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.....


  1. Dear Phil, I was puzzled by this post as I'd not heard of Wood Avens, and put it down to my lack of botanical knowledge and "not noticing". Today, whilst trying to sort out the ID of a Tormentil/Cinquefoil species that's appeared on the butterly bank at our local reserve ("Hang on, that's not Silverweed!"), I stumbled across the answer to the Avens conundrum. The plant that I've been referring to all my life as Herb Bennet IS Wood Avens, but only one of our numerous flower books makes the connection between the two. Successive versions of Fitter et al refer to HB, whilst other books refer to WA. Fortunately, on the page for Creeping Cinquefoil in a Collins photoguide, I spotted the HB/WA and all became clear. In this instance, a glance at the Latin name would've solved the mystery sooner, but I know that wholesale changes to genera often make this a fraught task too. Thanks for your continuing efforts to educate the hard of botanising.

  2. I guess you tend to stick with the names that you used when you first became acquainted with a plant Graeme. I do with Latin names anyway. There are a lot of plants whose Latin names have changed since I first learned them but it's the original that always sticks in my mind. Actually, I think herb bennet (a corruption of herba benedicta, the blessed herb, apparently) is a much more interesting name. I read somewhere that Neolithic graves had been found containing woven amulets made from its stems. It's a damn nuisance in my garden though - those hooky seeds get carried around all over the place.