J Syst Evol ›› 2005, Vol. 43 ›› Issue (5): 420-430.

• Research Articles •

### Consideration on some viewpoints in researches of the origin of angiosperms

LU An‐Ming, TANG Yan‐Cheng

1. (Laboratory of Systematic and Evolutionary Botany, Institute of Botany, the Chinese Academy of Sciences, Beijing 100093, China)
• Published:2005-09-18

Abstract: In this paper, some viewpoints on the origin of angiosperms are discussed. (1) The angiosperms share certain remarkably consistent character syndrome, and thus it is unlikely that they evolved from more than one ancestor, although they might have a common ancestor group. The angiosperms should be a group of unitary origin. The classification systems of extant angiosperms were constructed based on comprehensive evidence from morphological, molecular systematics, palaeobotanical, and phytogeographical studies, and could only express affinity among the extant angiosperms. At present it is impossible to construct a phylogenetic system that contains all extinct and extant angiosperm groups, and for this reason the classification systems of extant angiosperms can only be considered as “affinity” ones. (2) The evidence from molecular clocks, fossils and geographic distribution data on the origin time of angiosperms has been greatly accumulated in the past two decades. Fossil data are very important for determination of the origin time of angiosperms. However, fossil evidence is only the integrated embodiment for the preserved parts of plants and geological fossilization conditions, but is not, and unlikely to be, the indicator of the exact age of the groups or species. In addition, we have to consider the evolutionary history of the fossils. The application of molecular clocks is another approach, but it carries even greater errors. Besides the two lines of evidence, researches on modern distribution patterns, the formation of the plant groups, and combination of plant evolution with the earth history as well as the theory of plate tectonics, can undoubtedly improve the reliability in inferring angiosperm origin time. Analyses of 56 important spermatophyte (mostly angiosperms) families or genera at different evolutionary levels have suggested that the origin time of angiosperms could be dated back to the Early Jurassic or Late Triassic. (3) The nature of basal angiosperm groups, i.e., members of ANITA grade (incl. Amborellaceae, Nymphaeaceae, Illiciales, Trimeniaceae and Austrobaileyaceae), is analyzed. Views on the systematic positions of ANITA members in modern classification systems of angiosperms are discussed, and their morphological characters (sensu lato) are evaluated. We consider that the ANITA members belong to the primitive groups because of their many plesiomorphies. But they only share few synapomorphies, such as globose pollen grains, indicating that they may have already diverged into different lineages during the early stages of angiosperm evolution. Therefore, ANITA is a complex group originated from different lineages.