Tubercle structure and plant development
In young coryphanthas, the groove on the upper side of the tubercle may be incomplete or not yet visible. During development, the areole zone expands and the groove reaches towards the axil, the depression at the tubercle base. Spine number and arrangement also change. An adult plant may produce strong central spines that were absent in the seedling. Dicht and Lüthy's monograph documents different rates of attaining adult appearance in individual species. [Dicht and Lüthy 2005, pp. 5–12]
Identification relies on a set of traits. The 2016 morphological analysis used 467 plants examined in the field and 1373 herbarium records for 48 taxa as then circumscribed. It compared 28 traits, including 17 quantitative and 11 qualitative ones. Dimensions of different groups partly overlapped. In C. georgii, habit was also described as depending on microhabitat, with more flattened plants in exposed places and elongated ones in shade. [Vázquez-Benítez et al. 2016, pp. 24–26, 38–42]
Range and habitat diversity
In the Plants of the World Online treatment, the genus includes 43 accepted species. Its range extends from Arizona, New Mexico and Texas into Mexico. Most diversity is concentrated in Mexico. Monographic descriptions cover grassland communities, dry scrub landscapes and sites associated with forests. Individual species grow on limestone or volcanic substrates, and some have narrow associations with a particular habitat. [2-WWW] [Dicht and Lüthy 2005, POWO, 11 October 2026, monograph, pp. 3–4]
An example of habitat distinctness is C. maiz-tablasensis, described from grassy plains on gypsum substrate. C. jalpanensis grows on humus lying on limestone rocks, while the slender C. pulleineana may support its long stems against neighbouring agaves and plants of Hechtia. This diversity helps explain the different shapes of stems and roots. [Dicht and Lüthy 2005, p. 4, 58, 153, 169]
Relatedness and genus circumscription
The 2022 analysis of five chloroplast DNA regions covered 44 species termed coryphanthas in the study and 43 additional Cacteae species. Including morphological traits helped separate the main lineages. The authors obtained a coherent Coryphantha group after excluding Pelecyphora macromeris (Coryphantha macromeris in the paper). This species fell in a lineage with former escobarias and pelecyphoras. Two main lineages and seven subgroups were recognised within coryphanthas, proposed as subgenera and sections. [Sánchez et al. 2022, p. 115, 117–125, 145–149]
A complete tubercle groove, apical flower position, entire outer tepals, green fruits and flat multicellular sculpturing on the lateral seed surface formed a shared set of coryphantha traits in this analysis. Axillary glands appeared in more than one lineage. Their presence, location and seasonal activity provide information about particular groups, but a single gland alone does not establish close relatedness among all species bearing it. [Sánchez et al. 2022, p. 119–127]