The gymnosperms include conifers, cycads, gnetales and ginkgos and these may have appeared as a result of a whole genome duplication event which took place about 319 million years ago.
12.
They are thought to have pollinated such plants as Caytoniaceae, Cheirolepidiaceae, Czekanowskiaceae, Pentoxylaceae, and Gnetales, as their ovulate organs are either poorly suited for wind pollination or have structures that could support long-proboscid fluid feeding.
13.
Some more recent studies have used the word anthophyte to describe a group which includes the angiosperms and a variety of fossils ( glossopterids, " Pentoxylon ", Bennettitales, and " Caytonia " ), but not the Gnetales.
14.
It was once thought that vessel elements were an evolutionary innovation of flowering plants, but their absence from some basal angiosperms and their presence in some members of the Gnetales suggest that this hypothesis must be re-examined; vessel elements in Gnetales may not be homologous with those of angiosperms, or vessel elements that originated in a precursor to the angiosperms may have been subsequently lost in some basal lineages ( e . g ., Amborellaceae, Tetracentraceae, Trochodendraceae, and Winteraceae ), described by Arthur Cronquist as " primitively vesselless ".
15.
It was once thought that vessel elements were an evolutionary innovation of flowering plants, but their absence from some basal angiosperms and their presence in some members of the Gnetales suggest that this hypothesis must be re-examined; vessel elements in Gnetales may not be homologous with those of angiosperms, or vessel elements that originated in a precursor to the angiosperms may have been subsequently lost in some basal lineages ( e . g ., Amborellaceae, Tetracentraceae, Trochodendraceae, and Winteraceae ), described by Arthur Cronquist as " primitively vesselless ".
