Lysimachia maritima – June 30th 2025 – Sea Milkwort
Last week we went north to Orkney for a short botanical exploration of its main town, Kirkwall. I was especially interested to see the coastal vegetation, although Kirkwall’s coast turned out to be mostly mown grass and concrete. Undeterred, I strolled on a stretch of wet and windy shoreline with my waterproof notebook, to see what I could find. A small plant with flowers like rubies caught my eye. I know it as Glaux maritima but now we should use its new name Lysimachia maritima, Sea Milkwort, in the Primula Family (Primulaceae).
Lysimachia maritima, Sea Milkwort at the strandline, Kirkwall, Orkney 26th June 2025. Image: John Grace.
This is a plant that tolerates salt (a ‘halophyte’). You don’t have to go to Orkney to see it as the plant is found all around our coast, but it is not common. It sometimes grows inland, as a roadside plant along salted roads and it has been recorded on the somewhat-salty shores of the River Thames in London. It is an extreme halophyte: in Kirkwall it was looking healthy at the strand-line where debris is deposited at the high water-mark, and crispy dried-out seaweed traps the wind-blown sand particles.
Lysimachia maritima, at a saltmarsh in Mersehead, SW Scotland, growing with Salicornia, grasses and Plantago maritima. Image: Chris Jeffree.
It is a biennial native plant, with shoots that creep along the soil and form roots. It was first described by Flemish physician-botanist Matthias de l’Obel in 1571, who often travelled to England and became the Royal Botanist to King James the First. He maintained a botanical garden in Hackney, and the plant Lobelia is named after him.
There is renewed interest in halophytes, as much of the world’s land surface is now too salty for crop plants to grow, and so many researchers are trying to develop salt tolerance in cereals and other possible food plants. The native plant Beta maritima and its domesticated relatives beetroot and sugar beet are halophytes, and so is the related South American ‘pseudocereal’ Chenopodium quinoa.
Close-up images to show the arrangement of flowers. The ‘petals’ are coloured sepals (there are no true petals), and they arise in the leaf axils. Sepals and stamens are five per flower. The leaves are somewhat fleshy and the salt-secreting glands on the leaves appear as white dots. Images: Chris Jeffree.
Plants need very little sodium Na+ but lots of potassium K+. As anyone studying school-level chemistry knows, these elements are very similar. Plants take up K+ by actively pumping the ions into their cells, but alas the pump also brings in much unwanted Na+. In a saline soil this is enough to poison most plants but halophytes can deal with the problem. Some of them store the salt in vacuoles, out of harm’s way. Their leaves therefore look ‘succulent’. Others secrete salt: in Lysimachia maritima there are salt-secreting glands on the leaf surface (Jelte and Riphagen 1977). In Chenopodium quinoa there are ‘epidermal bladder-cells’ where salt is dumped.
Distribution of Lysimachia maritima in Britain and Ireland. From BSBI/Maps.
Researchers are these days using Arabidopsis thaliana as their model plant to understand salt stress. This little plant is the favourite of molecular biologists because it is easy to grow, flowers in six weeks, and much is already known about it. A few populations of this plant can tolerate salt, and these ecotypes are being investigated for their ‘Salt Overly Sensitive (SOS) pathway’. But, I wonder, shouldn’t researchers be looking at the real halophytes instead of concentrating on just one species? After all, plant life began in the sea, and salt tolerance was largely ‘lost’ during the conquest of the land. We need to find it again by looking at the diversity of life.
References consulted
Choi JH et al (2024) The Arabidopsis thaliana ecotype Ct-1 achieves higher salt tolerance relative to Col-0 via higher tissue retention of K+ and NO3–, Journal of Plant Physiology 302, https://doi.org/10.1016/j.jplph.2024.154321
Edgington JA (2004). Sagina maritima Don (Caryophyllaceae) and other halophytes in London. Watsonia 25, 121-126.
Fiorillo A, Manai M, Visconti S, Camoni L. (2023). The Salt Tolerance-Related Protein (STRP) Is a Positive Regulator of the Response to Salt Stress in Arabidopsis thaliana. Plants (Basel). 12(8):1704. doi: 10.3390/plants12081704.
Jelte R and Riphagen I (1977). Physiology and ecologic relevance of salt secretion by the salt gland of Glaux maritima L. Oecologia 29, 349-357.
Jelte R, Riphagen I and Sminia T (1977). A light and electron-microscopical study on the structure and function of the salt gland of Glaux maritima. New Phytologist 79, 665-671.
Edgington JA (2004). Sagina maritima Don (Caryophyllaceae) and other halophytes in London. Watsonia 25, 121-126.
Pardo JM and Quintero FJ (2002). Plants and sodium ions: keeping company with the enemy. Genome Biol. 2002;3(6):REVIEWS1017. doi: 10.1186/gb-2002-3-6-reviews1017.
Notes
The image at the top of the page is by Chris Jeffree, showing Lysimachia maritima growing in the sand at North Berwick.
©John Grace
