Strombocactus disciformis

Name and two subspecies

The accepted name is Strombocactus disciformis (DC.) Britton & Rose. The species was described in 1828 as Mammillaria disciformis, and the current combination was published in 1922. The historical names Echinocactus disciformis, Ariocarpus disciformis and Pediocactus disciformis refer to the same species in POWO. [2-WWW] [Arias and Sánchez-Martínez 2010, POWO, as of 11 October 2026. Arias and Sánchez-Martínez, p. 619]

POWO accepts subsp. disciformis and subsp. esperanzae. The names S. jarmilae and S. disciformis var. seidelii belong to the synonymy of the nominate subspecies. S. pulcherrimus is a synonym of subsp. esperanzae. Study results given with a full subspecies name can therefore be assigned to the appropriate material. [2-WWW] [2-WWW] [2-WWW]

Stem and root

The stem is greenish grey, flattened to spherical, sometimes elongated. Overlapping, leathery tubercles form a surface resembling an arrangement of scales. Flexible spines occur on younger areoles and fall off early. In the 2010 comparative material, the nominate subspecies had 1–5 spines 0.7–1.5 cm long, and subsp. esperanzae had 1–5 spines 0.8–2 cm long. Older body portions therefore remain sparsely spined. [Arias and Sánchez-Martínez 2010, p. 620–621, tabela 1]

A strong napiform root and a stem partly sunken into the substrate were described for the species. This structure differs from the superficial, fibrous root system of S. corregidorae. The difference also matters when comparing photographs of plants removed from their substrate. [Arias and Sánchez-Martínez 2010, Arias and Sánchez-Martínez, p. 620. Ivannikov et al., p. 2] [Ivannikov et al. 2022, Arias and Sánchez-Martínez, p. 620. Ivannikov et al., p. 2]

Siedlisko

The species occurs in the canyon system of Querétaro, Hidalgo and Guanajuato. Typical sites include calcareous shale, steep slopes and rock fissures containing fine soil. Stems can occur on exposed surfaces and beside plants providing partial shelter. In the 2018 study, the nominate subspecies was collected from one Querétaro locality, while subsp. esperanzae was represented by plants from two botanical collections. [Camacho-Velázquez et al. 2018, p. 89–90]

The current POWO list assigns the natural range of subsp. disciformis to Querétaro–Hidalgo and subsp. esperanzae to Guanajuato. These separate subspecies ranges are described in their own accounts. [2-WWW] [2-WWW]

Flowers and nectary

Funnel-shaped flowers open during the day near the stem tip. The nominate subspecies has a white or yellowish-white perianth and red throat. Subsp. esperanzae is distinguished by an intense magenta perianth and throat. A ring-shaped nectary lies below attachment of the deepest stamens. The secretory tissue is covered by a single-layered epidermis with open nectarostomata. [Arias and Sánchez-Martínez 2010, Arias and Sánchez-Martínez, Table 1. Camacho-Velázquez et al., pp. 102–104] [Camacho-Velázquez et al. 2019, Arias and Sánchez-Martínez, Table 1. Camacho-Velázquez et al., pp. 102–104]

In February 2018, nectar collected at 15 h from fifteen flowers of different individuals of each subspecies gave mean readings of 22.09 ± 7.42°Brix for subsp. disciformis and 8.65 ± 3.98°Brix for subsp. esperanzae. The publication gives these values with a dispersion measure indicated by ±, without clearly defining its type in the methods. The refractometer described dissolved-substance concentration. Neither individual sugar composition nor full daily nectar production was measured. [Camacho-Velázquez et al. 2019, pp. 102–104, 107]

Fruits, arils and germination

Fruits open through longitudinal slits. In the 2010 comparison, those of the nominate subspecies were 7–10 mm long and 6–7 mm in diameter, while those of subsp. esperanzae were 6–10 and 3–4 mm, respectively. Seeds in both subspecies have a pale, membranous appendage. The 2018 developmental study established that this is an aril developing from the funiculus. The older comparative description used the term strophiole. Extensive air spaces occur inside the aril. [Arias and Sánchez-Martínez 2010, Arias and Sánchez-Martínez, Table 1. Camacho-Velázquez et al., pp. 91–94, 98] [Camacho-Velázquez et al. 2018, Arias and Sánchez-Martínez, Table 1. Camacho-Velázquez et al., pp. 91–94, 98]

In controlled sowing, mean germination was 97.08 ± 3.75% in subsp. disciformis and 92.08 ± 7.75% in subsp. esperanzae. These are means ± standard deviation from eight replicates of 30 seeds per taxon. Seeds lay on moist filter paper in dishes at 25°C with 12 hours of light daily. Observation lasted 30 days, and the criterion was emergence of the radicle from the coat. The experiment documents sowing of the studied batches without scarification or disinfection. [Camacho-Velázquez et al. 2018, pp. 91, 94]

An emerging seedling has a short radicle with numerous root hairs, small cotyledons and a broad hypocotyl, the axis section below the cotyledons. The hypocotyl expands radially, forming a spherical young plant. Small tubercles and areoles later differentiate near the tip. The aril may remain on the germinating seed surface and locally deflect the emerging radicle. [Camacho-Velázquez et al. 2018, pp. 94–95, Fig. 8]

Regeneration in vitro

Ivannikov and colleagues obtained new shoots from stem fragments of seedlings raised under sterile conditions. Material was identified as S. disciformis, without a subspecies designation. Callus, proliferating regenerative tissue, was produced on modified Murashige and Skoog medium. Shoots then arose through indirect organogenesis. Cultures were maintained at 22–26°C with sixteen-hour illumination. [Ivannikov et al. 2022, pp. 2–3]

In the ninety-day experiment's table, the treatment with 1 mg/l BAP and no 2,4-D yielded 76% regenerating callus clusters and a mean of 3.7 ± 0.12 shoots per 5 × 5 mm cluster. BAP is a growth regulator in the cytokinin group. Results describe shoot regeneration from tissue in a specific laboratory system. Acclimatisation assessments pooled for the three species studied cannot be assigned as separate survival of S. disciformis. [Ivannikov et al. 2022, p. 3, tabela 2]

Pressure on natural populations

In 2014–2015, Olmos-Lau and Mandujano examined offers of Strombocactus plants and seeds in four languages. They found 32 online shops and 24 advertisements on large platforms. Some offers indicated natural localities of origin. The study concerned sales statements and documentation. It records historical commercial pressure, whose scale in 2026 was not measured in this study. [Olmos-Lau and Mandujano 2016, pp. 3–6]

Related articles

Materials from the author's archive

The species also appears in Konrad Szychowski's private material archive. [Kaktusy i Inne 2005a, file p. 37]