This is a member of the Acanathaceae family of plants, hailing from South India and Sri Lanka, and is sometimes known colloquially as pewter bush. I have previously referred to it as Strobilanthes gossypinus but this appears to be incorrect. It is a beautiful plant growing to a little over a metre in height, with exquisite velvety silver foliage: young leaves have a golden sheen. It forms a neat, rounded shape and it is also drought tolerant: I grow it near my letterbox at the top of a long driveway, an area which is rarely watered. It can grow in full sun or - usefully - dappled shade. Some growers believe it does best in part-shade. It needs good drainage and likes to be mulched. It doesn't like frosts. It is also said to be suitable for seaside gardens. It is an excellent background shrub for drought-tolerant plants such as rosemary, bearded irises, wallflowers and Osteospermum. I also have it growing near to Salvia leucantha 'Santa Barbara', which has a silvery cast to its leaves too; and it is a brilliant partner to many of the other compact Salvia specimens, providing a foil to blue, cerise, pink or white blooms.
It may never flower but it it does this is likely to be in winter, with stunning lilac flowers in racemes, making the branches arch over like a fountain. But ... I have read that flowering is sometimes a prelude to its imminent demise - which may be a myth, but maybe one should take cuttings just in case. I have found the cuttings slightly tricky - they should not be enclosed and the potting mixture should be free-draining. I believe it is also possible to grow it from seed.
Postscript: my original plant did eventually die after flowering. I still love this plant, and have obtained another one, but it is worth knowing what may happen.
Flowers in June, July, August.