Experimental Cross-Pollination to Test Species Boundaries: Are Parodia stuemeri and Parodia pseudostuemeri One Species?

Parodia pseudostuemeri Backeb. is not recognized as a separate species by authors such as Kiesling and Ferrari (1990) and Hunt (2006). It is considered synonymous with Parodia stuemeri (Werderm.) Backeb. Plants in the crosses conducted in this study are Parodia pseudostuemeri obtained from the type locality by the discoverer Mrs. Muhr; and Parodia stuemeri L 529 obtained from the Quebrada del Toro, Salta by Alfred Lau, both from Argentina. Crosses were made between Parodia stuemeri L 529 and Parodia pseudostuemeri (Muhr) and the corresponding reciprocal cross between Parodia pseudostuemeri (Muhr) and Parodia stuemeri L 529. The progenies of both crosses differed considerably. The first cross of Parodia stuemeri pollinated with Parodia pseudostuemeri succeeded. Very young seedlings matured into older seedlings, then into healthy vigorous young plants. The corresponding reciprocal cross failed. Seeds formed but very young seedlings and older seedlings died. Within two and a half years after sowing all died, probably due to genetic defects. There were considerable reciprocal differences. Results of the crosses are illustrated by comparative photographs of the two progenies in the successive stages of development. These differences can be explained by an incompatibility between the two parental genetic materials in the corresponding reciprocal cross of Parodia pseudostuemeri pollinated with Parodia stuemeri. Therefore, we conclude there is no close relationship between the two crossing partners and suggest Parodia pseudostuemeri be viewed as a separate species from Parodia stuemeri.