The unilacunar two-trace nodal structure of the caudex of Rhodiola rosea L. (Grassulaceae)

The subterranean, monopodial caudex of Rhodiola rosea has unilacunar, two-trace nodes, whereas its annual leafy flowering shoots have the more common unilacunar, one-trace nodes. The double-traced unilacunar nodal structure of the highly specialized caudex is considered to be the advanced condition in this species as well as in the Crassulaceae in general. The character may be significant in evolutionary and systematics studies of the genus Rhodiola.