STRUCTURE AND FUNCTION OF TRACHEARY ELEMENTS IN AMBORELLA TRICHOPODA

Recent phylogenetic analyses have placed the root of flowering plants near Amborella trichopoda, a woody plant restricted to cloud forest habitats in New Caledonia. A distinctive feature of A. trichopoda is its reported lack of xylem vessels. Here we present observations of pit membrane structure and end wall morphology for primary and secondary tracheary cells of A. trichopoda as well as field measurements of stem hydraulic properties of A. trichopoda compared with five cloud fforest species from New Caledonia. Observations of stem radial sections revealed that the primary wall material in the protoxylem and metaxylem elements was intact. No large porosities (such as those that have been observed in the pit membranes of Nymphaeales) were observed. However, a few elliptical pits of tracheary cells in the secondary xylem appeared to lack pit membranes. These observations are consistent with our measurements of functional conduit length, which indicate that the longest open conduits are equal to the length ...