Segments, spines and flowers
Globose segments form a small, branched plant with fibrous roots. In the material compared in 2019, segment connections were classified as strong. The specimens studied had very limited stem armament, and the outer stem-derived part of the flower was spineless. [Las Peñas et al. 2019, appendix 1]
Flowers have a perianth ranging from white to pink. Sepals lack the sharp, spine-like tips described in some relatives. A dry fruit develops after flowering and opens at maturity. The seed covering is corky. Fruit and seed traits connect the species with the typical Tephrocactus lineage. [Las Peñas et al. 2019]
Boundary with Tephrocactus alexanderi
The species has sometimes been included in a broadly defined T. alexanderi. In 2019, Las Peñas and coauthors retained both species based on a set of structural traits and DNA analysis results. Current POWO classification also maintains separate records. [Las Peñas et al. 2019] [2-WWW]
The chromosome number in the material studied was 2n = 22. Diploidy distinguishes these specimens from highly polyploid plants of T. aoracanthus and some T. articulatus, but the number 22 also occurs in other species of the genus. Identification requires a set of traits, including the strength of segment connections and flower armament. [Las Peñas et al. 2019]
Synonyms and names in the literature
Opuntia geometrica · Tephrocactus alexanderi subsp. geometricus [2-WWW]