Taxonomic turmoil in Pterostylis

Ryan O’Donnell, Hansjörg Eichler Fund Awardee, investigates NSW Greenhood orchids

An integrative taxonomic study

The ‘Greenhood orchids’—a predominantly Australian group of terrestrial orchids comprising over 300 species in the genus Pterostylis—are a key example of a group in ‘taxonomic turmoil’. While recent plastid phylogenomic work elucidated subgeneric limits within the group (Nargar et al. 2022), interspecific relationships could not be satisfactorily resolved.

The majority of species in Pterostylis have not been tested rigorously using molecular evidence but recent studies of pollination and chemical ecology revealed the presence of sexually deceptive pollination. The production of distinct floral volatiles associated with insect sex pheromone mimicry has been demonstrated to underpin reproductive isolation in other sexually deceptive Australian orchids, so it is hypothesised that similar differences in floral chemistry may reveal the presence of discrete boundaries between morphologically and genetically invariable taxa in Pterostylis.

Upon starting my PhD, my supervisors and I began the search for a suitable species complex in Pterostylis that might benefit from a rigorous integrative study. After some consultation with Lachlan Copeland and Gary Backhouse, we arrived at the Pterostylis macrosepala complex as a potential study group. Currently five separate species spanning from the South West Slopes to the Northern Tablelands of New South Wales have been recognised —P. crassa, P. macrosepala, P. readii, P. tenuis, and P. umbrina

Funding from a Hansjörg Eichler Research Frund grant has supported in part molecular sequencing to investigate taxon boundaries in this intriguing group. More on this project can be found in the current ASBS Newsletter.

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