispersal by air. Inevitably, some of these seeds will stick to the vehicle tyres and be dispersed up and down the country. Using the distribution map, I zoomed in to look at the relation between records and roads. They do relate; but the overwhelming relationship is with the density of human populations. I suppose the seeds wash off the tyres of parked cars when it is raining.
A close look at the Scottish records (all records). The species is concentrated in urban areas with some records along major trunk roads (like the M90 but not like the A74). BSBI data.
The discovery of Spergularia marina as a British native species was in 1632 by Yorkshireman Thomas Johnson, know as the ‘Father of British Field Botany’. He is best known for his work on updating Gerard’s Herbal: he added over eight hundred new species to the list, and seven hundred figures, besides making numerous corrections. The species was named and properly described by Linnaeus in 1753. It was named Alsine marina: you can find images of ‘type specimens’ from the Natural History Museum here . In Spergularia marina (L.) Griseb., the format refers to the first description by L (i.e. Linnaeus) and the revision by Griseb. (the name ’Griseb’. is the standard abbreviation for the botanist August Heinrich Rudolf Grisebach, 1814-1879, of the Göttingen University).
References
Cheeseman JM (1985) Salinity tolerance in Spergularia marina. Canadian Journal of Botany. Find it here.
Colmenero-Flores JM et al (2019) Chloride as a Beneficial Macronutrient in Higher Plants: New Roles and Regulation. International Journal of Molecular Science 20(19), 4686.
Fekete R et al (2022) Road traffic and landscape characteristics predict the occurrence of native halophytes on roadside verges. Scientific Reports 12, 1298
Flowers TJ & Colmer TD (2008) Salinity tolerance in halophytes. New Phytologist 179, 945-963.
©John Grace
Botany in Scotland 