Gasteria retusa, like most other species of Gasteria, grows in dappled shade of small shrubs in its Karoo habitat. The plants benefit from the protective cover of thorny ‘nurse’ shrubs such as Carissa haematocarpa. The mottled leaves of Gasteria retusa allow it to blend in with its environment making it inconspicuous and difficult to detect. Also, the leaves of the plant are brittle and the leaf sap also not bitter. The natural enemies are herbivores such as rock rabbits (Procavia capensis) and porcupines (Hystrix africaeaustralis). When plants are grazed, any broken or damaged leaves in the leaf litter will callus and spontaneously root, soon forming plantlets. The plant thus uses the disturbance and damage as a means of vegetative regeneration. This is termed ‘passive resistance’. This vegetative reproduction method is also seen in many of the companion plants such as Adromischus, Crassula and others.

The succulent leaves of Gasteria retusa become turgid after rain in the winter months. This moisture-conserving strategy is essential for its survival during the long dry summer months. During periods of drought the leaves become reddish.

Growing below a nurse shrub such as Carissa haematocarpa also has its advantages. This nurse shrub not only provides shade during the long sunny days but the very thorny nature of the nurse shrub protects the succulent plants from grazers and trampling. Gasteria retusa has shallow roots and also benefits from the leaf litter layer.

The inflorescence appears in winter and the upper parts bearing the flowers are usually exposed above the canopy of the nurse shrub, thus clearly visible to, and pollinated by, local sunbirds. After successful pollination the capsule becomes erect and once ripe will open from the top, needing gusts of wind for effective dispersal of the seeds.

Fig. 6. A Southern Double-collared Sunbird (Cinnyris chalybeus) feeding on Gasteria retusa flowers in the Stone Plant House, Kirstenbosch NBG.