Hampshire botanist Tristan Norton has found three species of star-thistle in Hampshire; all are alien plants, one is nationally Endangered and one is new to the county, with only a handful of prior records across the UK.
Tristan, who is the Botanical Society of Britain and Ireland County Recorder for Hampshire, and his friend Gavin Maclean, were plant hunting in the Test Valley, near the village of Michelmersh. Their hunt was triggered by an alert from a butterfly recorder who, while carrying out a survey for Clouded Yellow butterflies in an arable field full of Lucerne, growing as a commercial crop, had spotted an unfamiliar plant which looked like one of the star-thistles. There are several species of star-thistle and none is particularly common, so Tristan’s interest was piqued.
Tristan said: “Upon arriving at the site, we almost immediately noted a fine flowering specimen of Yellow Star-thistle (Centaurea solstitialis): with its lemon-curd-coloured flowers, silvery-grey foliage, and spiky, bushy appearance, it’s a plant that demands attention. We found about ten plants across the site and this was the first record of this species in South Hampshire since 1961”.
Red Star-thistle (Centaurea calcitrapa). Photo: Tristan NortonNext, Tristan and Gavin came upon two specimens of Red Star-thistle (Centaurea calcitrapa) which, like the Yellow star-thistle, is a species of southern and south-eastern Europe, North Africa and the Near East. Red star-thistle is classified as Endangered on both the England Red List and the GB Red List. Tristan said “There is one longstanding population in East Sussex which is regarded as probably native and in South Hampshire there are 19 prior records, the first from 1842 and the most recent from 1984”.
He continued “While admiring one specimen of the Red Star-thistle, we noticed that there appeared to be two different growth forms; one with rather aggressive thorny heads likely to pierce your shoe and another with a rather delicate, many-branched growth. After initial confusion, it soon became apparent that we had two completely different species growing side-by-side and intertwined. This second species was found to match Diffuse, or Small-flowered, Star-thistle (Centaurea diffusa), a plant native to southern and south-eastern Europe as well as the Caucasus and Türkiye. This was the first ever record of this species anywhere in Hampshire and there are only ten prior records across the UK, the earliest from Cornwall in 1888, and most of the others from Grimsby docks in the 1950s.”
If it hadn’t been for an eagle-eyed butterfly hunter and an inquisitive botanist, we might never have known about not one but three species of alien star-thistles, each one rarer than the last, and all growing happily in a field in Hampshire. Presumably they came in with the Lucerne seeds. Who knows how many other (attractive and non-invasive) aliens may be reaching our shores by a similar route?
Diffuse Star-thistle (Centaurea diffusa). Photo: Tristan NortonENDS