Growth form and habitats
Opuntia robusta is an accepted species native to Mexico. POWO describes it as a succulent shrub or tree of dry scrub. Studies in Hidalgo included plants with thick, glaucous segments, yellow spines and yellow flowers with a green stigma. The populations studied also included spreading plants growing low to the ground. [2-WWW] [Mendoza-Reyes et al. 2026]
The two populations compared in the study from 2026 were about 6 km apart. Matías Rodríguez was surrounded by pine-oak forest, while San Nicolás Tecoaco was in dry scrub. This small geographical distance coincided with variation in reproductive traits, emphasising the importance of material provenance when interpreting results. [Mendoza-Reyes et al. 2026]
Nectar-secreting spines
Extrafloral nectaries develop in the areoles of young segments as modified spines. They have a meristematic region at the base, an elongating part and an apical secretory region. Their surface consists of cells with a thin, folded cuticle. No vascular bundles or stomatal apparatuses were found inside the nectary. [Sandoval-Molina et al. 2018]
The secretory cells contain numerous mitochondria, elements of the endoplasmic reticulum, Golgi apparatuses and vesicles. As the spines mature, they lignify and secretion ceases. Ants of the genera Camponotus and Forelius visiting the nectaries were observed especially on younger segments. The study documents this interaction but does not measure its effect on plant survival. [Sandoval-Molina et al. 2018]
Sexual organization of the population
The literature describes hermaphroditic and trioecious populations, the latter including male, female and hermaphroditic plants. In the experiment published in 2026, however, all plants used for pollination manipulations were hermaphroditic. In San Nicolás Tecoaco, previously described as a trioecious population, the female individuals known to the authors did not flower during the experimental season. [Mendoza-Reyes et al. 2026]
Pollen release in the flowers preceded full stigma receptivity. This protandry establishes the sequence of male and female functions while allowing them to overlap in time. The treatments compared were isolated flowers left unmanipulated, hand self-pollination, cross-pollination, supplementary pollination of open flowers and natural pollination. [Mendoza-Reyes et al. 2026]
Seeds and variation in responses
In both populations, autonomous self-pollination produced seeds capable of germination. No reduced response after self-pollination was detected in the early reproductive stages studied. Measurements covered seeds and their germination. Following offspring survival to reproductive age would require longer observation. [Mendoza-Reyes et al. 2026]
The Matías Rodríguez population produced more ovules, while the probability of seed germination was higher in material from San Nicolás Tecoaco. Seeds were studied after scarification under controlled laboratory conditions. The result describes their response in that experiment, while field recruitment also depends on microsite availability and seedling survival. [Mendoza-Reyes et al. 2026]
Materials from the author's archive
The species also appears in Konrad Szychowski's private material archive. [Cactáceas y Suculentas Mexicanas 1959, file p. 17]