A thistle banned as a noxious weed ranks among Britain's best nectar plants
Spear thistle is Scotland's national flower, a legally listed noxious weed in nine American states, and one of the richest nectar sources in the British countryside. That split personality runs through the whole plume thistle genus, Cirsium, which farmers fight while bumblebees, goldfinches and migrating monarchs depend on it.
Cirsium holds 493 accepted species of biennial and perennial plants in the daisy family, most native to Eurasia and northern Africa, with about 60 in North America. What sets these plume thistles apart from other thistle genera is the parachute on each seed: a tuft of feathered hairs rather than plain ones, which lets the wind carry seeds long distances. The name comes from the Greek kirsos, probably meaning swollen vein. Heads are usually purple, pink or rose, occasionally yellow or white, and bloom from April to August.
Species vary in how they defend and spread themselves. Leaves are often spiny and sometimes hairy, and the flaps running down the stem, called wings, can be bold, faint or missing altogether. Creeping thistle, native across Europe and northern Asia, spreads underground through rhizomes as well as by seed, which is one reason growers dislike it.
The case for thistles is strong. In a British survey backed by the UK Insect Pollinators Initiative, spear thistle made the top ten for nectar, and another study ranked it third for sugar per flower unit. Its seeds feed European goldfinches, and its leaves feed painted lady caterpillars. The Xerces Society promotes thistles for wildlife, pointing out that monarch butterflies fuel up on tall thistle during migration, and some American seed companies sell native thistle seed for habitat restoration.
People eat them too. Rural cooks in southern Europe have long gathered several species, Cirsium oleraceum is farmed as food in Japan and India, and Cirsium setidens appears as a vegetable in Korean cooking. In North America, where spear thistle is an introduced invader, it goes by the name bull thistle.
Source: Cirsium
