XVI International Botanical Congess

Gnetum is a plant most similar to the angiosperms due to its leaf structure, reduction of gametophytes, number of seed lobes, traces of the past bisexuality. Only specialized xylem is an obstacle for its recognition as an ancestor of flowering plants. Primitive xylem of the first flowering plants was the cause of the search of their direct ancestors among the hypothetic seed ferns. It is more difficult to explain the detailed similarity of the evolutionary ways of Gnetum and flowering plants, than to make the primitiveness of the xylem of the first angiosperms clear. It can be explained by a hydrophilic despecialization. The features of seed covering themselves in all probability appeared as a way of ovule preservation against water. Probably the first flowering plants were represented by the direct ancestors of Nymphaeales.