The genus Mediocalcar is revised. Fifteen species and five subspecies are recognized, of which the following are new: Mediocalcar congestion Schuit., M. umboiense Schuit., M. versteegii J.J. Smith subsp. amphigeneum Schuit., M. versteegii J.J. Smith subsp. intermedium Schuit. and M. versteegii J.J. Smith subsp. vulcanicum Schuit. All species are illustrated by line drawings, several also with colour plates. Aspects of the ecology, biogeography, morphology and systematics of Mediocalcar are discussed.