Chemical composition and cellular structure of ponytail palm (Beaucarnea recurvata) cork

Ponytail palm (Beaucarnea recurvata Lemaire) is a succulent plant indigenous to Mexico frequently used as an ornamental plant throughout the world. The mature trees develop a thick corky outer bark that was studied here for the first time and compared with cork of Quercus sober Linnaeus (cork oak) and other species. The anatomical structure of ponytail palm cork showed a typical honeycomb structure in the tangential section and a brick-wall layer in the transverse section. The cells were larger and had thicker cell walls than those of Q. suber cork. Ponytail palm cork had a distinct growth ring pattern but the cell wall undulation lacked the regular wave pattern as in Q. suber cork. Fiber-like cellular structures were present protuberating from the lenticular channels. Ponytail palm cork chemically differs from Q. suber and other corks by a much lower content of suberin and enhancement of the lignocellulosic nature (18.2% extractives, 11.8% suberin, 29.7% lignin and 39.0% polysaccharides). Although in general similar to that of Q. suber cork, suberin composition of ponytail palm cork has specific features namely regarding the ratio of alpha,omega-diacids and omega-substituted hydroxyacids and presence of higher amounts of alkanoic acids. The lignin of ponytail palm cork is a HGS-type of lignin (1:12:5) with a S/G ratio of 0.4. These results add to data showing that monomeric composition of suberin and lignin of corks are species' specific. The lipophilic extractives included mainly saturated alkanoic acids and sterols while the polar extractives showed overall low amount of phenolics and unremarkable antioxidant properties.