Two forms of one stem. Development and species boundaries in Acanthocereus

How the growing axis changes

Stem dimorphism denotes two recognisable forms during development. In some Acanthocereus, early portions are ribbed, narrow and furnished with numerous areoles bearing small spines. Subsequent growth changes rib number and prominence, areole spacing and spine proportions. The axis remains continuous, while successive portions differ structurally. Two photographs taken from different parts of the same plant can therefore present very different outlines. Botanical documentation benefits from showing the connection between a juvenile portion and a mature branch. [Arias et al. 2005] [González-Zamora et al. 2026]

Acanthocereus paradoxus illustrates this sequence well. Its juvenile stems usually have five ribs, occasionally six, whereas adult portions are thin and cylindrical. In Acanthocereus crypticus, juvenile stems have three or four ribs and likewise pass into a cylindrical phase. Adult habit makes the species resemble one another, while the earlier stage provides a separating character. Taxonomic descriptions therefore link rib number to stem phase. Recording only one number would discard an important part of plant biology and complicate comparisons between specimens at different stages. [González-Zamora et al. 2026]

Change can accompany a stable rib number

Acanthocereus veronicae retains three ribs in both juvenile and adult stems. Areole size, the distance between areoles and the spines nevertheless change. Young spine clusters lie close together, whereas the adult stem has larger areoles more widely spaced along the ribs. Its areoles bear short central spines with swollen bases, together with radial spines. Developmental assessment thus includes proportions and surface organisation. Rib number is one descriptive element, while several characters together capture the change in the complete structure. [González-Zamora et al. 2026]

A different sequence was described in Acanthocereus lempirensis. Juvenile stems have 6–10 ribs and developed ones 3–5, retaining broad rounded ribs and a glaucous green surface. By contrast, the protologue of Acanthocereus canoensis describes its stems as monomorphic. That species maintains six or seven rounded ribs. Different species therefore exhibit different extents of change within the same taxonomic group. A generic account becomes more precise when it accommodates these clearly documented differences alongside the typical developmental pattern. [House et al. 2013] [Vega et al. 2023]

Why former Peniocereus entered Acanthocereus

Slender stems and tuberous roots long brought plants of different ancestry together in classifications. In 2005, Arias and colleagues compared chloroplast data with the structure of plants assigned to Peniocereus. The former genus separated into several lineages. Species with characteristic developmental changes in the stem appeared near Acanthocereus within Hylocereeae. Others, including the lineage containing Peniocereus greggii, remained in a separate part of the tree. Similar overall habit therefore needed to be considered together with development and evidence of relationship. [Arias et al. 2005]

Korotkova, Borsch and Arias developed this interpretation in 2017. Their treatment of Hylocereeae supported the joint placement of sampled Acanthocereus and part of the former Peniocereus. The synopsis connected accepted names, previous combinations and type material. The new combination Acanthocereus canoensis relied on morphological characters because the species lay outside molecular sampling. That detail specifies the kind and strength of the taxonomic evidence. A name change records an interpretation of relationship, while the species account retains observations made under the name used in the original study. [Korotkova et al. 2017]

One historical name and two Mexican coastal lineages

The 2026 work began with the problem of Acanthocereus rosei. Plants from Sinaloa and Jalisco bore the same name and had cylindrical adult stems, but were geographically separated. Fieldwork during 2020–2024 was combined with herbarium specimens and comparisons of vegetative and reproductive organs. Additional populations from Jalisco and Nayarit were distinctive in retaining three ribs in both stem phases. The authors assembled evidence to test whether the observed differences corresponded to separate lineages or fell within the previously recognised species. [González-Zamora et al. 2026]

The analysis used three chloroplast DNA regions, the rpl16 intron, the rpl32–trnL intergenic spacer and the ycf1 gene. The genus was represented by 14 samples. Agreement between maximum likelihood and Bayesian inference supported the recovered branching pattern. Plants identified as Acanthocereus rosei from Jalisco grouped near Acanthocereus cuixmalensis and Acanthocereus paradoxus. The Sinaloa material grouped with populations subsequently named Acanthocereus veronicae. The shared historical name therefore encompassed plants from different parts of the sampled tree. [González-Zamora et al. 2026]

The three analysed regions belong to the chloroplast genome and therefore provide linked information about one component of the plant’s hereditary material. In this study, their results were combined with morphology and geography. That scope makes clear what the tree represents and why the new species descriptions also drew on field observations. [González-Zamora et al. 2026]

A character combination that can be examined

The newly separated Acanthocereus crypticus has subtly mottled, thin cylindrical adult stems and three or four ribs on juvenile portions. Typical Acanthocereus rosei from Sinaloa is more strongly mottled and has longer scales on the part of the flower surrounding the ovary. Each character concerns a different plant structure. Their combination, together with the separate position of chloroplast DNA, supported the new diagnosis. Historical Jalisco specimens can consequently be reassessed using a defined set of characters and their geographic provenance. [González-Zamora et al. 2026]

Acanthocereus veronicae illustrates another difficulty. Its three-ribbed stem resembles Acanthocereus maculatus, but its epidermis remains uniformly coloured. In the chloroplast tree, the cylindrical-stemmed Acanthocereus rosei proved a close relative. Similarity in an identification character and the closest relationship within a particular tree can therefore direct attention to different comparisons. The authors interpreted the results as supporting parallel origins of cylindrical stems. A fuller reconstruction of that character’s history requires broader sampling, particularly of species from southern Mexico and Central America. [González-Zamora et al. 2026]

Flowers complement the stem account

Honduran evidence shows how much information flower-opening time adds. Acanthocereus canoensis has a deep pink perianth, a narrow tube and a distinct nectar chamber. Flowers remain open from before dawn into the morning. Acanthocereus lempirensis is also pink-flowered, but full opening occurs from midnight into early morning and the inner tepal tips have a different shape. Acanthocereus chiapensis has a cream-white perianth and nocturnal opening. Combining stem and floral characters clarifies similarities that can remain ambiguous when only stems are examined. [House et al. 2013] [Vega et al. 2023]

Floral structure can also suggest a functional hypothesis. The authors describing Acanthocereus canoensis linked its intense colour, narrow tube and daytime opening with possible hummingbird involvement. That hypothesis concerns a character combination, whereas a visitor’s actual effectiveness requires observations of pollen transfer and pollination outcomes. Likewise, separation in a chloroplast tree describes the history of the genomic regions analysed. Keeping the levels of observation explicit allows morphology, phenology and DNA to be used together, with each type of evidence interpreted within its demonstrated scope. [House et al. 2013] [González-Zamora et al. 2026]

Documenting the whole plant and its site

Useful identification documentation for Acanthocereus includes habit, juvenile growth, an adult stem portion and an areole close-up. A flower photographed from the side shows tube proportions, while a frontal view reveals perianth orientation. Fruits and seeds complete the reproductive character set. The 2026 comparisons followed this organisation of material. A herbarium voucher and site record allow later return to the same material even when the interpretation of its name changes. Continuity of documentation connects a morphological account with a verifiable research result. [González-Zamora et al. 2026]

Accurate identification is directly connected to range assessment. A population long included within a broadly defined species may, after revision, represent a separate local lineage. For Acanthocereus crypticus, the authors described few known sites and proposed a high threat category. The account of Acanthocereus lempirensis similarly connected morphology with limestone substrate and pressure on forest fragments. A precise species account therefore retains plant structure, the extent of population knowledge and the date of study. Subsequent observations can then be assigned to a defined taxon and compared with the earlier evidence. [González-Zamora et al. 2026] [Vega et al. 2023]