Based on the chloroplast matK gene sequence, a phylogenetic analysis of the
Urticales in its traditional circumscription and its putative affinities p
roduced three equally most parsimonious trees with tree length = 1527 steps
, CI = 0.6863 and RI = 0.6352, indicating that the Ulmaceae s. l. are polyp
hyletic while the Celtidaceae are paraphyletic, and particularly, Cannabis
and Humulus in the Cannabaceae are consistently nested within the Celtidace
ae. Therefore, the present data strongly suggest that the Cannabaceae shoul
d be merged with the Celtidaceae to form a monophyletic group. According to
the present study, the Celtidaceae including Cannabaceae are more closely
related to the Moraceae and Urticaceae than to the Ulmaceae s. str.. Gironn
iera and Aphananthe are both basal clades of the Celtidaceae rather than me
mbers of Ulmaceae s. str.. The Rhamnaceae and Rosaceae are the closest rela
tives of the traditional Urticales, which is very congruent with the newest
system of flowering plants put forward by APG.