Gnetophyta: An Enigmatic Group of Seed Plants

3/4/98


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Table of Contents

Gnetophyta: An Enigmatic Group of Seed Plants

A Class of Only Three Orders and as Many Genera

Ephedra

Gnetum

Welwitschia mirabilis

Peculiarities of Welwitschia

Characteristics of Gnetophytes

Ephedra Megagametophyte

Features Shared with Angiosperms

Megasporogenesis

Microsporogenesis

Sterile Ovules

Ephedra Male Strobilus

Double Fertilization in Gnetophytes

Fertilization in Ephedra

Fertilization in Gnetum

Prerequisites for Double Fertilization

Common Ancestry or ...

Convergence?

The Cladograms

Fossil Gnetophyte Record - Triassic/Jurassic

Fossil Gnetophyte Record - Cretaceous

Food for Thought

Author: Thorsten Hebben