Systematic root anatomy of Asparagales and other monocotyledons

Root anatomy of several taxa of Asparagales and some taxa formerly included in Asparagales is described in a systematic context together with a litera ture review. The presence of a dimorphic outer layer with long and short ce lls is widespread in monocotyledons, indicating that it originated early il l the monocot lineage, but whereas this layer is rhizodermal in most monoco tyledons, in Asparagales and Araceae it is usually hypodermal. There may be a correlation between the presence of a velamen or a persistent rhizodermi s in many Asparagales and Araceae and the presence of a dimorphic hypoderma l layer. Many other root anatomical characters, such as the presence of vas cular bundles in the central pith and a multi-layered sclereachymatous cyli nder, are probably xeromorphic and developed convergently.