Geum rivale – May 19th 2025 – Water Avens

If plants had psychological characteristics, this species would be classed as an introvert because its flowers look down to the ground whereas those of its extrovert close-relative Geum urbanum always face up. Does this mean G. rivale is not attractive to insect pollinators who might fly straight past without noticing it?  I don’t know the answer to this question, but G. rivale is said to be pollinated by bees in search of a good supply of nectar, especially Bombus hortorum and Apis mellifera,

General features: flowers are nodding and few, calyx purple, sepals triangular, petals 1-1.5 cm, dull orange-pink. Somewhat hairy all over. Image: Chris Jeffree.

Geum rivale is found throughout Great Britain but is less common in the south. Likewise, in Ireland the species is rarer in the south. It isn’t clear why this may be, but we may speculate somewhat as follows. We know that the species is intolerant of grazing and drought, and in Europe it does not extend to the warmer parts of the Mediterranean countries. The clue is in the England name, Water Avens. It likes wetter places and is often by rivers, streams and ditches. According to the BSBI it is “A perennial herb of mildly acidic to calcareous, slow-draining or wet soils, in shaded or open habitats, including by canals, stream-sides and flushes in deciduous woodland, carr, herb-rich hay meadows and montane willow scrub and tall-herb communities on ledges”. The distribution seems to be controlled by soil moisture, although its near-absence in the extreme west (Cornwall, Hebrides, West of Ireland) remains a mystery.

Detail of flower. Image: Chris Jeffree.

The plant is a perennial belonging to the rose Family, Rosaceae, native to the British Isles and much of Europe. It has a well-developed rhizome system acting as an over-wintering food store and enabling rapid spring growth and vegetative expansion. From the rhizomes it forms new rosettes of leaves every year, and makes wiry stems up to 60 cm tall, bearing flowers in May.

The flowers are fairly typical of the rose family (see the images). Stigmas ripen before the anthers and so cross-pollination is encouraged. This contrasts with G. urbanum, where self-pollination is usual and cross-pollination rare. The fruit is an achene with a strong hooked appendage for dispersal on the fur and clothing of passing animals and humans.

Flower cut away to reveal receptacle bearing the many carpels with their hairy stigmata. The anthers are yellow. The hermaphrodite flowers are protogynous (female parts mature first). Here, the mature stigmas are projecting beyond the still unripe anthers, so that at this stage cross-pollination can result from insect visits. Later the stamens elongate, bringing the pollen-covered anthers to the level of the outer stigmata, so that when the flower closes automatic self-pollination is readily affected (Taylor 1997). Image and sample preparation: Chris Jeffree.

Sometimes G. rivale and G. urbanum grow together; when this happens, hybridisation is highly likely, although the flowering periods are somewhat different (G. urbanum is later). The formation of hybrids between these two species was recorded in France over 100 years ago, and the hybrids were then called Geum rivali-urbanum. Those who read French may like to look at this old paper, easily viewed on the internet. Stace (2019) lists the hybrid as G. x intermedium, saying “in all respects intermediate and highly fertile, forming a complete spectrum between the parents”.

From Richard Abbott’s blog, May 2020. Hybrid swarm of Geum rivale (Water avens) and G. urbanum (Wood avens) along a roadside near St Andrews, Fife, on 21 May, 2020. Inset: Closeups of flowers (not to scale) of G. rivale (left), G. urbanum (right) and their hybrid (centre). Only one individual of G. urbanum was flowering on the day the photo was taken, while hundreds of the earlier flowering G. rivale and scores of hybrids were in flower. Photos (R. J. Abbott)

However, despite the appearance of a ‘complete spectrum’ (sometimes called a ‘hybrid swarm’), recent research suggests something simpler. There may be only four genetic types: the two parents, their F1 hybrid and backcrossed offspring F1 x G. rivale. Any other hybrids (i.e. hybrids of hybrids) do not survive to adulthood. The phenomenon was well-described in one of our first Botanical Society blogs written by our colleague Richard Abbott (sadly, no longer with us). He and his Edinburgh colleagues published several articles on the subject (listed below). It is suggested that the two species diverged from a common stock  2-3 million years ago, perhaps becoming isolated from each other by their contrasting habitats (wet versus dry). In modern times, habitats became more fragmented and the chance of the two species meeting was therefore increased.

Distribution of G. rivale, G. urbanum and their hybrid, according to BSBI records. The hybrids are mostly found where the ranges of the parent species overlap.

There is a third species, an alien from North America resembling Geum urbanum. That one, G. macrophyllum, has been seen many times in Edinburgh (Chamberlain and Jeffree 2024 and here). It has been spreading fast in the last few years (or perhaps it has been mistakenly recorded as G. urbanum). There are a just a few records of its hybridisation with Geum urbanum, but none with G. rivale.

Gardeners often grow Geums but not the native ones. Many garden varieties have red flowers and are descendants of G. chiloense, originating on Chiloé Island in southern Chile. This species was introduced to Britain in 1824, and the well-known double variety is called Mrs Bradshaw.

As for the names of Avens and Geum rivale: Avens is Latinized Greek for “taste” referencing the roots of the plant which have been compared to chocolate flavour (please don’t try tasting them). Concerning the name Geum, my AI prompt says: “The botanical name Geum (pronounced JEE-um) derives from the Greek word ‘geno’ meaning to yield or to produce.  This is a reference to the plant’s root, which, when freshly dug, has a clove-like aroma or fragrance. This aroma led to other names for the plant, such as Radix caryophylata (Clove Root) and its corruption, Gariophilata”.

References consulted

Chamberlain M  and Jeffree C (2024) Geum macrophyllum. An alien that is spreading. BSS News, 123, 23-25.

Jordan CY, Lohse K, Turner F, Thomson M, Gharbi K, Ennos RA (2018) Maintaining their genetic distance: Little evidence for introgression between widely hybridizing species of Geum with contrasting mating systems. Molecular Ecology 27, 1214-1228.

Roze ME (1896) Le Geum rivali-urbanum. Bulletin de la Société Botanique de France 43, 273-279.

Ruhsam M, Hollingsworth PM, Ennos RA (2011) Early evolution in a hybrid swarm between crossing and selfing lineages of Geum. Heredity 107, 246-255. View this at https://www.nature.com/articles/hdy20119.pdf 

Ruhsam M, Hollingsworth PM, Ennos RA (2013) Patterns of mating, generation of diversity, and fitness of offspring in a Geum hybrid swarm. Evolution 67, 2728-2740.

Stace CA (2019) New Flora of the British Isles. 4th edition. C&A Floristics.

Taylor K (1997). Geum rivale L. Journal of Ecology, 85, 721-731.

Waldren S, Etherington JR,  Davies M S (1989). Hybridization and ecology of Geum rivale L. and Geum urbanum L.(Rosaceae) at Malham Tarn, Yorkshire. Botanical journal of the Linnean Society, 101, 199-211.

©John Grace