This pretty Plectranthus has been growing in my garden for a number of years under various aliases, including 'Purple Dazzler', and it has only been recently that I have felt more certain of its real species name, which in fact means 'doubtful or uncertain', because of confusion about its nomenclature! It is a low-growing, groundcover plant (ht to 50 cm), with relatively large heads of striking purple spires of flowers on dark stems in autumn. It comes from South Africa, as many of the genus do, and it is well suited to Sydney's climate.
It forms an effective carpet in shaded parts of the garden under trees or shrubs, or growing with other Plectranthus, such as the shrubby Plectranthus ecklonii, 'Cape Angel' cultivars or the white-spired Plectranthus ciliatus. I also like it paired with Odontonema tubaeforme, which has brilliant red spires of flowers shaped very like those of Plectranthus ambiguous at the same time of year. Many of the cane and shrub Begonia are in flower when Plectranthus ambiguus blooms and it is a good companion for them, providing a colour contrast to their pink, white, red or orange inflorescences. I also like to grow it with purple-leaved Tradescantia pallida 'Purpurea' nearby. It could also be grown in a hanging basket. It should be pruned back after flowering (or in late winter in cooler suburbs) and it strikes very readily from cuttings taken in autumn or spring. In my garden it self-seeds a little, but I have always been able to find homes for these offspring amongst other gardeners who have admired it.