Les hydathodes des genres Begonia et Hillebrandia (Begoniaceae)

Abstract

The hydathodes of Hillebrandia sandwicensis and of Begonia augustinei, B. coccinea, B. phyllomaniaca, B. salicifolia, and B. vellozoana are described. Begoniaceae have typical epithem hydathodes. Indirect measures of ploidy level (number of chloroplasts per guard cell, stomatal size) indicate that aquiferous stomata could be endopolyploid relative to aeriferous ones. The epithem comprises nonmoruliform cells, and the intercellular spaces are small. Elongated epithemial cells are intermixed with tracheids, and the stomatal chamber is lined by isodiametric epithemial cells. Elongated parenchyma cells sheath the hydathode. The enlarged vein is excentric and asymmetrical, as has been described for the "begonioid" tooth; however, the tooth is not tylate (i.e., with a pad of dense cells which would correspond to the epithem), as its apex is composed of parenchymatous cells. The hydathodes of Begoniaceae species vary in size, in position of the aquiferous stomata, in size of the chamber, and by the presence or absence of tanniferous cells or macrosclereids. Hydathodes, as well as other anatomical characters from the margin, might prove useful in taxonomic and phylogenetic studies of the Begoniaceae.