|Urticaceae - Nettle Family
Above: the common Stinging Nettle (Urtica dioica). The small greenish flowers are borne on catkins. The sexes
are separate in this species. In the female plant (above left) the catkins hang down more, whereas in the male
(top right) they tend to stick out horizontally. There are no petals, instead four green sepals surround either a
single carpel in the female (superior ovary) or four stamens in the male. Male: K4 C0 A4 G0, female: K4 C0 A0
G1. Parietaria has similar flowers, but with male, female and hermaphrodite flowers borne on the same plant.
The nettle family is extremely diverse family of flowering plants. Most are herbaceous, like the familiar Stinging
Nettle (Urtica dioica) and the Wall Pellitory (Parietaria diffusa) but a few are trees.
Left and right: The Stinging Nettle is so-called
because lightly touching the leaves or stems will
result in quite painful stings. The stem and leaves
are covered in stinging hairs. These hairs are made
of silica (essentially biological glass, an example of
the use of silicon in plants) and are brittle and
sharp. They easily penetrate the skin and break off
their tips to release the formic acid (methanoic acid)
contained inside them. This is the same acid used in
many ant and in wasp stings.
Left: female flowers - consist of
four green sepals (the calyx)
surrounding a single carpel. The
carpels are beginning to ripen
into fruit in this plant. The fruit is
an achene containing one seed.
(An achene is a fruit consisting
of a single carpel with dry outer
layers and which does not open
when ripe). Right: male flowers
just beginning to open. These
consist of four green sepals
enclosing 4 stamens.
Article last updated 11/10/14 ...