Background and Aims:

Parasitic plants represent approximately 1% of the world’s angiosperm diversity. The highest richness of parasitic plant species among angiosperms belongs to Orobanchaceae, the only family with three main nutritional stages: autotrophic, hemiparasitic, and holoparasitic. Hemiparasitic genera are the most diverse, unstudied, and sometimes neglected within Orobanchaceae. Pedicularideae, the largest tribe of hemiparasitic taxa in Orobanchaceae, contains several poorly known genera. One of these is Lamourouxia, a genus of 30 species distributed throughout the Americas, but mostly endemic to Mexico. Due to the lack of knowledge about the biogeographic patterns, endemism, and conservation status of Lamourouxia species, the objectives of this study were to estimate their species richness and endemism, determine the areas of endemism in the Americas, and assess their conservation status.

Methods:

Applying a taxonomic revision of physical and digitized herbaria specimens, citizen science observations, and scientific open access databases, we conducted biogeographic analyses for the whole genus. Moreover, the conservation status of all Lamourouxia species was assessed following the IUCN Red List guidelines.

Key results:

The highest species richness, highest weighted endemism, and corrected weighted endemism values occurred in southern Mexico. Three areas of endemicity were distributed throughout western Mexico. Four species were classified as Endangered (EN), and three as Critically Endangered (CR) according to the IUCN risk categories. Endemic and rarely recorded Lamourouxia species were mostly distributed in unprotected areas in the Sierra Madre del Sur, Mexico.

Conclusions:

The Mexican Transition Zone is the center of diversification of Lamourouxia, and one third of the genus is endemic to this region. It is strongly encouraged to carry out actions to conserve threatened species of Lamourouxia, which are distributed in the Sierra Madre del Sur, the biogeographic province with the highest number of endemic species in Mexico.