Kahakuloa operculispora, a new Hawaiian simple thalloid liverwort in a new genus and family, Kahakuloaceae (Fossombroniales)

Kahakuloa operculispora, a new simple thalloid liverwort endemic to Hawaiʻi, so far only known from high elevation bogs in western Maui, is described and illustrated. The thallus has prominent reddish-purple rhizoids, uniseriate ventral slime papillae and lacks scales. The plants are dioicous; male plants have antheridia sunken in several rows of dorsal chambers, subtended by scales, while female plants have clustered archegonia enclosed by thick, barrel-shaped involucres that develop serially at the plant apex, before fertilization, and are arranged in a single dorsal row at maturity; perichaetial scales and pseudoperianths (defined as involucres developing after fertilization) are lacking. The capsules are spherical, 2−3 stratose, and dehisce irregularly; the spores are areolate and have a unique operculum-like disk on the proximal face. Molecular and morphological evidence supports placement of the plant in a new genus and family in the order Fossombroniales, suborder Fossombroniineae. Kahakuloa is the first liverwort genus endemic to Hawaiʻi, and Kahakuloaceae is the only known endemic Hawaiian land plant family.