Silverweed was one of the first plants I ever knew, as it was common alongside the road in the village where I grew up. Some friends thought it was a buttercup, but I had the Observer’s Book of Wild Flowers and I knew better. Its leaves looked silver and were silky to touch.
19th Century portrait of Silverweed. Note the tap-roots, often harvested for food. Original book source: Prof. Dr. Otto Wilhelm Thomé Flora von Deutschland, Österreich und der Schweiz 1885, Gera, Germany. Permission granted to use under GFDL by Kurt Stueber.
It’s a widespread plant in Britain and Ireland, but not exactly ‘common’. It occurs in most of the 10 km squares shown on the BSBI’s distribution maps, but finding it can take some time. In Scotland, I see it mostly at the sides of roads, on waste ground and on shorelines. In his 1597 herbal John Gerard says “It groweth in moist places near unto highways and running brooks everywhere”. It has a degree of salt tolerance, accounting for its presence on coastal dunes and along salted roads.
P. anserina at the edge of an abandoned road showing the extension of stolons (up to about 1 metre). Photo: John Grace.
Potentilla anserina belongs to the rose Family, Rosaceae, and it is a native plant producing long creeping stolons, just as strawberry does. The pinnate leaves are usually densely hairy (more hairs on the lower surface) and can appear silver, hence its English name. Early work in Britain showed the species to be highly variable (Ockendon and Walters 1970), and some authors consider the species to be an aggregate with named subspecies, microspecies or even completely different species. For example, when I went to the website of the Global Biodiversity Information Facility (GBIF) I wondered why Potentilla anserina was frequent in Australia but completely absent from New Zealand. Later, I realised that the New Zealand plant is called P. anserinoides. I looked at some on-line herbarium specimens from the Auckland Museum and saw that their plant does indeed look different from the one we know in Europe, with somewhat straggly leaves. But one herbarium specimen from the Royal Botanic Gardens of Sydney (Australia), labelled Potentilla anserina (from 1891) looks much the same as the Auckland plant.
Flowers appear from June to September. Photo: John Grace. You will enjoy images of the flower in ultraviolet, as seen by a bee.
The remarkable feature of this species is that it is native throughout the northern hemisphere, and stretches from arctic to almost-subtropical latitudes. This is unusual; in most of the northern hemisphere, species are either native to the Old World or the New World. With such a very wide geographic distribution it is not surprising that considerable variation exists. Many years ago, Rousi (1965) embarked on a thorough comparison between the reproductive behaviour and morphology of Silverweed samples collected in California and Finland, growning them together in Finland. Everywhere, plants were of two sorts according to their chromosome counts, most being tetraploid (2n = 28) but a few were hexaploid (2n = 42). We see the same variation in chromosome counts in Britain, but the two types look much the same. Rousi (1965) found the hexaploid types had infertile pollen and no seed.
Silhouettes of representative plants from different parts of the world, grown in a common garden in Finland, compiled from Rousi (1965) Annales Botanici Fennici 2, 47–112. A: Marlborough, New Zealand; B: Montaca, California, USA; C: Karuna, Finland.
Adding to the taxonomic confusion, I was surprised to see that some botanists insist on calling Silverweed Argentina anserina (Soják 2010). Around 70 related species were moved from Potentilla to Argentina by Soják’. The genus name Argentina is a very old one, even mentioned in Gerard’s herbal; now it has been resurrected. But Stace, in his New Flora of the British Isles, steadfastly keeps Silverweed as Potentilla anserina.
Flowers are borne singly on slender stalks up to 25 cm, and are never very numerous. Photo: John Grace.
Worldwide there are at least 300 generally-accepted species of Potentilla, and their evolutionary relatedness has been investigated by modern methods of numerical taxonomy based on DNA similarities. In one study, Silverweed and three other species are quite different from the rest of the Potentilla genus (Töpel et al 2011) adding weight to the argument for calling them something else (i.e. Argentina). But the authors prefer not to make such a strong recommendation, saying that it may be “more reasonable” to keep Potentilla intact “in order to minimise name changes”.
