Acharagma aguirreanum
Acharagma aguirreanum (Glass & R.A.Foster) Glass is a miniature cactus restricted entirely to a single canyon system in the western Sierra de la Paila, Coahuila, Mexico. Charles Glass and Robert Foster first described it in 1972 as Gymnocactus aguirreanus in volume 44 of the Cactus and Succulent Journal (Los Angeles); Glass later established the current combination in his 1997/1998 guide to threatened Mexican Cactaceae, simultaneously erecting the genus Acharagma on the basis of ungrooved adaxial tubercles, a morphological character separating this lineage from Escobaria and Coryphantha.
The specific epithet aguirreanum honours Gustavo Aguirre Benaides (born 1915), a Mexican cactus specialist from Parras de la Fuente, Coahuila, who conducted studies on the arid and semi-arid flora of the region and on the hydrography of the Parras basin. The species shares its genus with two other narrow microendemics: Acharagma roseanum, the more accessible sister species from southeastern Coahuila assessed as Vulnerable by the IUCN in 2013, and Acharagma galeanense, the Nuevo León endemic elevated to species rank by Lodé in 2017. Among the three, A. aguirreanum is the rarest, the most range-restricted, and the most sought-after by specialist collectors.
The range is extreme by any measure. The IUCN 2002 assessment by Anderson, Fitz Maurice, and Fitz Maurice documents a population of fewer than 1,000 individuals and an extent of occurrence below 1 km², making it one of the most geographically restricted cacti known. Field work by Janeba and Kalas in February 2007 confirmed Cañon Verde on the western side of the Sierra de la Paila as the type locality and corroborated the restricted population size. The sole documented threat is illegal collecting for the specialist cactus trade; the species’ extreme rarity and collector desirability make it especially vulnerable to targeted removal.
Plants occupy calcareous limestone semi-desert terrain at 1,400 to 1,600 m elevation, growing in two distinct microsite types: open limestone ridges in full sun, and shaded areas along canyon walls or under shrubs. The fleshy napiform taproot penetrates rock crevices, functioning as both a structural anchor and a water-storage organ during the dry winter season. Molecular phylogenetic work placing Acharagma in a clade with Lophophora and Obregonia is taxonomically counterintuitive given the genus’s visual resemblance to Escobaria, but is consistent with the shared taproot architecture and the limestone-scree microhabitat that all three genera occupy across the Chihuahuan Desert.
Acharagma aguirreanum quick reference
A miniature limestone-calcicole cactus from calcareous semi-desert terrain in the Sierra de la Paila, Coahuila, growing between 1,400 and 1,600 m elevation in full sun and shaded canyon-wall microsites. Values calibrated for seed grown plants in cultivation, drawn from habitat data and specialist grower experience with A. aguirreanum specifically.
Taxonomy & nomenclature
The accepted name is Acharagma aguirreanum (Glass & R.A.Foster) Glass, published by Charles Glass in his 1997/1998 Guía para la Identificación de Cactáceas Amenazadas de México (SEMARNAT/CITES), simultaneously with the erection of the genus Acharagma. The POWO LSID is urn:lsid:ipni.org:names:1029407-2. The basionym is Gymnocactus aguirreanus Glass & R.A.Foster, described in Cactus and Succulent Journal (Los Angeles) 44(2): 80 in 1972. The species passed through three additional combinations before its current placement: Thelocactus aguirreanus (Glass & R.A.Foster) Bravo (1980) and Escobaria aguirreana (Glass & R.A.Foster) N.P.Taylor (1983), published in Kakteen und andere Sukkulenten 34: 185.
The epithet aguirreanum is neuter in gender following POWO; older literature and GBIF records sometimes carry the feminine form aguirreana (as in the Escobaria aguirreana combination), a grammatical discrepancy that recurs across the species’ nomenclatural history. The name honours Gustavo Aguirre Benaides (born 1915), a Mexican cactus specialist from Parras de la Fuente, Coahuila, who studied the arid and semi-arid flora of northern Mexico and was a member of the Botanical Society of Mexico.
The genus Acharagma takes its name from Greek a- (“without”) and charakma (“groove”), identifying the defining morphological character: each tubercle lacks the adaxial groove running from apex to axil that defines Escobaria and Coryphantha. The original Gymnocactus placement in 1972 was the first step away from Escobaria on this same ungrooved-tubercle character; Glass formalized the separation as a distinct genus in 1997/1998. POWO currently accepts three species: Acharagma roseanum, A. aguirreanum, and Acharagma galeanense (Haugg) Lodé (2017). Molecular phylogenetic analysis places Acharagma in a well-supported clade with Lophophora and Obregonia, a counterintuitive result given the genus’s visual resemblance to Escobaria that had driven its historical placements across multiple genera.
