Origin and surface structure
Opuntia microdasys is an accepted species native to Mexico, associated with dry scrub and desert areas. It has the habit of a low shrub or subshrub. The name was published in its current combination in 1837. [2-WWW]
On the flattened segments, clusters of small glochids form regularly spaced areoles. In the material studied microscopically, each glochid was conical, with longitudinal grooves and microbarbs, accompanied by dense hairs at its base. The surface changed gradually along the organ’s axis. Its individual regions participated in successive stages of droplet collection. [Ju et al. 2012]
How a droplet moves towards the areole
Small fog droplets settled on the glochids and their barbs, then merged into larger ones. The conical geometry creates a capillary pressure difference between the narrower and wider parts of a droplet. Together with directional grooves and changing wettability, this favours water movement towards the broader base. [Ju et al. 2012]
In the study from 2012, movement towards the base was also observed when the glochid was positioned so that gravity opposed it. Water reaching the dense hairs was rapidly drawn into their porous structure. This allowed further droplets to be collected on the exposed part of the surface. [Ju et al. 2012]
What the experiment covered
The authors used cultivated plants, electron microscopy and a controlled stream of fog generated from purified water. The study demonstrated the operation of the surface system and its individual components. The contribution of this pathway to the annual water balance of Mexican populations remains a separate question for field research. [Ju et al. 2012]
Terminologia starszej pracy
The article used the English term spines. The description concerns the small, barbed elements of the areole, discussed here as glochids. The same level of structure was later studied in O. stricta, where comparison with longer, smooth spines shows the importance of surface microsculpturing particularly clearly. [Ju et al. 2012] [Masrahi 2020]
Materials from the author's archive
The species also appears in Konrad Szychowski's private material archive. [Cactáceas y Suculentas Mexicanas 1959, file p. 24]
Synonyms and names in the literature
Cactus microdasys [2-WWW]