A tweet this morning from Chris Howell at Birmingham Botanical Garden reminded me that for some time I’ve been meaning to post up images of an enigmatic flower that has intrigued me for over a decade, ever since I encountered it in the Palm House at Kew.
It was the smell that I first noticed: strong and pungent like a ripe blue cheese, or unwashed feet. This drew me to a small, evergreen shrub with the wonderfully eliding name of Deherainia smaragdina, a Mexican member of the primula family (Primulaceae) though older sources put it in the Theophrastaceae, a family no longer recognised by most botanists.
At first I couldn’t spot where the smell was coming from, then I saw the flowers: larger than I was expecting (a couple of centimetres across) given that they were not immediately obvious, and very waxy and stiff to the touch. In fact (to the human eye) it was quite well camouflaged against the plant’s own leaves, not at all what one expects from a flower. However camouflaged flowers that rely only on scent for attracting insects are not unknown in the plant kingdom, and probably under-recorded: see for example Adam Shuttleworth and Steve Johnson’s work on wasp-pollinated flowers of asclepiads (Apocynaceae) in South Africa, where the “cryptic colouring” is similar in reflectance to the background vegetation. “Smaragdine” means emerald-like, so a very fitting species name.
The scent tends to come and go, perhaps affected by temperature or light levels. Under the scanning electron microscope the surface of the petals has some intriguing bulbous cells (which I’d hypothesise produce the scent) and the wavy, waxy covering of the cuticle is clearly visible:
Another intriguing thing about Deherainia smaragdina is that the bisexual flowers are in a male phase when they first open, moving into female phase only after a day or two. Compare the two flowers below. In the male phase (left) the pollen-bearing stamens are centered in the flower, hiding the female stigma (which is probably not receptive at this stage); over time the stamens move outwards to expose the stigma and the flower goes into female phase (the flower on the right):
Why this plant should smell of cheese is a mystery, but it’s probably attracting a particular type of pollinator – though what they are no one knows ! It’s never been studied, as far as I’m aware. We might predict from the scent that it’s flies, but I think that wasps are also a possibility. If anyone is doing field work in the parts of Mexico where this plant grows, please look out for it and try to photograph flower visitors: I’d love to hear from you!