GERANIACEAE Geranium Family | A small but very widely distributed natural order of dicotyledons belonging to the subclass Polypetalae, containing about 360 species in 11 genera. It is re-presented in Britain by two genera - Geranium (Crane's Bill) and Erodium (Stork's-bill), to which belong nearly two-thirds of the total number of species. The opposite or alternate leaves have a pair of small stipules at the base of the stalk and a palminerved blade. The flowers, which are generally arranged in a cymose inflorescence, are hermaphrodite, hypogynous, and, except in Pelargonium, regular. The parts are arranged in fives. There are five free sepals, overlapping in the bud, and, alternating with these, five free petals. In Pelargonium the flower is zygomorphic, with a spurred posterior sepal and the petals differing in size or shape. In Geranium the stamens are obdiplostemonous, i.e. an outer whorl of five opposite the petals and alternates with an inner whorl of five opposite the sepals; at the base of each of the antisepalous stamens is a honey-gland. In Erodium the members of the outer whorl are reduced to scale-like structures (staminodes), and in Pelargonium from two to seven only are fertile. There are five, or sometimes fewer, carpels, which unite to form an ovary with as many chambers, in each of which are one or two, rarely more, pendulous anatropous ovules, attached to the central column in such a way that the micropyle points outwards and the raphe is turned towards the placenta. |