Ove Eriksson of the University of Stockholm has written much about the population dynamics of the species (eg Eriksson 1986). At a seashore meadow he found that vegetative spread (via stolons) dominated recruitment to the population although seedlings were present too. Daughter plantlets (‘ramets’) often flowered within a year whilst seedlings took 4 years. The turnover rate of the population was estimated as over 30 years. Erikson was also interested in the status of the species in Canada, where the plant is found in a range of habitats similar to those in Europe but is also a component of some natural vegetation types (see Miyanishi, Eriksson and Wein 1991).
Leaves of silverweed. The plant can form a dense canopy like this one, as a result of establishment of daughter plants (‘ramets’). Photo: John Grace.
Silverweed was a food plant in earlier times, and in some parts of the world it is still used as a food source. The long slender roots are rich in carbohydrates, perhaps almost as rich in starch as potatoes and widely used before the introduction of potatoes in 1586. Archaeobotanist Gordon Hillman of University College London has written a highly readable blog on this topic, which you can read here. His note on the use of silverweed in the Hebridean regions of Scotland goes as follows:
Silverweed has long been a medicinal plant, as noted in the Herbals of both Gerard and Culpepper. As with many herbal remedies, it seems to be good for almost all common ailments. There is much modern work, especially in China, to identify biologically active compounds from roots and leaves. In a recent review, over 200 compounds were identified from Potentilla species, many of them from P. anserina (Augustynowicz et al 2021). What is the evidence that these compounds have the potential to be used in medicine? The authors explore pharmacological properties of plant extracts and compounds; they unearth much evidence from in vitro work with cell cultures to in vivo research using mice, rats and chicks. As with much herbal medicine, what is lacking so far is clinical evidence. Without clinal evidence that a compound is both efficacious and safe, a new compound will never be considered by the UK national pharmacological ‘gatekeeper’ (the National Institute for Health and Care Excellence, known as NICE).
A taxonomic conundrum. Left: the global map of Potentilla anserina from GBIF showing no records from New Zealand. Right: P. anserinoides is recorded only in New Zealand, but is probably the same as P. anserina in Australia.
As for the origin of names, “Potentilla” comes from “potens”, Latin for powerful, perhaps via the French “potence” . “Potentilla” thus traslates as “little powerful one”. Possibly the ‘power’ implies medicinal power. “Argentina” comes from the Latin, “argentum” meaning silver, relating to the silvery leaves. The specific name “anserina” is Latin for goose, perhaps because geese like to eat Silverweed, or that someone thought the leaves looked like the feet of geese.
References
Augustynowicz D et al (2021) Recent phytochemical and pharmacological advances in the genus Potentilla L. sensu lato – An update covering the period from 2009 to 2020. Journal of Ethnopharmacology 266, 113412.
Miyanishi K et al (1991) The biology of Canadian weeds. 98. Potentilla anserina L. Canadian Journal of Plant Science 71, 791-801. https://cdnsciencepub.com/doi/10.4141/cjps91-113
Ockendon DJ and Walters SM (1970) Studies in Potentilla anserina. Watsonia,8, 135-144. https://archive.bsbi.org.uk/watsonia_8.html
Rousi A (1965) Biosystematic studies on the species aggregate Potentilla anserina L. Annales Botanici Fennici. 2, 47–112. https://www.jstor.org/stable/23724290
Soják J (2010) Argentina Hill, a genus distinct from Potentilla (Rosaceae). – Thaiszia – Journal of Botany 20, 91-97. https://www.upjs.sk/public/media/5486/091-097-sojak-upr.pdf
Töpel M et al (2011) Molecular data and ploidal levels indicate several putative allopolyploidization events in the genus Potentilla (Rosaceae). PLoS Curr. 3, RRN1237. https://wellcomeopenresearch.org/articles/8-464/v1
©John Grace
Botany in Scotland 