Phillip Island hibiscus is critically endangered due to the small number of plants and the lack of genetic diversity.
They are shrubs up to 2.5 m high and wide with dense foliage.
The smaller pale green twigs are covered in simple and stellate hairs.
The alternate leaves are on a petiole up to 1.5 cm long covered in very short hairs.
The ovate leaves are up to 6 cm long and 4 cm wide.
The edge has blunt teeth and shallow lobes except for the almost flat base.
The lower surface has prickly hairs on the veins and the upper a few stellate hairs.
Inflorescences are solitary axillary flowers around 7 cm across when fully open.
They are on a short very hairy stalk or pedicel nearly 1 cm long.
The epicalyx has 5 (3 or 4) separate involucral bracts immediately under the calyx.
They are green, circular to oblong and have a mucro (an abrupt point) at the tip.
Up to 6 mm long they are covered in short matted white hairs.
The bell-shaped calyx has 5 sepals with the bases fused for 1/2 to 2/3 of their length.
The pointed triangular lobes curve outwards slightly.
There are tiny matted hairs on the outer surface and on the inner surface of the lobes.
The epicalyx and calyx remain on the fruit.
The 5 free overlapping oblong petals, nearly 6 cm long spread out and curl back.
They have hairs on the outer surface.
Initially the petals are pale green, white or cream with a dark magenta or purplish base.
As they age they become pale mauve to red which accentuates the parallel white veins.
The twisted reddish-purple and white staminal column of fused filaments extends past the corolla.
The lower part is bare with the short free ends of the filaments holding the anthers near the top.
The young orange kidney-shaped anthers mature to a deep purple and release yellow pollen.
The 5 style branches emerging from the staminal column are a deep purple.
The small similarly coloured spherical stigma lobes have short hairs.
The smooth green conical ovary has 5 locules.
The fruit are conical capsules up to 1.5 cm long with numerous wrinkled seeds.
Nectaries are present.