Taxonomic Revision of Corsia (Corsiaceae) Reveals Over‐Estimated Mycoheterotroph Diversity in Papuasia: 25 Species Become 10.

Corsia (Corsiaceae) is a remarkable genus of achlorophyllous, fully mycoheterotrophic plants distributed across New Guinea, the Solomon Islands, and Northern Australia. The genus has often been considered an example of adaptive radiation amongst mycoheterotrophic plants, with 25 narrowly endemic species, most known from just one or two specimens. The previous revision by van Royen in 1972 recognized 25 species from just 45 specimens. Here, we present a comprehensive taxonomic revision of Corsia based on the c. 150 specimens now available, including critical re-examination of type material. Many previously recognized species lack consistent diagnostic characters and are here synonymized, reducing the number of accepted species from 25 to 10, with the description of one species new to science: Corsia mantarayoides. Rather than representing a radiation of micro-endemic taxa, Corsia species are shown to be more morphologically variable and geographically widespread than previously considered. These findings suggest that perceived rarity can reflect sampling artifacts and taxonomic inflation rather than true biological patterns. This has direct implications for conservation prioritization, where inflated species counts can misdirect efforts and resources. More broadly, our study highlights the critical importance of rigorous, up-to-date taxonomy in accurately documenting biodiversity, particularly in cryptic and rarely encountered plant lineages.