The Siluria1 - Many scientists now consider...

Info iconThis preview shows pages 1–2. Sign up to view the full content.

View Full Document Right Arrow Icon
The Silurian Plants divide into two large groups: vascular plants that contain lignified conducting cells, and the nonvascular plants, which do not. Some Silurian plant fossils might be algae or nonvascular plants. Vascular plants developed during the Silurian period, 400 million years ago. The earliest vascular plants had no roots, leaves, fruits, or flowers. Cooksonia is a typical early vascular plant. It was less than 15 cm tall, with stems that dichotomously branched. Dichotomous branching (where the stem divides into two ewqual branches) appears a primitive or ancestral trait in vascular plants. Some branches terminated in sporangia that produced a single size of spore.
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Background image of page 2
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: Many scientists now consider "Cooksonia" an evolutionary grade rather than a true monophyletic taxon. Their main argument is that not all stems of Cooksonia-type plants have vascular tissue. The evolutionary situation of a grade would have some members of the group having the trait, others not. The shapes of sporangia on various specimens of Cooksonia also vary considerably. Many of the early land plant fossils are not unequivocally those of vascular plants. The best such evidence is the presence of a trilete mark on spores produced by meiosis in a tetrahedral tetrad....
View Full Document

This note was uploaded on 11/29/2011 for the course BIO BSC1010 taught by Professor Gwenhauner during the Fall '10 term at Broward College.

Page1 / 2

The Siluria1 - Many scientists now consider...

This preview shows document pages 1 - 2. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online