Background and aims

: Tephrocactus is a genus of Cactaceae belonging to the Opuntioideae subfamily, with most of its species endemic to Argentina. It comprises bushes with lax branches formed by globose joints, which are often fragile and detach generating new plants. Clonal reproduction is associated with the occurrence of high ploidy levels in the genus. The aim of this work was to compare morpho-anatomical traits of the epidermis and underlying tissues of Tephrocactus taxa with different ploidy levels (2n = 22, 44, 77, 88, 242 and 319) and to evaluate them in a phylogenetic context.

M&M

: The epidermis and underlying tissues of specimens were studied by means of classical histological techniques. The morpho-anatomical variables were statistically compared and mapped on the phylogeny of the genus.

Results

: The stomatal frequency, the frequency of ordinary epidermal cells, the stomatal index, and the stomata length were determined and the underlying tissues (hypodermis) were analyzed with special reference to the shape, frequency and arrangement of druses. All the variables studied showed statistically significant differences among taxa. A positive relationship was found between ploidy levels and size of all types of epidermal cells and druses.

Conclusions

: The common ancestor of the group would have small stomata, an intermediate frequency of ordinary epidermal cells, and druses in their hypodermis. The characteristics of the epidermis and underlying tissues correlate with the level of ploidy in the Tephrocactus taxa studied.