Nov

Dianthus deltoides – 13th November 2023 – (Maiden Pink)

Some of you may have read that native plants are in decline whereas aliens are increasing. This week we focus on a native species that is in steep decline.

The Maiden Pink, Dianthus deltoides is a perennial species, in the Family Caryophyllaceae, the family that includes pinks and carnations, and also the campions, chickweeds, stitchworts and spurreys. It is a plant of short grasslands and rocky outcrops, usually found on thin, base-rich soils, frequently on banks, rarely on acid or wet soils. Braithwaite (1994) writes that in Derbyshire it occurs with taller species-rich vegetation on metalliferous spoil. Formerly it was more common but is now officially a ‘scarce plant’ and listed as ‘vulnerable’ on the Red List for England.

Flowers are scentless, 12-20 mm across, often with white spots and usually solitary. Image: Chris Jeffree.

The BSBI distribution map shown below demonstrates the loss. In this map the pale colours are records from previous decades. Maiden Pink is readily available to gardeners; therefore some of the records from the wild may be garden escapes; moreover there have been several licenced ‘reintroductions’ in an attempt to restore the species. Notwithstanding these additions, it is declining. This is alarming as the plant is regarded as one of the Britain’s more attractive native wildflowers. It is especially scarce in the south-east of England, perhaps because its sites have been claimed by developers for houses and roads, or brought into intensive cultivation as farmland.

D. deltoides, Maiden Pink, distribution map from BSBI/Maps. Note a scarcity in the wetter (western) regions, and the large number of southern sites where the species has not been seen in recent years.

Maiden Pink may be sensitive to grazing, both over-grazing and under-grazing (Godefroid et al. 2011), and it may also have been swamped by the more aggressive species that have been growing faster and taller throughout Britain and across the whole of Europe as a result of deposition of NO_x and NH₄ from the atmosphere, a kind of ‘free fertilizer’ derived mostly from vehicle emissions and agriculture. The deposition rate is well over 100 tonnes of N per hectare averaged over the entire area of Scotland, similar to the amount of N-fertilizer that farmers put on arable fields. No wonder natural plant communities are changing.

Maiden Pink grows in loosely tufted clumps like this one, only rarely with tall-growing species. Location: Dunsapie Loch, Holyrood Park, Edinburgh. Image: Chris Jeffree.

Maiden Pink is less fussy in the east of North America, where it was introduced in the 1880s. There it is found on man-made and disturbed habitats, meadows and fields; it has even been used as a component of green roofs as it is relatively drought tolerant.

Early records from Midlothian were reviewed by Barbara Sumner in her Rare Plant Register. One way to track the decline of a species is to look at old Floras. So I turned to Sonntag’s Pocket Flora of Edinburgh and the Surrounding District published in 1894. He reports that Maiden Pink is found in dry hilly pastures and gives specific locations as Arthur’s Seat, Blackford Hill, Pentland Hills, Ochil Hills, North Berwick Law, Lomond Hills, Glen Farg, Kennoway. Another local Flora, The Field Club Flora of the Lothians (Martin 1934) lists Dunglass, East Linton, Traprain, Berwick Law, Dirleton, Arthur’s Seat, Blackford Hill, Craiglockhart, Niddrie Castle. The impression I have from these lists is that Maiden Pink was a plant that one might easily have found in former times during a walk in the hills of eastern Scotland.

The typical flower colour is rose-red but horticultural varieties may differ, and sometimes white flowers have been reported in the wild. Image: Chris Jeffree.

Then I examined the modern BSBI records for the Lothians (from 1934 onwards). I was pleased to see that most of the older locations have been confirmed: there are 256 records from over 50 sites. Of course, the BSBI recorders will have scrupulously searched the locations of older records, whereas the naturalist-botanists of previous centuries had little to guide them (the UK’s OS Grid system dates from 1936). Many simply went rambling with friends to look for wild flowers whilst the ‘professionals’ reported observations to colleagues at meetings of Learned Societies and published their findings in periodicals that have long since been discontinued (but thankfully still available on-line as faithful digital copies of their yellowed pages).

