Family Apocynaceae.
There are 12–15 species but various sources give different information on them.
Some names are seen as both species and synonyms. For example –

  • A. cathartica is seen as a species and a synonym for A. schotti which is also seen as a species.
  • A. hendersonii is seen as a species and a synonym for, and a variety of, A. cathartica.
  • A. grandiflora and A. williamsii are seen as species and as varieties of A. cathartica.
  • A brasiliensis, A. magnifica and A. nerifolia are seen as species and as synonyms for A. schotti.

Also the same common names are applied to more than one species.
Two species are naturalised in Australia – A. cathartica and A. blanchetti.

Evergreen shrubs and some with stems that can clamber over any support like a vine.
A few are small trees and all have a white latex in the tissues.
The simple leaves, on short stalks, are opposite or in whorls of 3 to 5.
The blade can be smooth or have some hairs and there are axillary glands.

Inflorescences, terminal or between the leaf bases, are branched or unbranched.
There are bracts and bracteoles at the base of the inflorescence and flower stems respectively.
These have glandular hairs.
Flowers, with parts in 5’s, tend to be large and showy and often a bright yellow.
The sepals may be of different sizes.
The petal bases form a narrow corolla tube with a wider throat with scales or hairs.
The outward spreading, overlapping lobes may be twisted.

The short stamens are inserted near the top of the tube below the tufts of hairs.
Below the filament attachment, and projecting into the tube, is a densely hairy ridge.
The anthers form a cone around the style head to which they are stuck but not fused.
The disc, around the base of the ovary, is annular or slightly lobed.

There is 1 ovary of 2 fused carpels with 2 locules.
Each has numerous ovules attached to the walls in up to 5 rows.
The cylindrical style head has 2 short apical lobes, hairs and a lobed frill at the base.
A sticky secretion attaches it to the anthers.

The fruit, not commonly seen, are ovate to elliptic septicidal capsules with long spines.
Woody when mature, each of the 2 chambers contains flattened seeds with a marginal wing.

There are many varieties and cultivars in shrubs (some dwarfs), or vines with single or
    double flowers in yellow, peach, white, cream, orange, reddish, chocolate or white.

A. blanchetti is a vine with rough, hairy leaves and purple flowers around 10 cm long.
A. cathartica, a shrub or vine with smooth leaves, has bright yellow flowers around 10 cm long.
A. williamsii has double yellow flowers.
A. schotii is a small shrub with yellow flowers to around 6 cm long.