Geum rivale L., Water Avens

Account Summary

Growth form and preferred habitats

Like the closely related, but considerably more common and widespread G. urbanum (Wood Avens), this is a perennial species of mildly acid to calcareous, moderately fertile soils. In comparison with the latter, it prefers, or rather it much better tolerates, wetter, slower draining, ± permanently damp growing conditions. In the damp, cool oceanic climate of Fermanagh, the environmental requirements of G. rivale are readily met in a wide variety of habitats, including the damper flushed parts of deciduous woodlands, in marshy grasslands or fen-carr scrub by lakes, turloughs (so-called "vanishing lakes" with no proper inflow and outflow) and rivers, or on shady, ledges on north-facing cliffs where water seeps down them.

G. rivale persists in much wetter soils and in more upland sites than G. urbanum, including ground that floods and becomes waterlogged for periods in winter or after heavy rainfall. This is largely thanks to its well-developed, much branched, horizontally spreading rhizome-like caudex, a feature represented only by a very short thickened organ in G. urbanum (Taylor 1997b). In morphological terms, the caudex is an aggregation of leaf bases with their associated dormant buds and it is seen as intermediate between a true rhizome and an over-ground stem or stolon. The caudex of G. rivale is very well developed and it can grow and spread over a considerable horizontal distance.

Survival of G. rivale in waterlogged conditions is due to the numerous vigorous adventitious roots the caudex produces (Waldren et al. 1987). Since it simultaneously develops annual flowering shoots, the horizontal stem can rot away at one end, extend at the other, produce a dense clone and under favourable growing conditions persist for many years (Taylor 1997b).

Fermanagh occurrence

G. rivale is frequent in Fermanagh, having records in 148 tetrads, 28% of those in the VC. As the tetrad distribution map shows, it is widely scattered but much more frequent in the damp uplands to the SW of Lough Erne.

Considering the amount of wet ground that exists in Fermanagh, it is rather surprising that Water Avens is less than half as frequent and widespread in the VC in comparison with Wood Avens. Of the two, G. rivale is somewhat more competitive in grassland situations, slightly more tolerant of occasional mowing (for example, on verges or waterside banks) and, likewise, with respect to light grazing of pastures (Sinker et al. 1985). On the other hand, Water Avens does not colonise the numerous weedy or dry soil situations exploited by G. urbanum.

Another aspect of competition affecting G. rivale is that when aggression is sufficiently strong to limit the species' growth and resources, maturity of the plant measured in terms of first ability to flower can be delayed for some years. The species is polycarpic and individual plants continue to flower and fruit for a number of years after attaining maturity, so that the loss of two or more years' seed output may be but a small percentage of the total seed production throughout life. Nevertheless, the prolongation of the juvenile phase greatly increases the risk of mortality prior to reproduction and this will inevitably affect the survival capacity of the population in a particular community (Salisbury 1942, p. 54).

Vegetative reproduction

Reproductive strategy in G. rivale is a combination of vegetative and sexual, weighted towards the former strategy. Consequently, G. rivale is able to compete directly with neighbours, or when they are more vigorous, it can avoid competition for ecological space through the mobility conferred upon the species by its vegetative dispersal, a property also displayed by the related stoloniferous species Potentilla anserina (Sliverweed) and P. reptans (Creeping Cinquefoil) (Erikkson 1986).

Flowering reproduction

Pendulous, bell-like (campanulate) pink to dark crimson, 5-merous flowers are produced in a 2-5 flowered narrow cyme from late May to September. The flowers are protogynous, the stigmas ripen first, protruding beyond the immature anthers, inviting cross-pollination by bees, flies or beetles attracted by semi-concealed nectar, secreted by the saucer-shaped hypanthium at the base of the stamen filaments. Secondarily, after the anthers have matured and their filaments elongated, automatic self-pollination becomes a possibility (Taylor 1997b).

Either way, after pollen-transfer and fertilisation, around 100-150 crowded achenes are produced per flower, each one equipped with a strong hooked awn developed from the original stigma, enabling it to adhere to the coat of a passing animal or human (Ridley 1930, p. 142). A Swedish study found that G. rivale achenes attached easily to the fur of both fallow deer and domestic cattle and had the potential to be transported from tens of metres up to a kilometre or more, depending upon the range of the animal species and the amount of grooming it performs (Kiviniemi 1996). The seed appears to be transient in the soil, persisting for less than one year (Thompson et al. 1997). Presumably the seed germinates in spring after overwintering, although nothing appears to be known about field germination and seedling establishment (Taylor 1997b).

Variation

A taller variant of the plant with stems up to 30(-50) cm, with more coarsely toothed leaflets and flowers with initially white petals that later turn somewhat pinkish, occurs in northern regions including Iceland, the Faeroes, N Scandinavia, N America and Britain. It has been variously named f. subalpinum, var. subalpinum or subsp. subalpinum (Neumann) Selander. In Britain, it has been recognised as the latter by Sell & Murrell (2014).

British and Irish occurrence

Water Avens is widespread in both B & I, but has a definite northern bias, especially noticeable in Ireland. There is also a much lesser western leaning in its distribution in England, and it is widespread throughout Wales (Preston et al. 2002). Being a species of wetter ground, G. rivale has suffered a decline in its presence in both islands due to drainage associated with the intensification of agriculture during the last 60 years or so. This change in land management and species loss is particularly marked in C & S England. The plant is also grown in gardens and occasionally escapes (D.J. McCosh, in: Preston et al. 2002).

The Fermanagh data are insufficiently detailed historically to allow any estimate the local extent of this general trend in losses.

European and world occurrence

G. rivale occurs throughout most of W, N & C Europe but thins markedly southwards in France, Spain, Italy and the Balkans. It is entirely absent from the Mediterranean isles and Macronesia and becomes scattered, and perhaps less well recorded, eastwards into Russia, the Caucasus, Turkey and Siberia (Kurtto et al. 2004, Map 3374). Although it is not circumpolar, the native range of G. rivale is amphi-atlantic extending to N America, from Newfoundland to British Columbia, Colorado and New Jersey (Sell & Murrell 2014; Hultén & Fries 1986, Map 1091).

Threats

None.

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