Wood Anatomy of Portulacaceae and Hectorellaceae: Ecological, Habital, and Systematic Implications
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چکیده
A B STR ACT 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). Most Portulacaceae show modifications that can be related to the succulent habit, including wide, tall rays mostly composed of thin-wall ed cells; tota l or partial substitution of axial parenchyma for libriform fibers ; and modified patterns of pitting on lateral wa ll s of vessels. Pseudo-scalariform pitting is more common in Portulacaceae than in other dicotyledon families. 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 Portulacaceae as a whole are markedly xeromorphic with respect to vesse l e le me nt dimensions, vessel density, and vessel grouping; wood of Lewisia and Hectorella is especi all y xeromorphic. Xeromorphism is not so pronounced in succulent dicotyledons at large. 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 Hec-torellaceae and Basellaceae. The wood of Heclorella is very s imilar to that of Lewisia rediviva and contains no features not also observed in Portulacaceae. Tracheidlike idioblasts in rays of Anacamp-seros 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 likel y to be a homoplasy; they occur in a scattering of Caryophyllales.
منابع مشابه
Molecular Evidence Resolving the Systematic Position of Hectorella (Portulacaceae)
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تاریخ انتشار 2016