Aztekium ritteri

Name and distribution

Aztekium ritteri (formerly Echinocactus ritteri) is a species accepted in POWO. The current database gives a range covering the Mexican states of Nuevo León, Coahuila and San Luis Potosí. [2-WWW]

Porembski’s classic study from 1996 associated the species with nearly vertical shale faces in the Rayones canyon in Nuevo León. On such surfaces, plants occupy small irregularities and form clusters of small stems. This describes a specific site type relevant to interpreting plant structure. Microscopic studies, however, used specimens cultivated for many years in the University of Bonn Botanical Garden, whose precise provenance was undocumented. [Porembski 1996]

A stem composed of folds

The stems described by Porembski were about 3 cm tall and 5 cm in diameter. They grew from a short taproot. Their 8–15 ribs were divided by transverse grooves, and some larger depressions branched into further crevices. Areoles on the rib crests were hairy and produced a few spines 3–4 mm long that fell off quickly. The fold arrangement therefore remains clearly visible on older stem portions. [Porembski 1996]

The main grooves were about 2–5 mm deep. In a plant measuring a few centimetres, this is a substantial fraction of the stem radius. The sculpturing increases the actual surface area roughly tenfold relative to a smooth sphere of comparable size. At the same time, about 80% of the surface lies within the shaded fold system. The directly exposed portion represents about a fifth. These values describe the geometry of the plants analysed in the study. [Porembski 1996]

Two epidermal structures on one stem

On the exposed crests, the outer wall of epidermal cells reached about 5 µm thick, and the covering cuticle about 15 µm. The cuticle forms a barrier on the cell surface. Beneath it were two or three hypodermal layers with strongly thickened, lignified walls. Almost every epidermal cell contained a druse, a cluster of calcium oxalate crystals, often occupying a substantial part of its interior. [Porembski 1996]

Deep within the grooves, the cuticle measured about 2 µm. Epidermal and hypodermal cells retained thinner walls, and the described druses were absent from the epidermis. Almost the entire population of stomatal apparatuses occurred in these sheltered zones. They were very rare on the exposed crests. Protection and gas exchange were therefore separated spatially, although both occur within a single stem. [Porembski 1996]

Hydration changes access to stomata

During dehydration, turgor and the volume of soft tissues decrease. Opposing groove walls then move closer together, concealing progressively deeper surfaces. The more strongly constructed crests remain exposed. The pathway from the stomatal apparatuses to the surrounding air becomes narrower. Porembski interpreted this change as a mechanism limiting water loss during prolonged drought. [Porembski 1996]

The description rests on tissue structure and behaviour. The study did not measure the magnitude of the decline in transpiration or the critical water loss after which the plant dies. Two levels of regulation are functionally relevant. The stomatal apparatuses themselves control pore opening, while fold geometry determines how sheltered the entire pore-bearing region is. Their interaction must be considered in relation to stem hydration. [Porembski 1996]

Light, crystals and slow growth

Shading of much of the surface also affects light availability. The author linked the species’ very slow growth to limitations on photosynthetic balance resulting from strong self-shading. This was a physiological explanation rather than the result of a direct biomass production measurement in this study. The more delicate structure of tissues hidden within the grooves may also reduce the amount of material needed to form them. [Porembski 1996]

The study also considered radiation reflection by calcium oxalate crystals and the effect of a rough surface on heat exchange with the air. These are hypotheses about additional functions of stem structure. The strongly documented result remains the distribution of crystals, wall thickenings and stomatal apparatuses, demonstrated through anatomical sections and scanning microscopy. [Porembski 1996]

Wood capable of deformation

In the comparative account of Cacteae from 2017, A. ritteri was classified among plants with wood lacking fibres and a parenchymatous cortex and pith. The wood contains vessels and wide-band tracheids. The wall thickenings of these tracheids form broad rings or helices, with thinner wall portions between them. This arrangement allows the tissue to accommodate changes in the dimensions of the hydrated stem. The authors associated this organisation with the capacity for vertical shortening during drought. [Vázquez-Sánchez et al. 2017]

Propagation from seeds and in tissue culture

David Quail described growing A. ritteri seedlings in covered containers under artificial light, with substrate moisture maintained. In his account from 1997, small seedlings remained in their original container for a long time, limiting root damage during pricking out. A photograph documented plants 18 months after sowing. A porous substrate and separation of Aztekium from faster-growing species allowed further growth without shading by neighbours. This is documented practice from a specific collection. [Quail 1997]

Production of new shoots was also studied in vitro. Corneanu et al. used rib fragments taken from small stems of the mother plant and from material previously multiplied in culture. The response depended on the medium. Callus, shoots or rooting plants formed. Transfer from medium to greenhouse required a separate acclimatisation stage. The study documents the regenerative capacity of A. ritteri tissues and distinguishes shoot production from obtaining an independent plant with roots. [Corneanu et al. 1995]

Related articles

Materials from the author's archive

The species also appears in Konrad Szychowski's private material archive. [Kaktusy i Inne 2005a, file p. 31, 32, 57] [Kaktusy i Inne 2006b, file p. 15]