Why genus assignments change
Tuberculate stems, spines in areoles and similarly structured flowers occur in several closely related cactus lineages. Sequence analyses can test whether species grouped in a genus form a common lineage containing all descendants of their ancestor. Establishing the name of this lineage then requires identifying the type species of the genus. The type is a fixed nomenclatural reference, while group boundaries may be updated as research results emerge. [Breslin et al. 2021, pp. 308–310, 314–316]
In 2021, Breslin, Wojciechowski and Majure reconstructed relationships in the mammilloid clade using the large single-copy region of the plastid genome. The study included 88 samples representing 78 taxa and three tree-analysis methods. The authors demonstrated the multiple lineages within broadly circumscribed Mammillaria and proposed new boundaries for the main genera. Some smaller groups required denser species sampling. [Breslin et al. 2021, pp. 310–316]
Oehmea. A reference point from 1951
Buxbaum established Oehmea in 1951, basing the name on the taxon called O. nelsonii. This taxon is now included in O. beneckei (formerly Mammillaria beneckei). Large, unevenly sculptured seeds and floral characters are important in the history of the genus. Linking the name to its type allows the appropriate application of Oehmea to be considered when further studies reveal relationships with other species. [Breslin and Majure 2026]
In the 2021 tree, Oehmea sphacelata (then studied as Mammillaria sphacelata) formed a sister lineage to the other sampled Coryphantha. The authors emphasised the distinctness of the morphological group with tubercles lacking the typical longitudinal groove and the need to investigate its remaining species. One sampled representative signalled an interesting relationship. The full boundaries of this group remained to be determined. [Breslin et al. 2021, pp. 315–316]
In the 2023 analysis by Chincoya and co-authors, sequences of 52 chloroplast loci represented 103 taxa. Oehmea beneckei (called Mammillaria beneckei in the paper), Mammillaria napina and M. zephyranthoides appeared in one of the lineages of broadly circumscribed Mammillaria. The arrangement of lineages in this paper differed in part from the 2021 results. Both studies are based on plastids, but have different taxonomic samples and analytical scopes. The 2023 authors themselves call for further determination of genus boundaries. [Chincoya et al. 2023, pp. 3–8, 12–14]
Accepted names and the 2026 expansion
| Name accepted in the atlas | Name in older accounts | Context |
|---|---|---|
| Oehmea beneckei | Mammillaria beneckei | Accepted by POWO. Buxbaum's 1951 combination. |
| Oehmea sphacelata | Mammillaria sphacelata | Accepted by POWO. Guiggi's 2022 combination. |
| Oehmea tonalensis | Mammillaria tonalensis | Accepted by POWO. Guiggi's 2022 combination. |
| Mammillaria napina | Mammillaria napina | 2026 proposal. Oehmea napina. |
| Mammillaria zephyranthoides | Mammillaria zephyranthoides | 2026 proposal. Oehmea zephyranthoides. |
In 2026, Breslin and Majure published Oehmea napina (J.A.Purpus) P.B.Breslin & Majure and O. zephyranthoides (Scheidw.) P.B.Breslin & Majure. These are combinations created by transferring previously described species to another genus. The POWO classification adopted in the atlas retains the names Mammillaria napina and M. zephyranthoides as of the verification date. The older and proposed names can thus be unambiguously linked to the same biological material. [Breslin and Majure 2026]
The three already accepted Oehmea species have different ranges. O. beneckei covers western and central Mexico, O. sphacelata occurs in Puebla and Oaxaca, and O. tonalensis in Oaxaca. Breslin and Majure draw attention to the predominantly tropical Mexican character of the proposed group. Floristic data for O. sphacelata also indicate oak forests, seasonally deciduous tropical forests and dry scrub on calcareous substrates. [Arias et al. 2012, pp. 114–119]
[2-WWW][2-WWW][2-WWW][2-WWW][2-WWW]Neobesseya and the northern cactus group
In the same 2026 paper, the authors propose reinstating Neobesseya, a genus established by Britton and Rose in 1923. Its nomenclatural reference is Neobesseya missouriensis. The proposed lineage also includes taxa transferred as N. alversonii, N. chlorantha, N. macromeris and N. vivipara. These are names from the proposal discussed, requiring links to the current profiles of these plants. [Breslin and Majure 2026]
The authors describe the newly circumscribed Neobesseya as a predominantly northern group, and the retained, narrower Pelecyphora as associated mainly with the central Chihuahuan Desert. They also indicate that the type species of historical Escobaria, now Pelecyphora tuberculosa, remains in the Pelecyphora lineage. Application of each name therefore depends on the position of its type, and the group boundaries provide the justification for the proposed combinations. [Breslin and Majure 2026]
