Baker M. A., A Multivariate Study of Morphological Characters for Echinocactus horizonthalonius and E. texensis (Cactaceae) and Description of a New Subspecies, E. horizonthalonius subsp. australis, Diversity, 2022, 14(12):1020, doi: 10.3390/d14121020
A multivariate comparison of stem traits in Echinocactus horizonthalonius populations, with Homalocephala texensis (Echinocactus texensis in the paper) as a comparison group. It includes a description of subspecies australis, a key, habitat information, maps and a discussion of regional morphological variation.