Ferocactus(Cactaceae) epidermis: its systematic value1

Abstract

The stem epidermis of 23 species and three subspecies of Ferocactus Britton & Rose from the tribe Cacteae-Cactaceae are described and compared using scanning electron and light microscopy. Epidermal-hypodermal samples were removed, prepared for observation, and analyzed using a similarity method. Our observations showed that most epidermal cells had an elongate-tetragonal outline with straight anticlinal walls. However, S and U-undulated anticlinal walls occurred in F. glaucescens (DC.) Britton & Rose and F. peninsulae (Engelm. ex F.A.C. Weber) Britton & Rose (Cactaceae). The microrelief of the anticlines was flat and inconspicuous or striate. The periclinal wall relief varied from none to rugose or verrucose among species; 89% of the studied species had slightly sunken or sunken parallelocytic stomata with 2 or 3 pairs of subsidiary cells. Cuticle thickness varied from 2.54 µm in F. histrix (DC.) G.E. Linds to 39.74 µm in F. flavovirens (Scheidw.) Britton & Rose and their thickness is not related to environment. Silica bodies in the hypodermis cell lumina are present in 90% of the species studied. The epidermal characters of the Ferocactus species have been described in other members of Cactoideae, none of them can be postulated as possible synapomorphies to the genus level. Pustules, which are a cutin accumulations on the outer epidermal walls are distinctive feature of F. emoryi (Engelm.) Orcutt, and here are described for the first time for the Cactaceae. The phenogram revealed three groups, and F. haematacanthus (Salm-Dyck) Bravo was revealed as the most distinct species within the genus as well as F. histrix. Both were the early derived species in the most recent phylogeny. A combination of epidermal characters can help to distinguish some Ferocactus species, but failed to support the infrageneric classifications. However, some groups of species based on their epidermal similarities agree with some clades in the most recent phylogeny.