A proposed taxon Acharagma huasteca based on plants from Cañon de la Huasteca, Nuevo León, appeared in discussion literature in 2011 but is absent from POWO and was not verified in peer-reviewed sources. Records from northwest of Nogales, Santa Catarina, Nuevo León, and the east side of Sierra San Marcos y Pinos are noted in specialist forums but remain unresolved as confirmed range of A. aguirreanum pending primary source verification. The POWO-confirmed distribution remains Mexico: Coahuila only.
Historical synonyms (3)
- Gymnocactus aguirreanus Glass & R.A.Foster, 1972 basionym
- Thelocactus aguirreanus (Glass & R.A.Foster) Bravo, 1980 homotypic synonym
- Escobaria aguirreana (Glass & R.A.Foster) N.P.Taylor, 1983 homotypic synonym
Sources: POWO (Kew) · IPNI · GBIF · Wikidata
Habitat
POWO records the native distribution of A. aguirreanum as Mexico: Coahuila. The type locality, confirmed by Janeba and Kalas in their February 2007 field paper, is Cañon Verde (Canyon Verde) on the western side of the Sierra de la Paila, Coahuila. The extent of occurrence is below 1 km² according to the 2002 IUCN assessment, the most restricted range of any Acharagma species and one of the smallest documented ranges of any cactus in the literature. Elevation runs from 1,400 to 1,600 m on the mid-to-upper limestone slopes of the range.
The substrate is calcareous limestone throughout: the species occupies what sources consistently describe as “calcareous semi-desert” terrain in the Sierra de la Paila. Plants grow in two distinct microsite types documented in the field literature. The first is open limestone ridges in full sun, exposed scree habitat where the taproot penetrates crevices between rock surfaces and the body is exposed to the intense UV of the 1,400–1,600 m elevation band. The second is shaded canyon walls and areas under shrubs in canyons and washes, where the plant receives filtered or dappled light rather than direct exposure. Both microsite types are confirmed from llifle field notes and explain the species’ tolerance of a relatively wide light range in cultivation.
Associated flora at the type locality includes Ariocarpus fissuratus, Astrophytum capricorne var. aureum, Epithelantha bokei, Lophophora williamsii, Mammillaria chionocephala, and Fouquieria splendens. The co-occurrence of Lophophora williamsii at the type locality is taxonomically consistent with the molecular phylogenetic evidence placing Acharagma and Lophophora in the same clade. The climate is semi-arid, Chihuahuan Desert transition zone, with summer monsoon precipitation arriving July through September and cold, dry winters; the elevation band means winter temperatures regularly fall below freezing.
Morphology
Acharagma aguirreanum is a small soft-bodied cactus, globose to depressed-globose, reaching up to 5 cm tall and 5–7 cm in diameter: wider than tall, a proportional difference from the more upright ovoid form of Acharagma roseanum. The species is typically solitary; unlike A. roseanum, which commonly clusters into groups of 3–10 heads at maturity, A. aguirreanum almost always remains as a single stem. Offsetting is documented only when the growing apex is damaged. The fleshy napiform taproot reaches considerable depth into limestone crevices and functions as both structural anchor and water reservoir.
The epidermis colour is the most immediately visible diagnostic character: medium green to distinctly blue-green or purplish-bronze, a tone that no other Acharagma species approaches. The ISI 2015 Huntington description notes “a distinctive blue-green epidermis”; llifle describes it as “medium to dark green, often tinged with bronze-rose or purple.” This blue-green to purplish cast is visible between the spine rows and is diagnosable at arm’s length in good light.
Tubercles are fleshy, pyramidal-conical, ungrooved on the adaxial face (the defining Acharagma character), approximately 5 mm long, somewhat flexible, with white wool in the axil. Radial spines number 13–16 per areole, often arranged in two series, 8–15 mm long. Colour ranges from whitish with darker tips to orange to plum-coloured but the dominant field impression is dark: brown to near-black, producing a sombre shadowed appearance unlike the pale gold blanket of A. roseanum. Central spines number 2 or more per areole, off-white to brownish-black, darkening toward the tips; centrals and radials are not dramatically differentiated in form, a genus-level character shared across all three Acharagma species.
