Alternanthera.
Plants of the World Online accepts 106 species many of which are now weeds.
Australia has 8 or 9 species with some becoming naturalised.
They are annual or perennial herbs or small shrubs and some grow in water.
The much-branched stems can be prostate, prostrate then erect, erect or scramble over other vegetation.
Stems, especially on young plants may have dense hairs that are usually lost over time.
The opposite leaves may have a petiole or be directly attached to the stem.
The ovate to lance-shaped blade may have dense to no hairs and a smooth or toothed edge.
Axillary and terminal inflorescences are 1 (or a few) heads or short spikes.
The spherical to ovoid heads or the spikes may be on a peduncle.
Each flower has 1 bract and 2 bracteoles at the base.
The bracts persist but the bracteoles may fall.
Flowers have no petals but 5 free tepals (sepals).
They may all be similar or the outer 3 may be longer than the inner two.
The white to purple tepals have edges that may be smooth or finely toothed.
The bases of the flattened stamen filaments are fused into a short tube.
There are typically 5 fertile stamens on the rim alternating with shorter or longer pseudo-staminodes.
Pseudo-staminodes are flattened filaments, with no anthers that have a smooth, toothed or frayed edge.
The number of stamens and pseudo-staminodes varies from flower to flower.
Anthers have 2 locules that open inwards through only one slit.
The spherical to obovoid superior ovary has 1 locule with 1 ovule.
The pendulous ovule is on a long stalk.
There is a short or no style with a spherical or rarely slightly bi-lobed stigma.
Fruit are a flattened, often membranous indehiscent utricle with the perianth attached.
Each has 1 reddish-brown seed.
J.F.
