Abstract The new species Kadua haupuensis is described and illustrated from the isolated Mt. Ha’upu region of Kaua’i, Hawaiian Islands. This new species belongs to Kadua subg. Kadua sect. Wiegmannia. It is characterized by a subdioecious (leaky dioecious) breeding system and appears most closely related to another apparently dioecious species endemic to Kaua’i, Kadua flynnii, with which it is compared. Although the only original wild population is critically endangered and may possibly be extinct, this new species has been successfully propagated and is currently secure in cultivation.
