Abstract erotica, Japanese giants face off and spring arrives in Oxford – the week in art

Fabulous flora … detail from Orchids by Sir Lawrence Alma Tadema showing at In Bloom: How Plants Changed Our World. Photograph: Private collection, USA, courtesy of the Richard Green Gallery, London

Exhibition of the week

In Bloom: How Plants Changed Our World
Lovely flower paintings to herald the spring, but all is not what it seems in this survey of how science, trade and tulip crazes helped shape the modern world.
• Ashmolean Museum, Oxford, from 19 March to 16 August