October 28, 2004. Copyright 2004, Graphic News. All rights reserved

A Seed in Time: New Insights into the Evolution of Modern Plants
By Mark Rutter

LONDON, October 28, Graphic News:  Scientists believe they have observed the earliest known plant seeds. The discovery of these prehistoric ancestors of modern day vegetation has shed new light onto how flowering plants and conifers came into existence. Modern seed-forming plants are descended from primitive flora such as algae, moss and ferns, ancient life forms which reproduce by forming simple structures known as spores. Since spores cannot tolerate dry conditions, such ancient plant life is largely confined to water or damp places. 

The success of modern plants owes much to the ability to form highly robust seeds that are much more complex than spores. They contain an embryo plant and food supply within a tough wall, and are better able to resist the ravages of sunlight, temperature extremes and drying. As a result, around 250,000 different species of seed-forming plants can now be found around the globe, in habitats ranging from cold arctic regions to the driest deserts.

Despite their importance in plant evolution, there are many conflicting views on how primitive plants developed the ability to produce seeds. The new study published in the journal Science (October 29, 2004) used fossils of Runcaria to try to increase our understanding of this process. Although these early plants show some differences in the arrangement and structure of the seed forming apparatus, several important similarities point to Runcaria being a close relative of modern seed-producing plants. 

The scientists that carried out the investigation believe that Runcaria reproduced by forming primitive seeds on a cup-like structure or cupule. The seed-like structures, which are 6.5mm to 8mm in length, have an enlarged pollen-trapping tip extending into the air. This suggests that these early seed-like plants, like many modern seed-forming plants, relied on the wind for pollination.

Other recent studies using DNA analysis have calculated that seed-forming plants first appeared on earth 341-360 million years ago. By looking at fossil records, this latest study has estimated the time at which the first seeds evolved to be much earlier at between 385 and 365 million years ago. It has also provided useful information on the make-up of primitive seeds and the arrangement of the structures on which they are formed.
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