Vessels in Nelumbo (Nelumbonaceae)

Vessels have been previously reported in the roots (but not rhizomes) of Nelumbo on the basis of light microscopy. We have reinvestigated vessel occurrence in Nelumbo by means of scanning electron microscopy (SEM). On the basis of these studies, vessels are characteristic of root metaxylem. Pores in primary walls of pits of end walls of these vessels are various in size, but feature incomplete lysis of pit membranes, often with residual webs or threads of primary wall material, much as in vessels of primitive woody dicotyledons. In addition, we newly report occurrence of vessels in metaxylem of rhizomes; pores in these vessels are smaller and more confined than in those of roots. The present study offers not only data of possible use in determining the phylogenetic position of Nelumbonaceae, but also contributes evidence that vessel origin in Nelumbonaceae relates to habit and ecology. We conclude that organographic distribution of vessels in Nelumbo follows the patterns seen in monocotyledons, which, like Nymphaeaceae and other aquatics, have sympodial architecture.