Cardinal creeper is widespread around the tropics but the plants show marked variations in the leaves and corolla.
It is thought that it is not a species plant but a variant or hybrid of Ipomoea lineolata which is a variable species itself.
Ipomoea horsfalliae is an evergreen twining liana (woody vine) with stems up to 10 m long.
Stems have lenticels (small nodules) but no hairs.
The alternately arranged dark green leaves are on petioles.
The blades are round in outline but deeply divided into 5 (3 to 7) leaflets that have no petiolule.
The leaflets are ovate, obovate, oblong, lanceolate or elliptic with a pointed tip.
The middle ones are usually larger than the others.
The edges can be smooth, slightly toothed, lobed or wavy and there are no hairs.
Axillary inflorescenes, up to around 15 cm long are on a stalk or peduncle.
They are often branched and the upper flowers on each branch open first.
Flowers are on a stalk or pedicel up to 1.5 cm long with a bracteole at the base.
The 5 free sepals are in 2 whorls often with the outer ones being slightly shorter.
Up to 1 cm long they are ovate to elliptic, green and blackish purple and without hairs.
The petals are fused into a funnel-shaped tube around 5 cm long with a spreading top (lip) around 3 to 4 cm across.
The lip has 5 lobes with a rounded tip.
The corolla is a bright red to purplish-red with mid petaline bands of the same colour.
The 5 stamens are inserted near the bottom of the corolla tube.
There is a dense clump of white hairs just above the base of the filaments and a few on the adjacent corolla.
The very pale purple filaments hold the anthers in or just above the throat of the tube.
Anthers open inwards through longitudinal slits.
The superior ovary has a single style with the bi-lobed stigma held just above the anthers.
There are 2 locules with 2 ovules in each.
The capsular fruit, with a beak from the style are rarely seen.
They have up to 4 seeds that have long hairs.