Geum urbanum L., Wood Avens

Account Summary

Growth form and preferred habitats

This variable, wintergreen, rosette-forming, pubescent, herbaceous perennial possesses a short, thick, overwintering rhizome that seldom branches. A new rosette of basal leaves is produced by the rhizome apex each year, but the lifespan of individual rhizomes is only a few years (Taylor 1997a). G. urbanum relies on seed to disperse and colonise suitable new ground and therefore is usually sparsely distributed in most sites, since it originates from widely scattered propagules and possesses little capacity for vegetative spread (Grime et al. 1988). Wood Avens occurs in full- or semi-shade and shelter of almost every small or large patch of deciduous woodland, scrub and substantial hedge in Co Fermanagh. Individual plants are also frequent as sporadic weeds of fully-lit, fairly disturbed, open ground in gardens, urban waste ground and in neglected corners in quarries and similar unmanaged rural situations.

The species shows a definite preference for mildly acid to calcareous, sloping, free draining, moist soils in the pH range 5.4-7.7 that are average in terms of plant nutrients and fertility. It possibly benefits in habitats with a modicum of additional nitrogen, but it is not a strong plant competitor as such, being more of an environmental stress tolerator (Ellenberg 1988; Grime et al. 1988). As such it cannot compete in grassland communities and is virtually absent in grazed habitats (Taylor 1997a). G. urbanum can tolerate summer drought conditions rather well in some calcareous habitats in S England, although similar conditions would be most unusual in NI with its frequent damp periods and strongly expressed Western Atlantic climate. Having said this, Wood Avens can be considered a moist site indicator, being absent both from places that dry out and from wet ground (Taylor 1997a).

Fermanagh occurrence

Since its ecological requirements are readily met in Fermanagh, Wood Avens is regularly recorded in 332 tetrads, 62.9% of those in the VC. It is absent mainly from strongly acid soils, wetlands, closed turf grasslands, more exposed uplands and regularly grazed ground (Taylor 1997a). While generally a lowland species, the plant is hardy and easily survives the mild winters in our oceanic area, the wintergreen rosette probably being physiologically active right throughout the year. Perhaps on account of its ability to persist in some types of disturbed site, G. urbanum is more than twice as frequent and widespread as G. rivale (Water Avens) in Fermanagh.

It is not easy to establish the upper altitudinal limit from the local Fermanagh data, but it is probably somewhere around 350 m on the Belmore limestones, while the highest recorded site in B & I is 512 m in the English Lake District (Wilson 1949).

Flowering reproduction

Flowering takes place from June to August, the inflorescence consisting of only 2-5 flowers borne on a 90 cm tall stem that waves its relatively small (10-15 mm) yellow blossom to attract a range of insects, mainly flies, offering food rewards of little nectar but plentiful pollen. Despite this effort, most flowers are probably unvisited and, in this event, they are automatically selfed (Taylor 1997a). Each flower contains around 20 carpels.

In addition to the normal summer flowering, very tiny flowers are produced on side branches in September, when the fruits of the topmost heads are already well on the way to producing seed (actually achenes are single-seeded dry fruits).

Fruiting heads consist of brown, burr-like clusters of achenes, each with a 6 mm long, hooked awn which readily attaches to the coats and fur of passing animals and disperses the seed (Ridley 1930, p. 142; Hutchinson 1972).

Seed survival in soil is, at best, short-term persistent (1-5 years), although other studies suggest it is transient (less than one year) (Thompson et al. 1997). In one English outdoor, pot-based study, after a cold spell of weather germination began in December, reached a peak in March and ceased at the end of May. A few additional seedlings appeared in the following spring (Roberts 1986).

British and Irish occurrence

The New Atlas hectad map indicates that the distribution of G. urbanum is widespread and stable throughout B & I, but it becomes rare or absent in NW & C Scotland including Orkney, Shetland and the Outer Hebrides. It is also rare or absent on the ± permanently wet, strongly acidic peats of W Ireland. However, the distribution does indicate that G. urbanum has a very wide climatic tolerance (Taylor 1997a).

European and world occurrence

G. urbanum does not occur in Iceland and the extreme N of Europe, but it is widely distributed southwards from S Scandinavia and Russia (65°N) to the Mediterranean, where it thins out in southern parts of Spain, Portugal and Greece. It is well represented in Corsica, Sardinia and Sicily, but absent from all the other Mediterranean isles and from the Macaronesia islands (Kurtto et al. 2004, Map 3379).

Beyond Europe, G. urbanum extends eastwards to W Asia, W Siberia and the Himalaya and it is also common on the NW African coast from W Algiers to the Tunisian border (Hultén & Fries 1986, Map 1092; Taylor 1997a). It has been introduced, presumably accidentally and to a minor degree, in eastern N America and New Zealand (Hultén & Fries 1986). In New Zealand, it is easily confused with the similar and more common introduction G. alepicum Jacq., so that G. urbanum may be overlooked to some extent and perhaps is more common than imagined (Webb et al. 1988, p. 1082).

Threats

None.

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