Developmental Patterns in Stem Primary Xylem of Woody Ranales. I. Species With Unilacunar Nodes

Patterns of protoxylem strands in vegetative stems of 11 species representing eight families of woody Ranales are illustrated and discussed. Primary vascular systems of many species examined tend to be pseudosiphonostelic. Protoxylem tissue, however, is discontinuous and consists of discrete strands which develop basipetally. The author assumes that data pertaining to the morphology of these protoxylem strand patterns can be significant in determining phylogenetic relationships among ranalean families and between these and higher angiosperms. The value of the primary vascular system in past taxonomic investigations is also considered. Results of this study indicate that the protoxylem strand patterns of 11 woody ranalean species are diverse even though the species are characterized by identical phyllotaxis and nodal structure.