Plectranthus saccatus is a soft, semi-succulent shrub with a woody base. The branches are tinged with purple and have soft hairs. The leaves are bright green, have large teeth along the margin and are dotted with transparent gland dots beneath. The shrub reaches a height of about 1.2 m. The flowers may have some purple markings and are borne on one side of the stem. Flowering occurs in summer to autumn (from November to May).

The large petals distinguish the stoep jacaranda from others in the genus. The flowers bear a vague resemblance to the Jacaranda mimosifolia flower, hence the common name (though it is no relation to the jacaranda). The colour of the flowers is also similar to those of the jacaranda and ranges from blue to lilac and sometimes white. Since it is a shade-loving plant, it is often used as a stoep (porch) plant. There are a number of different varieties and cultivars of this plant.

Plectranthus saccatus belongs to the sage or mint family (Lamiaceae) which has a very large representation in the Mediterranean regions. The family is characterised by aromatic leaves arranged in opposite pairs (decussate) and the two-lipped corolla.