[Molecular biological research on the origin of the angiosperms]

Nucleotide sequence of 23S-5S chloroplast rDNA spacer region including 4.5S rRNA gene of several dozens of seed plants was determined. The data obtained were used to construct phylogenetic trees and to compare them with the analogous data from literature. Topologies of trees constructed for various types of macromolecules and by different methods demonstrate obvious similarities although they are not identical. Some clue stages of seed plants evolution still remain obscure. Critical analysis of all the available information allows to come to several more or less definite conclusions. All the data say that angiosperms are a monophyletic group which diversified far before their fossils are definitely registered, i.e., before lower Cretaceous. Ancestral angiosperms were not genealogicaly related to modern woody Magnoliales but were represented by "paleoherbs", i. e. herbaceous and semiherbaceous magnoliids and monocots. Monocots originated at the earliest stages of angiosperms evolution and are not, probably, monophyletic. Woody Magnoliales and eudicots with tricolpate pollen seem to appear later in evolution. The conclusion that Gnetales is a sister group to angiosperms does not find enough support in molecular studies. Summing up, it looks as if a long period of existence of angiophytes preceded the pre-Cretaceous angiosperms irradiation. This line of development originated simultaneously with phylogenetic lineages of modern gymnosperms.