The Purple Allamanda, commonly cultivated, is naturalised in a few areas in Queensland.
They are vigorous scrambling shrubs up to 3 m high.
The young branches are hairy.
The simple leaves are opposite or in whorls of 4 (3 – 5).
With a stalk only 1 to 2 mm long the blade can appear to be directly attached.
The blades, around 9 to 12 cm long and 3 cm wide, are elliptic to obovate.
The tip may be a long or short point.
The surface feels rough due to the short, stiff hairs.
These are on both surfaces, mainly on the veins and denser underneath.
Inflorescences are on stalks up to 2.5 cm long.
Flowers, on stalks around 6 mm long, are up to 10 cm long and wide.
The 5 hairy sepals are around 1.5 cm long and 6 mm wide.
The corolla is funnel-shaped with overlapping, flaring lobes.
It is purple to pinkish with a darker throat.
There are tufts of hairs on the bases of the lobes that partly hide the anthers.
The 5 stamens, on short filaments, insert on the top of the narrow part of the corolla tube.
There are hairs beside, and below, the filaments.
The anthers open inwards via long slits.
They converge around the style head but are free of it.
The 2 carpels are fused and the ovary has 2 locules with numerous ovules.
The long style has a large style head.
Cultivars extend the colour range to shades of light to dark purple, mauve, magenta,
reddish-purple, dark red, cream and brownish to bronze.