The tropics are the repository of much of the world's biodiversity, yet are undersampled relative to temperate regions. To help fill this knowledge gap, a paper in BMC Biology explores diversity patterns in tropical African plants, as revealed by the RAINBIO database. The paper documents spatial variation in diversity and data coverage, but also highlights the challenges faced in quantifying diversity patterns using data collated from a range of sources including herbaria.See research article: http://bmcbiol.biomedcentral.com/articles/10.1186/s12915-017-0356-8 .