Weedy and greedy but buttercup no pain in the bum

Buttercups are usually applied to top end of the body, under the chin, to test your predilection for butter. If your neck glows yellow, butter is your thing.

While I can't explain the butter test, I can, thanks to some physicists via wired.co.uk, explain why the flowers are so reflective. It's down to a two layered upper surface on the flower, with a sliver of air between them. The yellow light is reflected by the smooth cells surfaces of both layers, and the air sliver, creating the extra lustre.

In the case of the buttercup I've illustrated here, Ranunculus ficaria (sometimes called Ficaria verna*) from the produce garden at Heidi Museum of Modern Art in Heidelberg (in August 2013), you should apply it to the rump region of your body. It's tempting to think it might be a way to see if the sun shines from there but no, it's to treat the unwanted symptoms of haemorrhoids. I'm presuming it's also a concoction from the leaves rather than the oh-so reflective flower.

The pilewort is native to much of Europe, where it is also known as the Lesser Celandine. Just to confuse things and to illustrate the benefit of scientific names, the Greater Celandine, Chelidonium majus, is a poppy relative and not in the same family as Ranunculus. The Greater Celandine is applied to warts (perhaps we should call it the Wartwort?) while the Lesser Celandine is applied to your bum, and gets called the Pilewort.

This is the warning on the Plants for a Future webpage for Ranunculus ficaria: "All parts of the plant are poisonous. The toxins are unstable and of low toxicity, they are easily destroyed by heat or by drying. The sap can cause irritation to the skin. Do not use internally. Stop using the herb if breathing problems or chest and throat tightness."

Despite being 'easily destroyed by heat or by drying', the website notes further down that 'it is not recommended for internal use because it contains several toxic chemicals'. Despite minor irritations to sensitive-skinned souls, it has been used for thousands of years to treat haemorrhoids, apparently externally (more or less).

Should you decide to grow it (for personal use only), beware. It can be quite weedy and 'greedy'! In shade it forms bulbils (at least the subspecies bulbilifer does) at the base of the leaves and, 'you would regret introducing it into your garden' says the Plants for a Future website.

There are less invasive cultivars, apparently, including some that flower (at least in Cornwall, UK) earlier in the season, before the pollinating insects are about. Like many of our native sun orchids (Thelymitra) the flowers only open on sunny days, and then only after 9 am and before 5 pm (at least in Cornwall).

In Australia, where we generally call this species Ficaria verna (*Ficaria being a genus of 5-15 species sometimes segregated from Ranunculus with its 500 or so species), the species has escaped at least once into a semi-natural area around Lake Wendouree in Ballarat. Given its weedi- and greediness, I imagine it could easily spread elsewhere.