The Treatment of the Monocotyledons in an Evolutionary System of Classification

Abstract

The more characters to distinguish monocotyledons and dicotyledons that are taken into consideration, the more numerous become the families which exhibit both mono- and dicotyledonous characters. In particular, monocotyledons and ranalean dicotyledons appear intimately related and the gaps between them do not allow a distinction into classes to be made. The author, therefore, considers the monocotyledons and the ranalean dicotyledons as two extreme wings of a single natural unit, with the Annonaceae, Aristolochiaceae, Nymphaeaceae, and Piperaceae as connecting links. Within the monocotyledonous wing, 12 natural units of higher than ordinal level (superorders) may be tentatively recognized and arranged according to the number of dicotyledonous features they possess and to the degree of their systematic isolation. Whereas the groups which present at least a few clearly dicotyledonous characters (like Arales and Helobiae) occupy a more isolated position, the reduction or absence of dicotyledonous characters (as in the anemophilous monocotyledons) is accompanied by decreasing isolation. This indicates that among monocotyledons which have attained a high evolutionary level, convergence largely camouflages relationship.