Australia: The Land Where Time Began

A biography of the Australian continent 

Rhynia, Ancestral to Ferns, Horsetails and Seed-plants

This vascular plant occurs in the Rhynie Flora in a deposit of chert (a silica rick) at Rhynie in Aberdeenshire, Scotland. At this site the plants grew in a marshy area near a volcano. When boiling silica-rich water from volcanic eruptions flowed over the marsh all the plants were killed instantly and the silica permeated their tissues, the silica replacing all plants material with silica molecules so that the plants were preserved in a perfect, lithified state, the finest detail of their internal structure being retained.

The Rhynie plants consisted of small erect branches that rose from a network of prostrate branches that carried out the function of roots, gathering water and nutrients that were passed up the erect branches. They were probably aided by Mycorrhizal Fungi as plant roots are at the present. Their surface was covered with a cuticle and they had stomata, as do modern plants, and terminal sporangia. All green cells, wherever on the plant, carried out photosynthesis. The stems had a vascular core, including tracheids (elongated cells in the xylem that specialised in transporting water from the roots), and on the outside of xylem, phloem that conducted the sugar produced by photosynthesis to all parts of the plant, as well as other substances such as plant hormones.

The sporophyte bears the terminal sporangia. The gametophyte generation are on similar stems, with sperm and egg cells in small cup-like structures in the surface tissue. It has been suggested that the sporophyte had erect stems to raise the spores above the ground to increase the dispersal by the wind, while the gametophyte may have had prostate stems.

On the Rhynia line, leaves are believed to have evolved by modifying small lateral branches produced by unequal division of cells in the stem. Then flattening of the branches to increase the photosynthetic area, followed by the addition of tissue between the branches to form the lamina of the leaf.

Sources & Further reading

  1. White, Mary E., 1994, The Greening of Gondwana, the 400 Million Year story of Australian Plants, Reed.
Author: M. H. Monroe
Last updated  30/11/2011
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