Flowers are 18 mm long and 20 mm wide from the 1972 Glass and Foster protologue. Flower colour spans pale cream to yellowish, often with red or reddish midstripes on the outer tepals; the protologue gives “pale pink or pale ivory,” the ISI 2015 description gives “pale cream with red midstripes on the backs of the outer tepals,” and llifle gives “yellowish to reddish-yellow.” These descriptions are not mutually exclusive; within-population flower colour variation is well documented in the Escobaria alliance and all three accounts are consistent with a variable pale cream to yellowish base with reddish tepal ornamentation. Stigma lobes 5–6, yellow. Fruit greenish-purple or bronze, 12 mm long and 3.5 mm in diameter; seeds dark purplish-red to black.
Locality detail
The type locality is Cañon Verde (Canyon Verde) on the western side of the Sierra de la Paila, Coahuila, Mexico. This locality was confirmed by Janeba and Kalas in a February 2007 field visit documented in the Cactus and Succulent Journal (CSSA). The Sierra de la Paila is a relatively isolated limestone massif in central Coahuila with a peak elevation of approximately 1,780 m; the A. aguirreanum populations occupy the mid-to-upper limestone slopes at 1,400–1,600 m.
The extent of occurrence is below 1 km² according to the 2002 IUCN assessment, confirming this as one of the most geographically concentrated cactus populations on record. The Janeba and Kalas 2007 field data corroborate a population of fewer than 1,000 individuals within this area. Proposed records from northwest of Nogales (Santa Catarina, Nuevo León) and the east side of Sierra San Marcos y Pinos, including the proposed but POWO-unrecognised taxon Acharagma huasteca Elhart (2011), remain unresolved and are not treated as confirmed range extensions here.
The map plots an approximate regional centroid only. For a species with fewer than 1,000 individuals in a range of less than 1 km² and an active illegal collecting threat documented as its sole primary threat, publication of finer-grained locality data carries direct conservation risk. The centroid is placed at the resolution already available in the published IUCN assessment and the Janeba and Kalas field paper.
Cultivation
A. aguirreanum is a slow-growing limestone calcicole with two cultivation requirements that mirror its habitat directly: a mineral substrate with a meaningful limestone fraction, and a completely dry winter rest. The napiform taproot is the plant’s greatest risk factor. Under wet or cool-wet conditions in autumn, the root neck rots within days and the plant is lost. The ISI 2015 Huntington description flags the “water-sensitive nature” as the primary cultivation challenge, not sun intensity or cold. Growers already maintaining Chihuahuan Desert cacti on mineral substrates will find the requirements familiar; anyone accustomed to standard cactus compost mixes will need to adjust both the substrate recipe and the autumn watering schedule.
Substrate
A. aguirreanum is a confirmed limestone calcicole from calcareous semi-desert at 1,400–1,600 m, sharing its parent rock geology with A. roseanum in the adjacent limestone ranges of southeastern Coahuila. The working recipe uses seven components summing to 100 percent: 35% pumice (3–6 mm), 15% lava rock (scoria, 3–6 mm), 10% zeolite (clinoptilolite, 4–6 mm), 5% granite grit, 20% crushed limestone (3–6 mm), 10% coarse silica (horticultural-grade, 1–3 mm), and 5% worm castings. The 20% limestone fraction reflects the species’ strict calcicole character and the limestone scree parent rock of the Cañon Verde type locality. The organic fraction is held at 5% rather than the 10% Cactaceae baseline because the semi-arid summer-monsoon habitat with excellent rocky drainage provides very low soil organic input, and higher organic content increases moisture retention around the rot-prone taproot without habitat justification.
All three Acharagma species grow on limestone scree in the Sierra Madre Oriental foothills of Coahuila and Nuevo León. A. galeanense carries 25% limestone reflecting its confirmed high-elevation (2,650 m) pure-limestone microsite; A. roseanum and A. aguirreanum share the 20% limestone fraction from their 1,400–1,600 m and 1,100–2,100 m calcicole habitat respectively.
| Species | Pumice | Lava | Zeolite | Granite | Limestone | Silica | Organic |
|---|---|---|---|---|---|---|---|
| A. roseanum | 35% | 15% | 10% | 5% | 20% | 10% | 5% |
| A. aguirreanum (this page) | 35% | 15% | 10% | 5% | 20% | 10% | 5% |
| A. galeanense | 35% | 10% | 10% | 5% | 25% | 10% | 5% |
Watering and light
Water thoroughly from June through September, matching the summer monsoon growing season of the native habitat. Allow the substrate to dry completely between waterings. Taper sharply in October and keep the substrate entirely dry from November through March or April. Overwatering in autumn or under cool summer conditions is the most common cultivation failure mode; the taproot collapses quickly once waterlogged at low temperatures, and recovery after crown-level rot is rarely possible. First spring watering should follow visible body swelling and warming night temperatures.