Historically, Neobesseya was distinguished by red globose fruits and black, pitted seeds with a white aril, compared with fruits and seeds of Coryphantha. Breslin and Majure note that N. vivipara in their proposal has characters closer to the traditional diagnosis of Coryphantha. This means that the diagnostic value of individual characters needs to be assessed on a complete tree and broader material, taking their variation and evolutionary history into account. [Breslin and Majure 2026]
In current POWO, Neobesseya is a synonym of broadly circumscribed Pelecyphora. The taxa covered by the 2026 proposal are accepted as Pelecyphora alversonii, P. chlorantha, P. macromeris, P. vivipara and P. missouriensis. The atlas retains these names and presents the new combinations in Neobesseya as the separate treatment of Breslin and Majure. [2-WWW][Breslin and Majure 2026]
Scope of the evidence published in the short paper
The 2026 article is a two-page nomenclatural publication. The authors refer to strongly supported clades from their own research, for which a fuller publication is announced. In this note, they present combinations, historical types and morphological and geographical justification. The detailed data matrix, complete tree and support parameters of the new analyses belong to the forthcoming account. [Breslin and Majure 2026]
Reading the literature therefore involves three related pieces of information. These are the name used for the material in a publication, the formally published combination and the classification currently accepted in the atlas. Linking historical and current names maintains continuity of biological descriptions and allows older papers to be found when genus boundaries change. [Breslin and Majure 2026]
Genus and species profiles
Nomenclatural Changes in Mammillaria and Pelecyphora: Repopulating Oehmea and Neobesseya
Breslin P. B., Majure L. C., Nomenclatural Changes in Mammillaria and Pelecyphora: Repopulating Oehmea and Neobesseya, Haseltonia, 2026, 33(1):e331, doi: 10.2985/026.033.0101
The nomenclatural note expands Oehmea to include the species napina and zephyranthoides and proposes reinstating Neobesseya. The authors publish four new Neobesseya combinations and refer to type species, historical fruit and seed traits and the geographical distinctness of lineages. The rationale cites earlier phylogenies and announced fuller results of their own phylogenomic analysis.
Molecular phylogeny of the Mammilloid clade (Cactaceae) resolves the monophyly of Mammillaria
Breslin P. B., Wojciechowski M. F., Majure L. C., Molecular phylogeny of the Mammilloid clade (Cactaceae) resolves the monophyly of Mammillaria, Taxon, 2021, 70(2):308-323, doi: 10.1002/tax.12451
A reconstruction of mammilloid clade phylogeny from the large single-copy region of the plastid genome, using maximum likelihood, maximum parsimony and Bayesian inference. The sample contains 88 specimens representing 78 taxa, and the analysis is supported by morphological character state reconstructions. The authors propose new boundaries for Mammillaria, Cochemiea and Coryphantha and discuss the separate position of Mammillaria sphacelata, now Oehmea sphacelata.
Phylogenomics and Biogeography of the Mammilloid Clade Revealed an Intricate Evolutionary History Arose in the Mexican Plateau
Chincoya D. A., Arias S., Vaca-Paniagua F., Dávila P., Solórzano S., Phylogenomics and Biogeography of the Mammilloid Clade Revealed an Intricate Evolutionary History Arose in the Mexican Plateau, Biology, 2023, 12(4):512, doi: 10.3390/biology12040512
An analysis of 52 plastid loci from 142 chloroplast genomes representing 103 taxa in the mammilloid clade. The authors reconstruct phylogenetic relationships, lineage divergence times and historical distribution using the Dispersal–Extinction–Cladogenesis model. The paper discusses nine main lineages, variation within broadly defined Mammillaria, the position of Mammilloydia candida material with Mammillaria albiflora and the need for further assessment of generic boundaries.
Plants of the World Online — Royal Botanic Gardens, Kew
Accepted names, synonyms and distribution. A citation beside a taxon leads to its record.
Accessed 2026-10-08.
Cactaceae
[Arias S., Gama-López S., Guzmán-Cruz L. U., Vázquez-Benítez B., Cactaceae, Flora del Valle de Tehuacán-Cuicatlán, fascículo 95, Universidad Nacional Autónoma de México, Instituto de Biología, 2012, s. 1–235, wyd. 2]
The regional cactus flora of the Tehuacán-Cuicatlán valley contains keys, morphological descriptions, nomenclatural types, herbarium specimens, habitats and phenology. The treatment of Mammillaria sphacelata, now Oehmea sphacelata, presents stem and spine variation, flower, fruit and seed structure, and diagnoses of subspecies sphacelata and viperina. It gives limestone habitats in oak forests, seasonally leafless tropical forests and dry scrub.
