Abstract
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.
Highlights
The present paper continues a series of studies on wood anatomy of Caryophyllales (Centrospermae of earlier authors) begun with a survey of woods of Caryophyllaceae (Carlquist 1995a)
Little seasonal fluctuation in diameter of secondary xylem cells is visible in transections of wood of Portulacaceae (Fig. 1, 15, 19, 23, 27)
A small amount of cell diameter fluctuation is shown for a Talinum paniculatum stem in which two years of secondary xylem accumulation are present (Fig. 10); a little narrowing in the libriform fibers gives evidence that the bottom quarter of the photograph represents the first year of xylem accumulation
Summary
Qualitative and quantitative wood data are g iven for 13 species of 10 ge nera of Portulacaceae (secondary xylem from additional species of Anacampseros and Lewisia were studied but not quantitatively analyzed). In vesse ls of Anacampseros wood, wide helical bands of seco ndary wall materi a l are present. Similar he lices (but without the unusual width) occur in the wood of Lewisia a nd Heclorella. Woods of species of Portulacaceae with less marked adaptation to succulence show close rese mblance to woods of Didiereaceae a nd woodier Cactaceae, suggesting the validity of the suborder Portul ac ineae, which includes these three families plus Hectorellaceae and Basellaceae.
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