Light requirement spans full sun to light shade, reflecting the dual microsite in habitat. In temperate glass-house collections, full sun from a south-facing aspect is the standard approach and suits the open-ridge microsite population. In hot inland climates where summer temperatures exceed 38°C, some midday shade protection in July and August reduces body stress without compromising spine development; this mirrors the canyon-wall microsite population’s naturally filtered exposure.
Cold tolerance extends to approximately −7°C briefly if the substrate is completely dry, consistent with the 1,400–1,600 m habitat where winter temperatures regularly fall below freezing. Wet cold at any above-freezing temperature is more dangerous than dry cold near the freezing point. In practice, maintaining above 3–5°C dry through winter eliminates cold risk entirely. Propagation is by seed only in practice; the solitary habit produces no offsets to separate under normal conditions. Germination is described as functional by specialist growers, though seed grown plants take many years to reach collector-grade character. The ISI 2015 Huntington listing noted European-cultivated strains with improved vigour, suggesting some selection is occurring within specialist collections.
Comparison
Within Acharagma’s three-species genus, Acharagma roseanum is the species most commonly confused with A. aguirreanum in cultivation. The primary field diagnostic is spine colour. A. aguirreanum presents dark brown to near-black spines giving the body a sombre, shadowed appearance at a distance; A. roseanum produces a pale gold-to-white spine blanket with a medium green epidermis. This difference is visible at arm’s length even on juvenile plants where habit-based characters are not yet developed, and it is consistent across the population rather than variable. The blue-green to purplish epidermis of A. aguirreanum, visible between the spine rows, adds a second colour diagnostic that A. roseanum never approaches.
Adult habit provides a reliable secondary diagnostic. A. roseanum commonly clusters into groups of 3–10 ovoid heads at maturity; A. aguirreanum is typically solitary throughout its life, offsetting only when crown-damaged. In cultivation where locality data has been lost, a multi-headed plant is almost certainly A. roseanum. Radial spine count reinforces this: A. aguirreanum produces 13–16 radials per areole; A. roseanum produces 15–30. The stem proportions differ too: A. aguirreanum is depressed-globose, wider than tall at up to 5 cm tall and 5–7 cm wide; A. roseanum stems are ovoid to subglobose, typically taller relative to diameter. Flower colour provides a final cross-check: pale cream to yellowish with reddish midstripes on outer tepals (A. aguirreanum) versus cream-to-pink with a bronze-rose or reddish midvein (A. roseanum), though overlap at the pale end of both ranges reduces the reliability of flower colour alone without other characters present.
Separation from Acharagma galeanense is reliable in adult plants. A. galeanense produces cylindrical stems that elongate and become prostrate with age, reaching 6–10 cm in length and forming spreading mats up to 30 cm across. A. aguirreanum remains compact and depressed-globose throughout its life. Spine colour provides a further separation: A. galeanense produces pale yellow to rich gold to dark amber spines, consistently warmer in tone than the dark brown to near-black of A. aguirreanum. In young seedlings where stem form is not yet developed, flower colour is the fastest separator: A. galeanense produces cream-yellow flowers without any pink or red component; A. aguirreanum shows the pale cream to yellowish flowers with reddish midstripes described in the ISI 2015 Huntington record. The ranges are completely disjunct: the Sierra de la Paila (A. aguirreanum) and the Galeana area of Nuevo León (A. galeanense) are separated by over 100 km.
Frequently asked questions
Is Acharagma aguirreanum hard to grow?
Intermediate to advanced. The non-negotiable requirements are a limestone-enriched mineral substrate and a completely dry winter rest from November through March. The napiform taproot is more rot-prone than that of most cacti and will fail within days if the substrate holds moisture while temperatures are cool. The ISI 2015 Huntington description identifies the species’ water-sensitive nature as the primary cultivation challenge rather than sun intensity or cold tolerance. Growers already experienced with Chihuahuan Desert species on mineral-heavy substrates will adapt most readily; anyone accustomed to standard cactus compost mixes will need to rebuild both substrate recipe and autumn watering habits before attempting this species.
Can Acharagma aguirreanum be grown from seed?
Yes, and seed is the only realistic propagation method. The solitary habit of A. aguirreanum means there are essentially no offsets to separate under normal conditions; cuttings without a stem base are not viable for this taproot-dominant species. Germination is described as functional by specialist growers at warm temperatures on a fine calcareous mix. Growth from seed is very slow; the species has remained rarer in cultivation than its sibling A. roseanum partly because of this and its water-sensitive nature. The ISI 2015 listing noted European-cultivated strains with improved vigour, suggesting some selection within established collections. Grafting onto Trichocereus or similar rootstock accelerates flowering but produces proportions inconsistent with the correct compact depressed-globose form of seed grown plants.
