Strombocactus disciformis subsp. disciformis

Name and range

Plants of the World Online accepts Strombocactus disciformis subsp. disciformis as a subspecies with a natural range from Querétaro to Hidalgo. The former names S. jarmilae, S. disciformis subsp. jarmilae, var. seidelii and S. turbiniformis belong to its synonymy. Subspecies esperanzae remains a separate accepted taxon. [2-WWW] [2-WWW]

Body, spines and fruits

The 2010 morphological comparison describes a spherical, flattened or basally narrowing stem, less often cylindrical, 3–12 cm high and 3–9 cm in diameter. Areoles produced 1–5 flexible spines 0.7–1.5 cm long, straight to curved, greyish with a darker tip. Spines fell off early. Flowers were 2.6–3.2 cm long and 2–3.2 cm in diameter. [Arias and Sánchez-Martínez 2010, p. 621, Table 1]

The perianth is white to yellowish white, and the throat red. Fruits 7–10 mm long and 6–7 mm in diameter change from green to reddish brown with a magenta tint. They usually split in two to four longitudinal places. These features come from the botanical comparison and serve to identify material. [Arias and Sánchez-Martínez 2010, p. 621, Table 1]

Nektarnik kwiatu

In the daytime-open, funnel-shaped flower, the nectary forms a ring around the style base. Its epidermis has slightly convex cells. Beneath it, researchers saw around 10–12 layers of secretory cells, with larger parenchyma cells associated with vascular bundles deeper inside. Nectar leaves the tissue through nectarostomata. The stated thickness concerns the histological material studied. [Camacho-Velázquez et al. 2019, p. 102–104, ryc. 2–4]

Nectar collected in the botanical garden in February 2018 had a mean reading of 22.09 ± 7.42°Brix. The sample comprised 15 flowers from different individuals, collected at 15 h. The dispersion-measure type was not clearly specified in the methods. Refractometry characterises dissolved substances in the secretion, while identifying individual sugars was left for further study. [Camacho-Velázquez et al. 2019, pp. 102–104, 107]

Seeds and seedlings

Seeds have a pale aril and a coat with distinctly convex outer cells. In the 2018 measurement, their length without the aril was 0.41 ± 0.02 mm, and with it 0.53 ± 0.04 mm. These are means ± standard deviation for 32 seeds, four from each of eight fruits. The funiculus-derived aril contains parenchyma with air spaces. This structure distinguishes seeds of both S. disciformis subspecies from the aril-free seeds of S. corregidorae. [Camacho-Velázquez et al. 2018, p. 90–93, ryc. 2–7]

Seed potential was assessed in fifteen samples by counting ovules in ovaries and developed seeds in fruits. Mean ovule number was 1035 ± 253.3, and developed seeds per fruit 768 ± 258.4. The proportion calculated from the means was 74.20%. Plants of the nominate subspecies were studied at a natural locality in Querétaro. Comparison with hand-pollinated material of subsp. esperanzae therefore involves different seed-formation conditions. [Camacho-Velázquez et al. 2018, pp. 90–91, 93–94, 100]

Eight replicates of 30 seeds on moist filter paper yielded 97.08 ± 3.75% germination at 25°C with 12 hours of light. Seeds were observed for 30 days without scarification or disinfection. The emerging seedling develops a broad hypocotyl and numerous root hairs on its short radicle. Small tubercles and areoles then appear near the tip. The germination study does not determine year-round temperatures for cultivation of adult plants. [Camacho-Velázquez et al. 2018, p. 91, 94–95, ryc. 8]

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