There are around 260 species from Central and South America.
Cuphea carthagenensis is naturalised in Queensland and New South Wales.
They are herbs or sub shrubs up to 2 m high.
Most have glandular hairs, sometimes forked, on the stems, leaves and flowers.
Leaves are mostly opposite and occasionally in whorls of 3 to 5.
They are on petioles and the blades are typically narrowly elliptic.
Inflorescences, axillary or interpetiolar, can be small clusters or a solitary flower.
Plants produce masses of tubular flowers often for most of the year.
The bilaterally symmetric flowers are on hairy stalks.
There may be 2 bracts, either leaf-like or very narrow, or there may be none.
The tubular to urn-shaped hypanthium (floral tube) varies from 3 to 40 mm long.
The base can be swollen, spurred or narrowed.
The hypanthium is hairy and can be mixes of green, red and yellow.
On the rim are 6 hairy, pointed sepal lobes sometimes with the dorsal one enlarged.
Between the lobes there may be appendages that can be shorter to much longer than the lobes.
There may be a glandular nectary in a spur or an annular one around the ovary.
There are usually 6 (0, 2, 4 or rudimentary) petals.
They insert into the top of the inner surface of the hypanthium between the sepal lobes.
They have a narrow, clawed base and slightly wrinkled blades.
The dorsal pair (nearest the axis or stem) may be larger or smaller than the others.
There are 11 (4, 6, or 9) stamens inserted at different levels into the hypanthium.
The anthers can be inside or above the end of the hypanthium.
The ovary, of 2 carpels, is partially 2-chambered.
The thin style can hold the stigma in or above the tube.
There are 2 to over 100 ovules with axile attachment to the placenta.
In a few species the ovary develops into a capsule in the usual way.
However, is most species of Cuphea the ovary development and seed release is very different.
Just after fertilisation the dorsal sides of the hypanthium and ovary split.
The placentae, with the very immature ovules, rotates laterally over 90º through the splits.
This leaves the ovules exposed as they develop into seeds.
The thin, almost transparent ovary walls and style remain in place in the hypanthium.
The flattened seeds, often around 2 mm, may have a very narrow wing.