Four names in the current list
Plants of the World Online accepts Lophophora alberto-vojtechii, L. diffusa, L. fricii and L. williamsii. Boke and Anderson's classical 1970 studies distinguished two species, L. williamsii and L. diffusa. Northern and southern populations differed in tubercle arrangement, stem surface and pollen. This treatment was based on specific comparative material and preceded the description of miniature L. alberto-vojtechii and later treatments of L. fricii. [2-WWW][Boke and Anderson 1970, Boke and Anderson, pp. 569, 575, 577]
The introductions to two genomic articles from 2026 also refer to the former two-species picture. At the same time, the plastid analysis includes a sequence labelled L. fricii. The publication date of a DNA sequence and the taxonomic scope used in its introduction are separate pieces of information. The results of a new paper are assigned to the material actually studied, while the current name list is checked separately. [Zhang et al. 2026, Zhang et al., pp. 675, 678. Liu et al., p. 2][Liu et al. 2026, Zhang et al., pp. 675, 678. Liu et al., p. 2][2-WWW]
Species boundaries and rank
In 2009, Šnicer, Bohata and Myšák recognised five species, including L. koehresii. In POWO, this name now falls within L. diffusa. L. fricii was treated differently and is accepted as a species, although it was formerly also published as a subspecies of L. diffusa or a variety of L. williamsii. The difference in species counts results from defining their scope and rank. It does not mean that all previously described differences between plants disappear when names are combined. [Šnicer et al. 2009, Šnicer et al., pp. 296–297][2-WWW][2-WWW]
In a detailed seed description, the authors compared L. alberto-vojtechii material with L. fricii and plants now assigned to L. diffusa (L. koehresii in the paper). Seeds in the first group had convex seed-coat cell sculpture and a broad V-shaped hilum. Material labelled L. koehresii was distinguished by a more reticulate seed coat and an almost circular, open hilum. The comparison concerns this group of specimens distinguished by the authors within the current scope of L. diffusa. [Šnicer et al. 2009, pp. 296, 299][2-WWW]
The decipiens label and a formal synonym
In 2000, Hansen compared stems, flowers and seed-coat images of L. fricii with specimens described in collections as L. williamsii var. decipiens. He regarded many of the photographed plants as L. fricii. However, some seeds showed intermediate sculpture, and the origin of the specimen used in the original variety description remained unknown. The article documents variation in particular plants and proposes their identification. [Hansen 2000, pp. 228–232]
POWO places the formal name L. williamsii var. decipiens among the synonyms of L. williamsii. This entry refers the name to an accepted taxon. It does not endorse the identification of every specimen that was once assigned that epithet. For older material, collection number, origin and a full set of traits connect the label to a particular specimen. Formal synonym status and reidentification of a photographed plant describe two different relationships between name and material. [2-WWW][Hansen 2000]
The oldest description and basionym authorship
Calvo and Benítez found a French description of Echinocactus williamsii published by Jean François Cels in September 1842 in Annales de Flore et de Pomone. Authorship had usually been attributed to Salm-Reifferscheid-Dyck and dated to 1845. Cels's description was an earlier valid publication of this name. Lemaire described Echinocactus williamsianus in 1843, after Cels's description. [Calvo and Benítez 2023, pp. 1094–1095]
A basionym is an earlier name on which a new combination is based after a species is transferred to another genus. The current form is Lophophora williamsii (Lem. ex J.F.Cels) J.M.Coult. The authors in parentheses concern the basionym, while Coulter published the combination in Lophophora in 1894. The component ‘ex’ indicates that Cels validly published a name previously attributed to Lemaire. Corrected authorship changes neither the epithet williamsii nor automatically the species' biological scope. [Calvo and Benítez 2023, pp. 1094–1095][2-WWW]
The name's type and priority
No original material was found for Cels's earlier name. Calvo and Benítez designated a neotype, a specimen selected later to replace the missing original type. They chose the Mexican collection E.F. Anderson 1079 held at RSA. The same material had already been associated with later names. The shared type fixed the reference of these names to the same material. A type connects a name with a specimen, while species boundaries are established through a broader analysis of plants. [Calvo and Benítez 2023, pp. 1094–1095]
Hofer had previously proposed conserving the name based on the 1845 publication against the older E. williamsianus from 1843. Discovery of a valid 1842 publication of E. williamsii reversed this priority relationship. Calvo and Benítez considered the conservation proposal unnecessary. In their interpretation, after designation of a shared type, the later 1845 publication becomes an isonym, a subsequent reuse of the same name based on the same type, without separate nomenclatural status. A proposal to conserve a name and its formal acceptance are separate events, and the article discussed presents a solution based on the earlier description. [Calvo and Benítez 2023, pp. 1094–1095]
What DNA analysis can resolve
Zhang and colleagues' 2026 chloroplast tree united the available L. diffusa, L. fricii and L. williamsii sequences in one group. L. alberto-vojtechii was not included. High support for this group assesses the stability of the result in the sequence set used. Precise boundaries of all four species require samples from many populations, information on intraspecific variation and broader genomic comparison. [Zhang et al. 2026, pp. 676–678]
Taxonomy, nomenclature and identification use related but different data. Taxonomy defines a plant group, nomenclature establishes its name and type, and identification assigns the specimen studied to a taxon. In an experiment's description, all three elements are linked through identification of the material. A former name in parentheses, a voucher specimen number and the year of the classification used therefore help interpret a result without transferring it to other plants. [Calvo and Benítez 2023][Zhang et al. 2026][Hansen 2000]
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.
