I was looking at this photo of one of the Geraniaceae family and trying to think what it is that defines it as a Geranium. I guess we instinctively know what plants ‘look a bit like’, without having to think about it too much. Perhaps there is a lot of pink going on and the leaves seem to be a bit on the circular side like the garden Geranium(Pelargonium). However these characteristics are not accurate enough, as the Geraniaceae can have different coloured petals and different shapes of leaf, so I am left with a fairly indistinct set of features. These include 5 petals, 5 sepals, 5 stigmas, 5 or 10 stamens and leaves that are either pinnate or palmate.
The most interesting bit however is the sticky-out long beak which are elongated parts of the ovary that give the 2 British genera their common names, Crane’s Bill(Geranium) and Stork’s Bill (Erodium). The main problem is that these are not always apparent if the plant is early in its flowering phase.
However if we take a look inside and strip away the sepals; then there is this
The long-beak has not yet started to form, but the 5 lobed stigma is clearly visible at the end of the long style. If we manage to find a mature one with the long-beak sticking out then we see this,
When the seeds are ripe the beaks roll up from the tip (where the stigma was) to eject them.
Apparently flowers of the Geranium genus have rolled beaks whereas Erodium have twisted beaks.