Wood Anatomy of Portulacaceae and Hectorellaceae: Ecological, Habital, and Systematic Implications

Qualitative and quantitative wood data are given for 13 species of 10 genera of Portulacaceae (secondary xylem from additional species of Anacampseros and Lewisia were studied but not quantitatively analyzed). Most Portulacaceae show modifications that can be related to the succulent habit, including wide, tall rays mostly composed of thin-walled cells; total or partial substitution of axial parenchyma for libriform fibers ; and modified patterns of pitting on lateral walls of vessels. Pseudoscalariform pitting is more common in Portulacaceae than in other dicotyledon families. In vessels of Anacampseros wood, wide helical bands of secondary wall materi al are present. Similar helices (but without the unusual width) occur in the wood of Lewisia and Heclorella. Woods of Portulacaceae as a whole are markedly xeromorphic with respect to vessel e lement dimensions, vessel density, and vessel grouping; wood of Lewisia and Hectorella is especi ally xeromorphic. Xeromorphism is not so pronounced in succulent dicotyledons at large. Woods of species of Portulacaceae with less marked adaptation to succulence show close resemblance to woods of Didiereaceae and woodier Cactaceae, suggesting the validity of the suborder Portulacineae, which includes these three families plus Hectorellaceae and Basellaceae. The wood of Heclorella is very similar to that of Lewisia rediviva and contains no features not also observed in Portulacaceae. Tracheidlike idioblasts in rays of Anacampseros are likely not homologous with wide-band vascular (or vasicentric) tracheids in fascicular secondary xylem of globular cacti. Dark-colored mucilage idioblasts in Portulacaceae are likely to be a homoplasy; they occur in a scattering of Caryophyllales