Structure, Development, and Taxonomy in the Genus Lophophora
Boke N. H., Anderson E. F., Structure, Development, and Taxonomy in the Genus Lophophora, American Journal of Botany, 1970, 57(5):569-578, doi: 10.1002/j.1537-2197.1970.tb09850.x
Studies of tubercle, areole and flower development and the anatomy of the stem surface, pollen, fruits and seeds. Anatomical material comes mainly from Lophophora williamsii from Texas. The comparison of northern and southern populations supports recognition of L. williamsii and L. diffusa in the authors' historical treatment. The relationships and hypotheses of species origins presented there are morphological interpretations from 1970.
The complete chloroplast genome sequence of Lophophora diffusa
Zhang T., Li N., Cui Z., Wang Y., Liu X., The complete chloroplast genome sequence of Lophophora diffusa, Mitochondrial DNA Part B: Resources, 2026, 11(5):675-680, doi: 10.1080/23802359.2026.2658959
Sequencing of the chloroplast genome of a Lophophora diffusa specimen using PacBio HiFi. The paper presents sequence length, strong reduction of inverted repeats, gene annotation, comparison with an earlier plastome and a tree based on shared chloroplast genes. The analysis includes available L. fricii and L. williamsii sequences, without L. alberto-vojtechii.
Assembly and comparative analysis of the first complete mitochondrial genome of Lophophora williamsii (Cactaceae)
Liu X., Zhang Y., Wang Y., Gao S., Li N., Cui Z., Zhang L., Zhang T., Assembly and comparative analysis of the first complete mitochondrial genome of Lophophora williamsii (Cactaceae), Frontiers in Plant Science, 2026, 17:1870314, doi: 10.3389/fpls.2026.1870314
The first assembly of the Lophophora williamsii mitochondrial genome from long HiFi reads. The authors analyse repeats, fragments homologous to chloroplasts, predicted RNA editing sites, codon usage, selection pressure and phylogenetic relationships. Five linear representations describe the assembly, whose dynamics in vivo require verification. The discussion separates RNA editing predictions, sequence analysis and functions that require experimental validation.
The Littlest Lophophora
Šnicer J., Bohata J., Myšák V., The Littlest Lophophora, Cactus and Succulent Journal, 2009, 81(6):294-300, doi: 10.2985/015.081.0606
An article by the authors of Lophophora alberto-vojtechii that expands on the original 2008 description. It presents the discovery, structure of underground parts and the crown, flowering, fruits, seed comparison under an electron microscope, alluvial habitat and seasonal changes in stem position. It lists new locality reports and a key to five species in the authors' treatment. Observations of insect visits and a low-temperature episode retain the scope of field reports.
Lophophora fricii Habermann und die umstrittene Varietät Lophophora williamsii var. decipiens Croizat
Hansen P., Lophophora fricii Habermann und die umstrittene Varietät Lophophora williamsii var. decipiens Croizat, Kakteen und andere Sukkulenten, 2000, 51(9):225-232
A comparison of variation in Lophophora fricii and collection specimens identified as L. williamsii var. decipiens. The author documents stems, flowers, branching and seed coat sculpture under an electron microscope. He discusses the proposed assignment of some of the studied material to L. fricii and unclear cases. The comparison includes plant photographs, seed micrographs and the history of use of the varietal name in collections.
A nomenclatural review of the name Echinocactus williamsii (Lophophora williamsii): Correct author and year of publication
Calvo J., Benítez G., A nomenclatural review of the name Echinocactus williamsii (Lophophora williamsii): Correct author and year of publication, Taxon, 2023, 72(5):1093-1097, doi: 10.1002/tax.12979
An analysis of historical publications and herbarium documentation of the name Lophophora williamsii. The authors locate a valid description of Echinocactus williamsii published by Cels in 1842, correct basionym authorship, designate a neotype and discuss priority over the name from 1843 and consequences for the earlier conservation proposal.
