Strombocactus disciformis subsp. esperanzae

Name and occurrence

Strombocactus disciformis subsp. esperanzae Glass & S.Arias was described in 1996. POWO accepts it as a subspecies occurring naturally in Guanajuato. The former names S. pulcherrimus, Ariocarpus pulcherrimus, Pediocactus pulcherrimus and S. disciformis var. esperanzae are its synonyms. [2-WWW]

The comparative material described in 2010 came from Sierra Gorda, near Xichú, where plants grew on steep canyon walls with shale rocks. Later studies of seed development and nectaries used plants from the UNAM collection and the regional botanical garden in Cadereyta. The authors did not find specimens at the natural locality checked. This observation did not determine the entire range or abundance of the subspecies. [Arias and Sánchez-Martínez 2010, Arias and Sánchez-Martínez, p. 621. Camacho-Velázquez et al., Flora, p. 90, Botanical Sciences, p. 101] [Camacho-Velázquez et al. 2018, Arias and Sánchez-Martínez, p. 621. Camacho-Velázquez et al., Flora, p. 90, Botanical Sciences, p. 101] [Camacho-Velázquez et al. 2019, Arias and Sánchez-Martínez, p. 621. Camacho-Velázquez et al., Flora, p. 90, Botanical Sciences, p. 101]

Stem and magenta flowers

The 2010 comparison gives spherical to elongated stems, 2.5–4.5 cm tall and 4–5 cm in diameter. Areoles had 1–5 straight, flexible spines 0.8–2 cm long. They were greyish with a darker tip or dark bands. Spines fell off early. Overlapping tubercles retain the genus's characteristic scale-like arrangement. [Arias and Sánchez-Martínez 2010, p. 619–621, tabela 1]

Flowers were 2.5–3.5 cm long and 1.1–2 cm in diameter. Intense magenta colour covers both perianth and throat. Later observations showed a slightly paler shade along tepal margins and daytime flower opening. In the botanical comparison, fruits were reddish purple, 6–10 mm long and 3–4 mm in diameter, opening through a single longitudinal slit. [Arias and Sánchez-Martínez 2010, Arias and Sánchez-Martínez, p. 621, Table 1. Camacho-Velázquez et al., p. 102, Fig. 1] [Camacho-Velázquez et al. 2019, Arias and Sánchez-Martínez, p. 621, Table 1. Camacho-Velázquez et al., p. 102, Fig. 1]

The nectary and its secretion

The ring-shaped nectary surrounds the style base below attachment of the deepest stamens. Its epidermis has relatively flat cells, and the secretory parenchyma in the material studied had around 8–9 layers. Modified stomatal openings are open before full flower expansion and during nectar secretion. Deeper parenchyma links the secretory tissue to neighbouring vascular bundles. [Camacho-Velázquez et al. 2019, p. 102–104, ryc. 2–3, 5]

Nectar was collected in the botanical garden at 15 h from fifteen flowers of different individuals. The mean refractometric value was 8.65 ± 3.98°Brix. The publication did not clearly specify the dispersion-measure type. The reading made in February 2018 characterises a particular sample. The measurement did not determine sugar composition or the amount of energy supplied by the entire flower over a day. [Camacho-Velázquez et al. 2019, pp. 102–104, 107]

Seeds with an aril

In the 2018 study, seed length without the aril was 0.46 ± 0.03 mm, and with it 0.57 ± 0.04 mm. These are means ± standard deviation for 32 seeds, four from each of eight fruits. The pale aril forms through local divisions of funicular cells after fertilisation and develops tissue with large air spaces. Seeds remained at the surface for 25 days in the distilled-water experiment. [Camacho-Velázquez et al. 2018, p. 90–94, ryc. 2–4, 7]

In material obtained from hand-pollinated collection plants, mean ovule number was 933 ± 307.5, and developed seed number 596 ± 177.6. Ovule counts in ovaries and seed counts in fruits were determined in ten samples. The proportion of developed seeds relative to ovules, calculated from the means, was 63.87%. Conditions under which this material arose differed from the field samples of the other two taxa. [Camacho-Velázquez et al. 2018, p. 91, 93–94, 100]

Germination and the start of growth

On moist filter paper in dishes, at 25°C with a twelve-hour photoperiod, a mean of 92.08 ± 7.75% of seeds germinated. The value is the mean ± standard deviation of eight replicates of 30 seeds. Observation lasted 30 days, and seeds were neither scarified nor disinfected. After radicle emergence, the hypocotyl broadens, cotyledons and hypocotyl turn green, and the young spherical plant forms tubercles and areoles near the tip. [Camacho-Velázquez et al. 2018, p. 91, 94–95, ryc. 8]

The result describes germination capacity of a specific batch from a botanical collection. Subsequent seedling growth in a rocky microhabitat is a separate stage in the subspecies' biology. The basis of aril structure and comparison of sowing methods are presented in the article on Strombocactus seeds. [Camacho-Velázquez et al. 2018, pp. 90, 100]

Related articles