[clarification needed] Mesangiospermae includes the following clades: Amborellales Nymphaeales Austrobaileyales magnoliids Chloranthales monocots Ceratophyllales eudicots The mesangiosperms are usually recognized in classification systems that do not assign groups to taxonomic rank.

It is defined as the most inclusive crown clade containing Platanus occidentalis, but not Amborella trichopoda, Nymphaea odorata, or Austrobaileya scandens.

[9] Molecular clock comparisons of DNA sequences indicate that the mesangiosperms originated between 140 and 150 Mya (million years ago) near the beginning of the Cretaceous period.

[11] By 135Mya, the mesangiosperms had radiated into 5 groups: Chloranthales, Magnoliids, Monocots, Ceratophyllales, and Eudicots.

In 2007, two studies attempted to resolve the phylogenetic relationships among these 5 groups by comparing large portions of their chloroplast genomes.

The approximately unbiased topology test showed that some of the other possible positions of the monocots had more than 5% probability of being correct.