Oysterplant (Mertensia maritima) and Sea Sandwort (Honckenya peploides) growing on Orkney.

A few weeks ago a lady from Northern Ireland contacted me and told me about some of the plants she’d seen for the first time in her local area in 2018, one of which was Oysterplant. It’s a favourite of mine, but a plant I rarely see.

Oysterplant, Mertensia maritima, is a beautiful perennial that grows on sand, gravel and shingle beaches. It grows close to the ground with a spreading habit, with blue-grey leaves and, from June to August, clusters of reddish flowers that turn blue as they age, in a similar way to Forget-me-nots and several other members of its family, the Boraginaceae. (I have previously written about some of these: Green Alkanet, Viper’s Bugloss, Navelwort and Abraham-Isaac-Jacob.) There are some lovely pictures of it on the West Highland Flora and UK Wild Flowers websites.

Mertensia maritima has a large taproot that reaches down through sand or shingle to find water, as well as anchoring the plant in its exposed habitat. In winter the leaves die back to ground level. The plant spreads by seed (nutlets) and these can be transported by wind and sea and have been known to travel at least 450 km (280 miles). Germination is unaffected by up to 18 days of immersion in sea water and the seeds are capable of staying dormant for several years, until the right conditions trigger germination (note 1). Flowers appear to be mostly self-pollinated in Northern Ireland but in some places (such as on Svalbard) they are visited by insects.

Sometimes the plant occurs as a casual for just a few years before being washed away by storms but colonies can persist for hundreds of years when conditions are right. (Plants growing in pure sand are usually short-lived.)

Mertensia maritima is very much a plant of northern areas. In the British Isles it can now be found in Scotland (especially Orkney and Shetland) and Northern Ireland. In Northern Ireland it is on a list of Priority Species;  the plant also features in a 1992 article in the Irish Naturalists’ Journal. There are pre-2000 records from Northern England, North Wales and the Isle of Man, but the plant is contracting its range in the south and expanding its range further north. Further afield, the plant grows in Svalbard, Franz Joseph Land, Iceland, Greenland, North-east Asia and North America, including Canada and, in the United States, New England (note 2). Its southern limit more or less corresponds with the mean January isotherm of 4.5 °C and the mean July isotherm of 19 °C.

With its northern distribution, Mertensia maritima may well be adversely affected by climate change (note 3). The Online Atlas of the British Flora gives storms, recreational pressures, shingle removal and grazing as reasons for losses. Like the Sea Pea (Lathyrus japonicus) that I wrote about in August 2017, visitor pressure may be very significant.

Here are some examples of the threats to Oysterplant:

• Shingle removal severely damaged one of Northern Ireland’s populations of Oysterplant, at Glassdrumman Port in County Down.
• Grazing by sheep limits the distribution of Oysterplant in much of Orkney and Shetland. However, on Fair Isle fencing was used to protect the only colony and, as a result. a population of two plants in 1992 had become 2,360 plants twenty years later.
• Plants in Abergele in North Wales were apparently finished off by a combination of uncontrolled dogs and storms.

I’ve only seen Oysterplant twice and in both cases the location of the plants made my memories stronger.

I first saw the plant in 1997 on a a three week cycling trip in Iceland. While we were camping in Reykjavik we walked down to the harbour to look at the Sun Voyager. The sculpture was lovely and so was the Oysterplant growing on the shoreline nearby.

The second sighting was on another cycling trip, this time in 2006, on Orkney. We were camping in Kirkwall and decided to visit South Ronaldsay for the day. Cycling south to the Tomb of the Eagles at the far end of the island we crossed the Churchill Barriers (note 4).  Oysterplant was growing in a sandy area next to one of the Barriers.

The leaves of Mertensia maritima are edible, both raw and cooked, as are the flowers and root, but the plant is so uncommon that I don’t recommend picking it from the wild. The name “Oysterplant” comes from the taste of its leaves.

Several plants are described as “tasting like oysters”, including Salsify, which I have written about, and its close relative Scorzonera, but I’m not too convinced about the similarity.

The Plants for a Future website has a similar opinion of Oysterplant. “No-one has yet noticed a resemblance to oysters though not many of the tasters have ever eaten oysters! The flavour is fairly bland, the leaf is thick and has a very mucilaginous texture – it is probably this texture that reminds people of oysters.” I’ve eaten and enjoyed oysters a few times. It is the texture, combined with a fresh sea water saltiness, that defines the experience for me, rather than any strong taste.

But in “Flora Britannica”, Richard Mabey quotes a man in Scotland who has Oysterplant growing on his local beach. “I was once poisoned by an oyster and I can’t abide them. The taste of the leaf made me retch, so true is it to its name” (note 5).

The Edible Wild Food website says that “leaves can be added to salads, and they go quite well with eggs”. The Edible Garden Nursery website suggests that the leaves can be used “in fish dishes or salads.”

Oysterplant is often difficult to cultivate and is very susceptible to slug damage. Plants don’t like root disturbance and are most likely to succeed in well-drained sandy or gravelly soils in a sunny position. I haven’t tried growing it and I suspect it would be too hot for it here in Norfolk. However, if you like a challenge, why not give it a try? If you live in the UK, plants are available (to pre-order) from The Edible Garden Nursery. The Dave’s Garden website lists people in America and Europe who may be able to supply the plant. Oysterplant can also be grown from seed.

Other English names for Oysterplant include Seaside Bluebells, Sea Lungwort and Gray Oysterleaf.

Mertensia is named after the German botanist Franz Carl Mertens (1764 – 1831). The genus also includes American species such as Mertensia ciliata  (Fringed Bluebells) and and Mertensia virginica (Virginia Bluebells).

Notes

Note 1: The germination rate of seeds is increased improved by exposure to temperatures of 2°C or below. The British Wild Plants site is understandably gloomy about the plant’s return to Wales: “… the … seeds … must have a prolonged period in the cold sea water below 5C and then some time on cold pebbly beach in order to scrape the hard outer coat of the nutlets and allow germination to begin. The winter seas around Wales are far too warm now and it will probably never return.”

Note 2: The Flora of Svalbard describes three subspecies of Mertensia maritima. These are ssp. maritima, ssp. tenella and ssp. asiatica. Mertensia martima in the British Isles and New England is ssp. maritima, while ssp. tenella occurs in Svalbard. (I have been to Svalbard but annoyingly, I can’t remember seeing Oysterplant – I think I would have remembered if I had.)  Ssp. asiatica is found by the Pacific Ocean.

Note 3: Mertensia maritima is specfically mentioned in the MCCIP report “Impacts of climate change on coastal habitats” – L. Jones, A. Garbutt, J. Hansom and S. Angus (2013), MCCIP Science Review 2013: pp167-179. Climate change may lead to more storm surges, increases in temperatures and changes to rainfall (see page 172 of the report).

Note 4: The Churchill Barriers were built in the Second World War to protect Scapa Flow from enemy submarines and ships. They are now used as causeways to provide a road link from South Ronaldsay to Orkney’s Mainland, via Lamb Holm, Glimps Holm and Burray.

Note 5:  Richard Mabey (1996): “Flora Britannica“, Sinclair-Stevenson, London. Page 310.