Thelocactus leucacanthus

Current treatment and schmollii material

The accepted name is Thelocactus leucacanthus (Zucc. ex Pfeiff.) Britton & Rose. POWO includes T. leucacanthus subsp. schmollii and T. ehrenbergii in the species, among others. The division into the yellow-flowering nominate subspecies and violet-flowering schmollii is retained when indicating research material. Not all local results apply to every population of the more broadly accepted species. [2-WWW]

The reproductive biology study was conducted in 2018 in La Estación, in the municipality of Peñamiller, Querétaro, at 1290 m. Plants from this population, described as T. leucacanthus subsp. schmollii, formed stem clusters and flowers in shades from violet to carmine. [Delgado-Ramírez et al. 2021, p. 792–795]

One-day flowers and phase sequence

For 30 flowers, mean length was measured as 36.04 ± 4.02 mm and diameter as 51.21 ± 11.67 mm, with standard deviations reported. Observations of 27 flowers showed anthesis approximately from 10:30 to 15:00. Pollen was released from the start of opening, and stigma lobes became receptive later. Phases partly overlapped, which the authors termed incomplete protandry, the earlier maturity of the flower's male part. [Delgado-Ramírez et al. 2021, p. 795–797, tabela 1, ryc. 2]

Pollination treatments and seeds

In May 2018, fruits formed from all 30 openly pollinated flowers and all 29 flowers manually pollinated with a mixture of foreign pollen. None formed from 24 manually self-pollinated flowers, 15 covered flowers retaining their own anthers, or six covered flowers after anther removal. The design included 10, 10, 8, 5 and 3 plants, respectively. The result supports this population's dependence on pollen from other individuals for reproduction. [Delgado-Ramírez et al. 2021, p. 793–794, 796–798, tabela 2]

Fruits were collected about 45 days after treatment. Natural pollination yielded a mean of 65.76 ± 25.42 seeds per fruit, and manual cross-pollination 61.52 ± 45.19, expressed as means ± standard deviation. The difference was not significant in the test used. Separately assessing pollen limitation would require adding pollen to flowers remaining in natural contact with visitors. [Delgado-Ramírez et al. 2021, p. 794, 798–800, tabela 2]

Pollen, bees and a small nectary

Over 55 hours of observation in May, June and October, the most frequently recorded visitors were Lasioglossum of subgenus Dialictus, Pseudopanurgus and Exomalopsis. Bees touched stamens and the stigma while collecting pollen. Diadasia was less frequent but carried much pollen of the species. Visit frequency and body pollen load describe different components of a visitor's potential effectiveness. [Delgado-Ramírez et al. 2021, p. 794–797, 799–800, ryc. 3]

At the hypanthium base, below the lowest stamens, a ring-shaped nectary with stomata and small secretory cells was identified. Histochemistry revealed starch, polysaccharides and proteins. The amount of secretion was too small to collect with the 10 µl capillary vessel used. Pollen remained the main observed reward for bees. [Delgado-Ramírez et al. 2021, p. 795–797, 800–802, ryc. 4]

The species' modelled niche

Mosco's model for the species was built from 73 records. Isothermality had a permutation importance of 66%, and precipitation seasonality 17.9%. Estimated niche breadth was 0.050. The regional modelling dataset has a broader scope than the single population in the pollination experiment. Isothermality is the ratio of mean daily temperature range to annual range, multiplied by 100. [Mosco 2019, p. 3–6, tabele 1–2]

Related articles

Materials from the author's archive

The species also appears in Konrad Szychowski's private material archive. [Kaktusy itd. 2008, file p. 2]