Are the Angiosperms Primitively Vesselless?

The hypothesis that angiosperms are primitively vesselless was tested in the context of a cladistic analysis of selected families of the Magnoliidae, Ra- nunculidae, and Hamamelididae. Results of this analysis show that the most parsi- monious explanation of the absence of vessels in dicotyledons is that in all instances it is a derived feature. This conclusion is supported by three taxon out-group com- parisons and does not alter our well-founded understanding of vessel member evo- lution within the angiosperms. I suggest that presence of vessel members with sca- lariform perforation plates and scalariform intervascular pitting, such as those in Austrobaileya, is the condition within the angiosperms. I also suggest that in the earliest angiosperms vessels were restricted to secondary xylem. Absence of vessels in the eleven extant genera of woody dicotyledons is a secondary loss, and it is suggested that the xylem of these genera is paedomorphic. Perhaps one of the most widely accepted hypotheses regarding the evolution of angiosperms is that they are primitively vesselless (Bailey 1957a). That is, absence of vessels in the xylem of taxa of the woody, dicotyledonous families Winteraceae, Chloranthaceae, Amborellaceae, Trochodendraceae, and Tetracentraceae (table 1), and perhaps the her- baceous Nymphaeales, represents retention of a primitive feature.