Segments and reproductive organs
In the 2019 comparative analysis, the plant was described as a low shrub with a fibrous root system, globose segments and awl-shaped spines. Leaves are seasonal and shed. Segment connections are intermediate in strength between species with very fragile or firmly joined stems. [Las Peñas et al. 2019, appendix 1]
Flowers have a pale perianth in white and pink shades. Areoles on the outer stem-derived part of the flower may produce spines. A dry, dehiscent fruit develops at maturity. The seed is surrounded by corky tissue derived from the ovule's funiculus. These traits link the plant to the group also containing T. articulatus and T. aoracanthus. [Las Peñas et al. 2019]
Distinctness from Tephrocactus geometricus
The study's authors retained T. alexanderi and T. geometricus as separate species. Morphological traits and DNA differentiation supported separation. In this comparison, T. geometricus had stronger segment connections and a different combination of armament on the stems and stem-derived part of the flower. Current POWO also accepts the two species separately. [Las Peñas et al. 2019] [2-WWW]
The cytogenetic material of T. alexanderi was diploid, with 2n = 22. Endopolyploidy was also found, meaning the presence within tissues of nuclei with multiplied DNA content. The plant's chromosome number and DNA content in individual cells describe two levels of organisation in this case. [Las Peñas et al. 2019, Table 2]
Research material and identification
The studies included material from Argentina, with identifications linked to voucher specimens and collection sites. Origin and the structure of mature segments and flowers are particularly useful when comparing plants from old collections. The atlas retains the name T. geometricus in a separate species profile. [Las Peñas et al. 2019] [2-WWW]
Cultivation in archival material
The archival review of Tephrocactus cultivation describes dry dormancy at temperatures no higher than 10°C and propagation by rooting detached segments. The author notes that severe drying may increase segment shedding. The recommendations concern the group discussed, with no defined minimum temperature or separately determined rooting percentage for this species. The retained earlier archival profile includes references to pages in the material. [Kaktusy i Inne 2005c, p. pliku 2–4]
Synonyms and names in the literature
Opuntia alexanderi · Opuntia alexanderi var. bruchii · Opuntia alexanderi var. subsphaerica · Opuntia bruchii · Opuntia bruchii f. brachyacanthus · Opuntia bruchii f. macracantha · Opuntia flexuosa · Tephrocactus alexanderi subvar. brachyacanthus · Tephrocactus alexanderi subvar. macranthus · Tephrocactus alexanderi var. bruchii · Tephrocactus alexanderi var. subsphaericus · Tephrocactus bruchii · Tephrocactus bruchii f. brachyacantha · Tephrocactus bruchii subvar. macracantha · Tephrocactus flexuosus · Tephrocactus microsphaericus · Tephrocactus riojanus · Tephrocactus subsphaericus [2-WWW]