Parthenocissus ‘Fenway Park’ – the original plant
What, exactly, is an heirloom?

A new weed evolves

peppered moth,evolution,birch,black,white. Image ©Martinowksy. Distributed under the GNU Free Documentation License How often is it that you see natural selection happening before your very eyes? Well, it’s been happening at the Royal Horticultural Society’s Garden at Wisley, just south of London, where a weed has evolved which is less likely to be pulled out by the gardeners!

It’s like the moths in the old industrial north of England. For centuries, the white form of the peppered moth had been the most common, camouflaged against the pale bark of birch trees upon which the moths rested. Then, as industrial pollution grew, the bark became covered in soot and the white moths became highly visible and were snapped up by birds. (Click the image, left, to see white and black forms on birch bark.) The less common black form then became much more common. More recently, as the air became cleaner again, the white form has enjoyed a resurgence.

At Wisley, annual meadow grass (Poa annua) is a persistent weed but the gardeners are diligent in rooting it out and consigning it to the compost  heap. But over the years forms with darker stems and leaves have developed – colours which show up less well against the dark soil and which are less likely to be noticed and pulled or hoed off by gardeners. poa annua,purple,Wisley,evolution. Image © (all rights reserved) The result has been the development of a distinct brownish purple leaved form known not seen anywhere else. Known as Poa annua f. purpurea, it was first formally described in 2003. Click on the image, left, to see how well camouflaged the purple form is.

On the Rock Garden and on the Portsmouth Field (the trials field) at Wisley this new “invisible” form has become a particular problem, especially now that less chemical weed control is used and control depends more on the gardeners’ sharp eyes. I only noticed the plant in the picture when I bent down to pick up my glasses!


Feed You can follow this conversation by subscribing to the comment feed for this post.

Mike Grant

Hey, it's great to see "my" weed get the publicity it deserves!!!


Interesting. This is a strange weed--I think they use it here for golf greens. They plant something else expecting it to be overtaken in a few years by annual bluegrass (same weed, different common name).

Graham Rice

For those who didn't click on the "first formally described in 2003' link in the piece - Mike Grant, who refers to "my" weed, is the botanist who published the formal description.

Interesting that something like this is used on golf greens - I would have thought it pretty tough to get rid of once it's there.

Jim Fox

The same thing here in Seattle, WA, with shotweed - an annual cardamine (forgive me for not having the botanical name in front of me). In the nursery, we use crushed gravels for the walks. As we've cut back on herbicides and do more hand weeding, the shotweed, in ten years time, produces more and more smaller, prostrate, purple, brown, or otherwise darkened plants to match the color of the gravel and the soils in the pots, and the crevices in the gravel. Fascinating to watch. Who knew it was such an intelligent weed.
Jim Fox

Graham Rice

Thanks, Jim, that's fascinating. Shotweed is Cardamine oligosperma - and I understand that it's edible so after pulling it actually has a use!

It looks pretty much the same as the European hairy bitter cress, Cardamine hirsuta, which is a menace on nurseries. I know one nurseryman who carries a plastic bag with him at all times and whenever he see the weed he pulls it and bags it. When it's full, the bag is tied and goes in the trash.

Jordan 1

And scientists concerned about climate change believe it will cause more drought in many areas in the future.

The comments to this entry are closed.