Thank you, Alisdair. Yes, it resembles the 'Royal Bumble', but the colour of the flowers is not right: this one has cerise-magenta-coloured flowers on very dark stems, with a touch of white at the 'throat'. It looks very much like Salvia microphylla 'Cerro Potosi' (common name: cherry sage); S. microphylla is a part of a botanical complex with S. greggii, S. muelleri and S. coahuilensis, I read. Anyhow, none of these need much water and they seem to be quite tough, so I hope they will get established here.