Botany picture #31: Prunella grandiflora

Prunella grandiflora, Germany, 2004. It is fairly similar to P. vulgaris but, as the name implies, much larger in all parts including the flowers. Another difference is its clumped as opposed to long-creeping growth form, and its uppermost leaves are not directly under the inflorescence as in P. vulgaris. This is the species from which a splitter would segregate another species restricted to the Pyrenees. Prunella hastifolia, as the segregate was once called, is a bit larger-flowered even than the typical P. grandiflora and prefers different soils, but it currently only has the status of a subspecies. I don't have a picture of it, sadly.

I had grown very fond of this genus already when I was lucky enough to co-supervise a German Diplom thesis (~honours/M.Sc.) on gynodioecy in P. grandiflora. Gynodioecy means the occurrence of hermaphroditic and female individuals in the same species. See below:

The left flower is from a hermaphroditic plant and has fertile stamens, the right one is from a female plant where the flower is smaller and the stamens are underdeveloped. The puzzle is of course why a plant would do that, as it loses 50% of its reproductive potential (plus it might be less attractive to pollinators because the flower is significantly smaller and, well, it offers no pollen.) If there were a simple gene coding for male sterility, one would expect it to be heavily selected against, so that gynodioecy would die out rather quickly. Instead, there are many Lamiaceae plus a few other plant groups showing this phenomenon, so the explanation must be more complex.