There is a detailed article on Hibiscus heterophyllus and photos of flowers and of the plant.

While much of this article can be applied to H. divaricatus there are some differences between the two species.

1. NATURAL RANGE

Hibiscus divaricatus is less widespread than Hibiscus heterophyllus.

Link pending.

2. FORM OF PLANT

The bushes grow differently when grown from seed, that is, in their natural environment. Hibiscus heterophyllus is a tall, erect shrub up to 6m. high with branches that are ascending.
The lower branches are longer than the upper ones and so the plant has a pyramidal form.

Reference: Keith Williams, Native Plants of Queensland, Vol. 1, Cranbrook Press, 1979.

Hibiscus divaricatus is normally only 5m or less and usually has an erect central stem that branches fairly close to the ground. The branches are fairly long, straight, generally ascending. The lower ones grow at an obtuse angle to the main stem before becoming ascending and produce short stems which are mainly the flowering stems.

Reference: Keith Williams, Native Plants of Queensland, Vol. 1, Cranbrook Press, 1979.

However, these differences in growth habit virtually disappear when plants are grown from cuttings and tip-pruned regularly after planting out.

3. FLOWERS AND LEAVES

The flowers of Hibiscus divaricatus are crimson centred and are up to about 10 cm across. The leaves are dark green, up to 10 cm and may be long or deeply 3 lobed.

The flowers of Hibiscus heterophyllus have a large crimson central blotch and are up to about 15 cm across. The leaves are either narrow, broader or deeply lobed, up to 15 cm long.

SUMMARY
There are differences in these two species, such as differences in distribution, form of the plant and the size and colour of the flowers and the shape and colouring of the leaves but both perform well in horticulture with the bright gold form of H. divaricatus providing a vivid accent plant in the garden. Growing both species results in a longer flowering period than growing either alone.