There are about 16 species none of which are native to Australia.
Leaves, on petioles, are opposite and 1 to 3-pinnate.
Inflorescences are terminal or axillary.
The bell-shaped calyx has up to 5 lobes or a flat top.
The bell or funnel-shaped, bilabiate corolla has a short or long tube.
There are 2 unequal pairs of stamens and usually a staminode.
There is an annular disc around the ovary.
The ovary has 2 rows of ovules in each locule.
There is a single style and a 2-lobed stigma.
The loculicidal capsules hold flat seeds with transparent wings.