Nettles are characterised, amongst other things, by having flowers with a single egg in their ovary and a single stigma, the structure which conducts the pollen to its target. Work by developmental biologists almost a century ago suggested that the ancestor of nettles probably had two eggs per ovary after discovering that at a very early stage of development nettle ovaries contain two eggs one of which disappears as the flower develops resulting in the single egged flower which characterises the family. It was therefore a great surprise when plant collections from Costa Rica examined in the 1990s were found to have flowers with two or three eggs and stigmas per ovary. These very unusual plants were described as a new species: Boehmeria burgeriana by colleagues Melanie Wilmot-Dear and Ib Friis. Continue reading Ghost flowers in the nettle family
I first came across this tiny creeping herb in my garden where it had been planted as an ornamental. The bright green leaves, mostly less than 3 mm across form an attractive carpet. Until now I had never been able to spot its flowers despite having checked several times over the last few years. My guess is that this species has a relatively narrow flowering time in spring and the flowers are so tiny that they are only visible with a hand-lens. For several years the genus has intrigued me, not so much because of its small size and creeping habit but because of its distribution and evolutionary relationships.
Firstly because Soleirolia consists of a single species that in the wild is only known from the Mediterranean island of Corsica. This is the only genus of nettle I know that is restricted to a single island or to the Mediterranean and I am very keen to try and found out why this could be (the history of the Mediterranean basin is quite a turbulent one). Secondly Soleirolia has traditionally been grouped with the widespread Parietaria and intriguingly with Gesnouinia, which also includes a single species but is restricted to the Canary Islands in the Atlantic Ocean. Whilst they look very different as plants their female flowers share many similarities of form. It might be, therefore, that Soleirolia and Gesnouinia should be viewed as Parietaria species that have diverged morphologically as a consequence of being isolated on islands, a common phenomenon in evolutionary biology. I am currently testing this possibility using DNA sequence data and could have a better idea in a couple of months.