Is Acharagma aguirreanum legal to own?
Acharagma aguirreanum is listed on CITES Appendix II, which applies to all Cactaceae. Appendix II does not prohibit private ownership but requires export permits from Mexico and allows receiving countries to require import permits. No confirmed NOM-059-SEMARNAT-2010 listing was found in accessible sources for this species specifically; the Critically Endangered status and extreme rarity are consistent with federal protection. Nursery-propagated plants with documented artificial propagation origin are legal to buy and keep in most jurisdictions; any reputable specialist supplier will provide the required documentation. Wild-collected plants cannot obtain lawful CITES export documentation and should not be purchased.
Where does Acharagma aguirreanum grow in the wild?
On calcareous limestone terrain in the Sierra de la Paila, Coahuila, Mexico, at 1,400–1,600 m elevation. The only confirmed locality is Cañon Verde (Canyon Verde) on the western side of the range, confirmed by Janeba and Kalas during a February 2007 field visit. The IUCN 2002 assessment by Anderson, Fitz Maurice, and Fitz Maurice documents an extent of occurrence below 1 km² and a population of fewer than 1,000 individuals. Plants grow in two microsite types: open limestone ridges in full sun and shaded areas along canyon walls. Precise GPS coordinates are withheld because illegal collecting is the sole documented threat.
When does Acharagma aguirreanum flower?
Late winter to early spring in temperate cultivation, broadly February through April under glass, based on iNaturalist cultivation observations and the species’ origin in the summer-monsoon zone of Coahuila where short days and warming temperatures trigger the Escobaria-alliance genera. No specific published flowering month range exists in the accessible literature; the timing noted here is derived from cultivation records and habitat analogy. Each flower is funnel-shaped, approximately 18 mm long and 20 mm wide, pale cream to yellowish with reddish midstripes on the outer tepals in the most precise modern descriptions. A cool, dry, bright winter rest is the most reliable trigger for the following season’s flowering.
Sources & further reading
Glass, C.E. & Foster, R.A. (1972). Gymnocactus aguirreanus Glass & R.A.Foster sp. nov. Cactus and Succulent Journal (Los Angeles) 44(2): 80 · Bravo Hollis, H. (1980). Thelocactus aguirreanus (Glass & R.A.Foster) Bravo comb. nov. (combination; publication details confirmed via POWO synonymy record) · Taylor, N.P. (1983). Escobaria aguirreana (Glass & R.A.Foster) N.P.Taylor comb. nov. Kakteen und andere Sukkulenten 34: 185 · Glass, C.E. (1997/1998). Acharagma aguirreanum (Glass & R.A.Foster) Glass comb. nov. In: Guía para la Identificación de Cactáceas Amenazadas de México 1: Ac/aq. SEMARNAT/CITES · Anderson, E.F. (2001). The Cactus Family. Timber Press. ISBN 0-88192-498-9 · Anderson, E.F., Fitz Maurice, B. & Fitz Maurice, W.A. (2002). Acharagma aguirreanum. The IUCN Red List of Threatened Species 2002 (Critically Endangered; population < 1,000; EOO < 1 km²) · Janeba, Z. & Kalas, R. (2007). Acharagma aguirreanum in Sierra de la Paila. Cactus and Succulent Journal (CSSA) 79(6): 244–245. DOI: 10.2985/0007-9367(2007)79[244:AAISDL]2.0.CO;2 · ISI (2015). Acharagma aguirreanum (Glass & R.A.Foster) Glass. ISI Inventory 2015-01. Huntington Botanical Gardens, San Marino, California. HBG accession 123337 · Kew POWO (2026). Acharagma aguirreanum (Glass & R.A.Foster) Glass. powo.science.kew.org/taxon/urn:lsid:ipni.org:names:1029407-2 · IPNI (2026). Gymnocactus aguirreanus Glass & R.A.Foster. ipni.org/n/115329-2 (basionym publication details; author dates: Glass 1934–1998, Foster 1938–2002) · llifle.com (2026). Acharagma aguirreanum. Encyclopedia of Living Forms of Succulents · Wikipedia (2026). Acharagma aguirreanum. en.wikipedia.org/wiki/Acharagma_aguirreanum (etymology: Gustavo Aguirre Benaides of Parras de la Fuente, Coahuila)