“…It has been hypothesized that the evolution of succulent growth form was greatly influenced by internal anatomical novelties in the stem, particularly those of the wood (Altesor et al, 1994 ; Carlquist, 2001 ; Mauseth, 2006 ). Such features involve an increased capacity of wood for water retention (Mauseth, 2006 ), very specialized tracheary elements with a limited secondary cell wall extension (Figure 1 ; Carlquist, 2001 ; Terrazas and Mauseth, 2002 ; Grego-Valencia et al, 2015 ; Reyes-Rivera et al, 2017 ) and a decreased lignification rate, which translates into a low wood accumulation (Altesor et al, 1994 ; Reyes-Rivera et al, 2017 ). Some of these characteristics are more or less conspicuous depending on the phylogeny: in Opuntioideae and Cactoideae, two of the most recently derived subfamilies with a predominance of succulent forms, diverse wood configurations have been reported (cambial variants sensu ; Carlquist, 2001 ).…”