Submitted by AJ Cann on Wed, 10/07/2024 - 09:01

White Thistles

Creeping Thistles are just coming into flower, but among their number there are some pale white ghosts. More...

Creeping Thistles, Cirsium arvense, is much maligned and hated by some as a feared agricultural weed, but it has great wildlife value. Its abundant nectar attracts clouds of insects - if you find some in flower, sniff and enjoy the beautiful honey scent which pulls in an array of pollinators. It also houses its own little ecosystem of bugs, flies, moths and weevils which depend on it and feed on nothing else. In addition to this range of insects, Creeping Thistles are also home to microscopic house guests including bacteria, fungi and viruses. Some of these associations are obvious, such as Creeping Thistle Rust but others have no outward sign. Occasionally you may come across thistles with ghostly white tips, which, given how much this plant is hated, I have always assumed was herbicide damage. In fact it turns out that this is the result of a bacterial infection with Pseudomonas syringiae. Unlike most bacteria, the symptoms of "white‐colour disease of thistle" are very characteristic and affected plants can be identified easily by eye from some distance. 

White Thistles

So whether you hate this plant or marvel at its ability to support life, keep an eye out for white thistles and amaze your friends with your microbiological knowledge. 

See: The Mystery of the "White" Thistles:

Photos: Sue