Wood Anatomy of Begoniaceae, with Comments on Raylessness, Paedomorphosis, Relationships, Vessel Diameter, and Ecology

Abstract

CARLQUIST, S. (Rancho Santa Ana Botanic Garden and Department of Biology, Pomona College, Claremont, CA 9171 1). Wood anatomy of Begoniaceae, with comments on raylessness, paedomorphosis, relationships, vessel diameter, and ecology. Bull. Torrey Bot. Club 112: 59-69. 1985.-Six collections of four species of Begonia ranging from moderately to markedly woody (for the genus) are analyzed for qualitative and quantitative wood features. Begonia wood has vessels mostly solitary and oval or circular in outline, scalariform lateral wall pitting on vessels, tyloses in vessels, libriform fibers which are sometimes septate, vasicentric scanty axial parenchyma, tall and wide multiseriate rays (uniseriates absent) composed of erect cells (near-rayless in one collection), and storied structure. These features match those of Datiscaceae closely; features which do not may be related to the distinctive habit of woody Begoniaceae: semisucculent canelike stems of finite duration produced by a rhizome. As with similar stems of Piperaceae (which is not closely related to Begoniaceae), rays have erect cells predominantly or exclusively, rays alter little during ontogeny, and vessels have scalariform lateral wall pitting almost exclusively. These three features seem related to paedomorphosis, as does the presence of occasional scalariform perforation plates in early secondary xylem of Begonia. Quantitative features of Begonia wood mark all species as mesomorphic. Wood mesomorphy of B. parviflora increases with age of stem, suggesting greater transpiration from taller stems. Increase in vessel diameter with age is common in many dicotyledon trees and shrubs, and may relate to ability of progressively larger root systems to tap greater water supplies, as well as to the tendency for a larger and more exposed crown to transpire more. Some annual and short-lived perennial dicotyledons tend to have a progressive decrease in vessel diameter with age, which can be correlated with progressive drying of soil in the habitats of these species.