Urticaceae – Nettle family.
The nettle family has 45 – 54 genera and 550 to 2625 species depending on what genera are included.
Compared to some other families it is not well researched, there is little genetic information
and many species are yet to be properly described.
Many of the morphological features used to differentiate members are only 1 mm or so in size.
It is divided into Tribes – Boehmerieae with Pipturus, Elatostemateae with Pilea and Urticeae with nettles.
Other are Forsskaoleeae and Cecropieae (not always included in the family).
The plants are characterised by having leaves with stipules and cystoliths, inflorescences
with bracts and a perianth of 1 whorl of tepals.
There are very few trees in the family with most being shrubs, herbs and some vines.
Some have a watery coloured sap.
There are usually hairs on the stems and leaves and some are stinging e.g. nettles.
Leaves are alternate (usually in a spiral), or opposite.
They are simple, usually entire and rarely lobed or dissected (palmatifid).
Venation can be triveined or pinnate, rarely palmate.
The leaf edges can be smooth or with small sharp to blunt teeth.
Cystoliths are collections of calcium carbonate crystals seen in dry specimens.
Leaves usually have stalks and 1 or 2, free or fused stipules.
Inflorescences are almost always axillary, rarely terminal.
The small flowers are almost always in loose or tight clusters.
The inflorescence is often a spike or it can be variously branched.
They can also form globular clusters or heads on a common receptacle.
There may or may not be a whorl of bracts (involucral) at the base of the flower.
Bracts can be small or surround the flowers.
The flowers can be bisexual or unisexual.
Plants can have either male or female flowers or both.
There can also be bisexual and unisexual flowers on one plant.
Male flowers are on stalks.
Their perianths have 4 to 5 (2 – 9) white or green, sepal-like tepals.
Tepals are free or joined and in 1 whorl.
There are 4 or 5 (2 – 6) free, fertile stamens in 1 whorl.
They are opposite the tepals.
The filaments are usually curled and the anthers open via longitudinal slits.
The sudden straightening of the stamen disperses the wind-blown pollen.
There is usually a rudimentary carpel (a pistillode).
Females flowers, usually with no stalk, have 2 to 4 tepals or none.
They are a greenish or reddish colour.
They may enlarge as the fruit grows after fertilisation.
There is 1 carpel (or more that are fused to give 1 locule).
There is 1 short style (0 – 2) and 1 (2) stigma/s.
The ovary is usually superior but sometimes inferior and has 1 ovule.
There are sometimes infertile scale-like stamens (staminodes).
Placentation is basal.
Bisexual flowers have 4 tepals and stamens, and 1 carpel.
Fruit, with 1 seed can be dry or have a fleshy layer derived from the swollen perianth.
J.F.
