Plants of the World Online (Kew) recognises 566 species that are found worldwide with many from South America and South Africa.
There are up to 32 species in Australia with only 6 or 8 being native.
Seen as weeds and sometimes as ornamentals many are naturalised.
Commonly known just as ‘Oxalis’ other common names include sorrels and shamrocks as many have clover-like leaves.
With such a large genus there are many different combinations of features.
The annual or perennial plants are mainly herbs with a few succulents and shrubs.
Many have underground tubers, rhizomes or bulbs and some have a small or stout taproot with fibrous roots.
(A bulb is a small underground stem surrounded by large fleshy petiole or peduncle bases.
A rhizome is a narrow or swollen horizontal underground stem.
A stolon is a thin horizontal mainly above ground stem.
A tuber is a swelling on an underground stem or sometimes the roots.)
There may be no above ground stem with all the leaves being basal.
Ayny erect or prostrate above ground stems may be very short or tall and with or without branches.
Stems can be smooth or have a few to dense hairs that spread outwards or point up or down the stem.
Leaves can be basal from the rhizomes or on an above ground stem.
Alternate or pseudo-whorled leaves are on petioles from 1 mm up to 5 cm long.
Petioles can be cylindrical, flat, winged and smooth or with sparse to dense hairs.
Stipules may be absent and when present may be indistinct or obvious and sometimes not on all petioles of a plant.
From 2 to 15 mm long they may be just a small swelling on the petiole or a wider wing that tapers down onto the petiole.
Most have some hairs and there are frequently tiny cilia on the edges.
Some species have simple or pinnate leaves but most are 3-lobed and a few have numerous lobes.
Leaflets may have no petiolule (stalk) or a very short one.
Leaflets are commonly obcordate (inverted heart-shape) but some are linear, 3-angled, oblong or obovate.
The obcordate and obovate leaflets can have a shallow or deep notch at the tip that is narrow or wide.
Leaflets can have no hairs, a few or they may be dense and there may be orange or black spots of oxalate crystals (calli.)
Some have a pulvinus (a swollen area) on the petiolules that allows the leaflets to fold up in poor light.
Axillary inflorescences are on a short peduncle (stalk) or one up to 40 cm long.
There may be a single flower or an umbel with 2 or 25 flowers, on a pedicel all attached to the top of the peduncle.
Peduncles and pedicels have few to dense hairs that may spread out in all directions or all point towards the top of the stem.
There may be bracts on the base of the peduncle and bracteoles on the pedicels any of which may have calli.
Flowers have 5 ovate, oblong or lance-shaped overlapping sepals that are free or slightly joined at the base.
They may have hairs and 2 orange calli at the tip.
The 5 petals, free or slightly fused at the base may have a narrow claw base.
Petal colours include yellow, red, pink, salmon, violet, mauve, purple and sometimes white.
The 10 stamens are in 2 whorls of the same or different lengths and the filaments may be joined at the base.
There are 5 fused carpels and nectaries may be present.
When seen the fruit are a loculicidal capsule with a few seeds in each chamber.
Eight mms to a few cms long and smooth or ridged capsules can be narrow or have a swollen middle section.
Some species reproduce by small bulbils growing from a rhizome, stolon, an old bulb or in the leaf axils. These may be prolific.