Las Peñas M. L., Bernardello G., Divergence time estimation and mapping of morphological and cytogenetical data in the southern South American geophyte genus Pterocactus (Cactaceae), Taxon, 2021, 70(3):552-569, doi: 10.1002/tax.12497
A phylogeny of ten Pterocactus species recognised at the time, based on three chloroplast markers. The paper brings together stem and spine structure, flower position, chromosome numbers and DNA content. It also includes a model-based estimate of the timing of diversification in the genus.