A phylogenetic analysis of large-subunit (26S) ribosome DNA sequences suggests that the Corsiaceae are polyphyletic

Corsiaceae is a small family of mycoheterotrophic herbs composed of the genera Arachnitis, Corsia, and Corsiopsis. Due to a lack of DNA sequence data, previous molecular-based phylogenetic studies have not addressed adequately the position or circumscription of the family. Because mycoheterotrophy results in extreme vegetative reduction that may contribute to homoplasy in the form of character convergence, morphological-based studies that have addressed these issues may be misleading. Traditionally, Corsiaceae have been grouped with Burmanniaceae and Thismiaceae. However, other than mycoheterotrophy, there are few characters that support this relationship. Additionally, the monophyly of Arachnitis, Corsia, and Corsiopsis has been questioned. The present phylogenetic study, inferred from large-subunit (26S) ribosome DNA sequences, suggests that Corsiaceae are polyphyletic. Specifically, Corsia clusters with the order Liliales and Arachnitis appears as sister to Thismia (Thismiaceae) in a larger clade that also includes Burmanniaceae.