Notes from a lecture by Dr K Allen.
Dr Allen began by describing the classes of plants which have evolved in geological time.
Angiosperms - flowering plants with seeds in cases. Developed in the Cretaceous.
Gymnosperms - coniferous plants with seeds not in cases. Developed in Upper Carboniferous.
Pteridophytes - Ferns with spores, needing water to reproduce. Carboniferous.
Bryophytes - Mosses and liverworts, with spores.
Thallophyta - algae and fungi with spores.
He then introduced us to the east coast of Greenland from the air, showing glaciers and pack ice even in summer, and bare mountain ridges of Devonian rocks. So much research goes on here every summer a seaplane for transport is justified.
Take Greenland back to Devonian times and due to plate tectonics it lay 40 degrees North or South of the Equator, not 60 degrees North as now. So tropical conditions prevailed, but it was a bare landscape, the plant world was not yet established. Also North America, Greenland, Britain and Scandinavia were joined together in a large land mass with high mountain ranges, a result of the Caledonian Orogeny. The main colour of the rocks was red, showing desert conditions with rivers draining from the mountains into inland lakes and swamps. These were times of flash floods, bringing down boulders and pebbles to form conglomerate delta fans, but in lenses fine grained muds and silts settled. Here the first land plants flourished. In the lakes the first fish developed and by the lakeside the first land plants grew.
By mid Devonian times in this environment, vegetation flourished and diversified. The means of reproduction was by spores, and from these, which vary considerably a classified plant flora has been ,ade. Spores make a very good index fossil for dating rocks. Some spores are found still attached to the sporeangia, indicating ythe site of growth, while other loose ones may have been blown in from other sites, e.g. upland plants would not be preserved.
In the Brecon Beacons of Lower Devonian age, remains of small club mosses, relations of those in Greenland, can be found.
Small amounts of fine grained blush rocks are collected from Greenland and taken back to the laboratory to be processed.
The spores can only be separated from the rock by boiling in hydrofloric, nitric and potassium chloride acids. The spores are then mounted on slides.
The first plants were found preserved in chert at Rhynie in Scotland, a vascular stem, some with a root System, others with none.
By mid Devonian times plants were larger and beginning to branch out and develop arborescence, the next step was to make wood and from there the magnificent fern trees of the Coal Measures developed.
Dr Allen finished with slides of the present day flora, all being very small, growing in crevices for shelter.