Pelargonium uliginosum (Geraniaceae: section Hoarea), a new species from Western Cape, South Africa, and an updated key to the species of the P. dipetalum group

•Pelargonium uligonosum is a new species allied to P. dipetalum.•It is diagnosed by glabrous, bi- or tripinntisect leavers.•A key is presented to all eight species of the Pelargonium dipetalum group.

The new species Pelargonium uliginosum is a local endemic of Breede River Alluvial Fynbos in the upper Breede River Valley, Western Cape, South Africa. One of the eight species of sect. Hoarea with only the posterior two petals developed, it is distinguished by its glabrous, bi- or tripinnatisect leaves with subulate ultimate segments each tipped with one or sometimes two setae. The new species is described and illustrated, and we include an updated key to the species of the Pelargonium dipetalum group.