Gymnocalycium horstii is the largest Gymnocalycium species, a glossy-bodied Brazilian giant from the pampa grasslands of Rio Grande do Sul. Its satiny white-to-pink funnel flowers reach 11 cm across and rank among the biggest produced by any member of the genus. IUCN Endangered; CITES Appendix II. Native to rocky sandstone outcrops in the Camaqua Basin; the buenekeri subspecies relationship is actively contested in the literature.
Gymnocalycium buenekeri is a rare flat-bodied cactus endemic to the sandstone outcrops near São Francisco de Assis, Rio Grande do Sul, Brazil. Its matte dark-green epidermis and invariably pink flowers separate it instantly from its glossy white-flowered sister taxon Gymnocalycium horstii. Classified as Endangered by IUCN; fewer than 500 plants remain in three small wild populations on private grazing land. CITES Appendix II.
Moon cactus (Gymnocalycium mihanovichii) is the Paraguayan Chaco species behind the global moon cactus trade, its chlorophyll-free color mutants grafted onto green rootstocks in nurseries worldwide. The wild type is a small flat-globose plant with distinctive horizontally banded grey-green ribs, semi-closed pale yellow flowers, and strong drought tolerance once established. Native to Argentina and Paraguay; IUCN Least Concern (2022); CITES Appendix II. Parent species to f. rubra and f. variegata.
Ariocarpus retusus subsp. furfuraceus is the northern Mexican form with equilaterally triangular, mealy-surfaced tubercles. Coahuila and Nuevo León limestone scrub, autumn-flowering, CITES Appendix I. Identification, taxonomy, and care for seed grown collector plants.
Ariocarpus retusus f. cristata is the crested fasciated form of A. retusus, rare in habitat and propagated almost entirely by grafting in cultivation. Care guide for grafted and degrafted cristate plants, with CITES status and the cresting biology that produces the fan-shaped growth.
Ferocactus glaucescens is a globose to short-cylindrical barrel cactus endemic to the limestone hills of Hidalgo and Querétaro, central Mexico. Its blue-green glaucous body, 11–15 prominent ribs, and pale yellow spines distinguish it at a glance. Lemon-yellow flowers appear in late spring. CITES Appendix II; the spineless cultivar f. inermis is a separate horticultural selection with no wild counterpart.
Ferocactus hamatacanthus is the most cold-tolerant Ferocactus, hardy to about −10°C dry, and the only species in the genus with consistently hooked central spines. Native to the Chihuahuan Desert of Texas, New Mexico, and northern Mexico (Chihuahua, Coahuila, Tamaulipas, Nuevo León), it bears large fragrant yellow flowers with scarlet centers from June through August. Two subspecies are recognized: the nominate hamatacanthus and the smaller subsp. sinuatus of South Texas and Tamaulipas.
Ferocactus viridescens is a compact, globose barrel cactus native exclusively to coastal San Diego County, California, and adjacent northern Baja California. Rarely exceeding 30 cm tall, it bears 13–21 blunt ribs armed with red-banded spines that fade to gray. Chartreuse to greenish-yellow flowers appear in spring. CNPS rank 2B.1 (seriously threatened in California); protected under the San Diego MSCP.
Ferocactus cylindraceus is the dominant barrel cactus of the Mojave and Sonoran deserts, ranging from southern California through Nevada, Arizona, Utah, and into Baja California and Sonora. Stems reach 3 m tall and 50 cm wide with 18–31 ribs; red to yellow spines densely obscure the green body. Commonly called the compass barrel or miner’s compass, it is the species most often misidentified as Ferocactus wislizeni. Protected across its US range; collection without permits is illegal.
Curator reference for Aztekium ritteri: a gypsum-cliff endemic from the Sierra Madre Oriental of Nuevo León, Mexico, carrying CITES Appendix I status and IUCN Least Concern. Taxonomy, habitat, morphology, identification against A. hintonii, and cultivation notes for serious collectors.