The first record of the species in Britain was by Gerard. In his 1597 Herbal he wrote:

“There is a Wilde Creeping Pinke, which groweth in our pastures neere about London, and other places, but especially in the great field next to Deptford…which hath many small and tender leaves, shorter than any of the other wilde Pinkes; set upon little tender stalks, which lie flat upon the ground, taking holde of the same in sundrie places, whereby it greatly increaseth; whereupon doth grow little reddish flowers. The roote is small, tough, and long lasting.”

He called it the Deptford Pink. Later, Thomas Johnson (born around 1600 died 1644, botanist, soldier and apothecary, and known as “the father of British field botany”) revised Gerard’s herbal in an attempt to correct errors (for the new 1633 edition) but he inserted an illustration of a different pink, Dianthus armeria. This was a mistake, but as a result the plant we know as Dianthus armeria became known as Deptford Pink even though it was not the one Gerard knew from Deptford. However, the name stuck (the Deptford Pink is a rare plant with a declining southern distribution).

Leaves of vegetative shoots are linear, 8-20 mm long and up to 4 mm wide, somewhat glaucous with a waxy surface (hence the globose water droplets, as in a water-lily). Image: Chris Jeffree.

The story of the confused plant names is told in more detail by Britten (1892). His article was published in a long-discontinued journal, the Journal of Botany. It can be found on-line at the Biodiversity Heritage Library.

If you are interested in these two somewhat similar species you may read more here and here. The differences include: Dianthus armeria is an annual plant (sometimes biennial), the flowers are in clusters surrounded by an involucre of hairy leaf-like bracts and all stems produce flowers. Dianthus deltoides is a perennial, and its flowers are never in clusters (often solitary, on stalks). Only some of the stems bear flowers.

What can be done to rescue species that are on the brink of extinction? There have been projects aimed at reintroducing species to the places where they once grew. There is a Species Action Plan for Dianthus deltoides, under which plantings were carried out at five sites in Holyrood Park in September 2013. Does intervention work? The article by Godefroid et al (2011) shows that quite often introduced plants dwindle after two years, failing to reproduce themselves. This is unsurprising as the environment of the site will have changed – perhaps as a result of climate warming or (more likely) changes in grazing regime or increases in N-deposition.

We are in the midst of a global biodiversity crisis. It is vital to record gains and losses of species, and to show evidence of species losses at every opportunity. In case you haven’t seen the recent data summarising the decline in British plant species since the 1950s, you can find it here. Tracking the change in species is a gargantuan task, based on field observations by dedicated volunteer recorders over the decades. The main headline of the report is that about half of all native species in Scotland have suffered declines, although neophytes have increased.

Two current sites of Maiden Pink at Holyrood Park, Edinburgh. Above, basaltic crags above Dunsapie Loch, below, Haggis Knowe. Photos: Dunsappie Loch, Chris Jeffree; Haggis Knowe, John Grace.

The global distribution shows that the species can tolerate a surprisingly wide range of climatic conditions, with a northern limit well beyond the arctic circle, extending south to mediterranean regions. I wonder whether the species is the same genotype everywhere? The horticultural cultivars look quite different and some of those may have been the ones taken to gardens in North America, Australia and New Zealand.

Maiden Pink, global distribution according to GBIF.

It was from a New Zealand source that I discovered the explanation of the Latin name. dianthus: From the Greek dios ‘god’ or ‘divine’ and anthos ‘flower, the divine flower; deltoides: from the Greek ‘delta’ the third letter of the alphabet and referring to three-sided shapes such as triangular or delta-shaped.

References

Braithwaite ME (1994) Dianthus deltoides L. In Stewart A et al (1994) Scarce Plants in Britain. JNCC, London.

Sonntag CO (1894) A Pocket flora of Edinburgh and the Surrounding District. Williams and Norgate, London.

Martin IH (1934) The Field-club Flora of the Lothians. Blackwood, Edinburgh and London.

Godefroid S et al (2011) How successful are plant species reintroductions? Biodiversity and Conservation. 144, 672–682.