Budowa geofitu
Much of the plant lies underground as a thickened root. Short, globose segments develop above the surface to form a low clump. The characteristic spines have a comb-like arrangement. The 2019 account highlighted the absence of glochids and of developed areoles on the receptacle, the stem-derived part of the flower. [Las Peñas et al. 2019]
Flowers have a pale, white or pinkish perianth. Fruit is dry and opens at maturity. A hook-shaped embryo develops in the seed, and the outer covering contains abundant light tissue with air spaces. [Las Peñas et al. 2019] [Stuppy 2001]
Why the name changed
Stuppy compared seeds of plants then called Puna bonnieae and Puna clavarioides. In today's Tephrocactus bonnieae, the outer surface of the covering was smooth. In Maihueniopsis clavarioides, it consisted of flattened hairs and cells in a fibrous arrangement. Embryo shape also differed. [Stuppy 2001] [2-WWW]
The set of seed traits supported transfer of T. bonnieae to Tephrocactus. Later DNA analysis placed the species in a lineage with T. molinensis and T. recurvatus. The relationship therefore did not arise solely from similarity of habit. [Las Peñas et al. 2019] [Stuppy 2001]
Chromosomes and close relatives
The cytogenetic material had 2n = 44, a tetraploid level. Endopolyploidy was also recorded in somatic cells. The same lineage contained plants differing in root type, armament and fruit, as described in the comparative monograph of the genus. [Las Peñas et al. 2019, table 2 and fig. 2]
The names Puna bonnieae and Maihueniopsis bonnieae lead to the same profile in the atlas. The species was separated from M. clavarioides, whose similar size and geophytic habit had previously encouraged placement of both plants in one genus. [2-WWW] [Las Peñas et al. 2019] [Stuppy 2001]
Synonyms and names in the literature
Maihueniopsis bonnieae · Opuntia bonnieae · Puna bonnieae [2-WWW]