Monday, June 11, 2012
Between the Woods and the Water
There are numerous related pairs of species in the British flora that frequently form hybrids when they are within easy reach of roving pollinators. Primroses and cowslips, whose hybrid is the false oxlip are one pair of textbook examples while wood avens Geum urbanum (above) and water avens Geum rivale (below) are another. Wood avens is a plant of dry soils on woodland edges (and it's also a persistent weed in the dry soil of my garden). Water avens thrives in wetter places, like the edges of ditches.
When they're well separated the two species are quite distinct. Wood avens produces upward-facing, yellow star-shaped flowers while water avens blooms are pink and pendulous, like lamp shades.
Wherever the two grow close together they hybridise. A couple of days ago I found wood avens on the dry side of a hillside footpath and water avens growing in the ditch on the other, along with ...
..... hybrids like this, with the yellow petals of wood avens and the nodding flower shape of water avens.
Within these hybrid populations, which continue to intercross with either parent, you can find a wide range of flower form and leaf shape that's intermediate between the parents but I can't recall ever seeing upward-facing star-shaped flowers like wood avens with the pink petal colour of water avens. Maybe some combinations of characters aren't possible.....