Biology : The Time of Ancient Life : Part Nine
Life on Land:
The trimeophytes were large plants of the early-middle Devonian. Some trimerophytes are thought ancestral to the sphenopsids and progymnosperms of the later Devonian. Unlike the rhyniophytes, trimerophytes did not produce equal (dichotomous) branches. Instead they branched in such a way that one branch appeared to be the central stem and the other a side shoot.
Plants belonging to the division Lycophyta, have their sporangia organized into strobili (sing.: strobilus). Leaves contain vascular tissue.
Drepanophycus is a middle Devonian lycophyte from the Northern Hemisphere. Its features are very similar to modern lycophytes.
The major fossil groups of lycophytes are the lepidodendrids and sigillarids, often referred to as the arborescent lycopods because they usually were large trees. During the middle Devonian lycophytes retained their herbaceous habit, but also began to grow taller, more than a few meters high at first, and developed the capability for secondary growth to produce wood, allowing the plants to grow still taller. Modern lycophytes lack secondary growth and are entirely herbaceous.
Artist’s reconstruction of a Devonian forest. Lepidodendrid trees are on the right, sphenophytes on the left of the image.
© 2007 Aventa Learning. All rights reserved.