Coryphantha robustispina

Structure and identification

The monograph distinguishes the western nominate group, often with a thick hooked central spine, from groups termed scheeri with more slender tubercles and thinner spines. Stems are spherical, ovoid or short-cylindrical, solitary or offsetting. Flowers are yellow, sometimes brownish at the tepal bases. Small glands may be hidden in groove wool, making them hard to notice in older descriptions. [Dicht and Lüthy 2005, p. 47–51]

Habitat and variation

The species occupies varied habitats in northern Mexico and in Arizona, New Mexico and Texas. The monograph describes plains, gentle foothills and flat summits in semi-desert grassland communities. A later population study also covered alluvial substrates and various shrub communities. The precise scope of each geographical group was presented in the 2013 study. [Dicht and Lüthy 2005, p. 47–51; 2013, p. 985–988] [Baker and Butterworth 2013, p. 47–51; 2013, p. 985–988]

Population variation and subspecies boundaries

Baker and colleagues compared the morphology of C. robustispina and C. poselgeriana with an analysis of variation in ISSR DNA markers. Stem measurements covered 638 plants of both species in total, and the marker study covered 204 samples of both species. Stem size, tubercle and spine length, and spine number varied in C. robustispina across its broad range. Neighbouring populations usually showed greater genetic similarity than distant ones. [Baker and Butterworth 2013, p. 986–989, 992–996, tab. 2]

The traditionally distinguished subspecies robustispina, scheeri and uncinata did not form clearly separated groups in the analyses used. The authors assessed variation as largely geographically continuous and proposed abandoning these subspecies. The comparison concerns the morphological traits and markers used. The distinctness of C. poselgeriana was much clearer than the division among populations of C. robustispina itself. [Baker and Butterworth 2013, p. 994–996]

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