Classification of Boraginaceae subfam. Ehretioideae: Resurrection of the genus Hilsenbergia Tausch ex Meisn.

The genus Hilsenbergia (Boraginaceae: Ehretioideae) is resurrected to accommodate a group of east African and west Indian Ocean species that have been included in Ehretia or Bourreria by other authors. These species differ from the pantropical Ehretia in having 4 winged to ridged pyrenes in the fruit, flowers with valvate calyx lobes, and fleshy, urceolate corollas. Hilsenbergia differs from the Neotropical Bourreria in having fruits that lack a fibrous connection between the apex of the pyrenes and the gynobase and having smaller flowers with urceolate corollas, as well as in its African/Indian Ocean distribution. As defined here, Hilsenbergia consists of 18 species, 13 of which are endemic to Madagascar and all of these are newly described. A key and nomenclatural notes for all species and full descriptions for the thirteen new species that are described are provided. Conservation analyses indicate that all of the Hilsenbergia species from Madagascar are threatened and five species are critically endangered and nine are endangered.