This document summarizes key trends in plant evolution such as the reduction of the gametophyte generation and specialization of the sporophyte generation. It also describes the development of vascular tissue which improved water and nutrient transport within plants. Additionally, it reviews plant classification including bryophytes, seedless vascular plants like ferns and horsetails, gymnosperms, and flowering plants. Seedless vascular plants were dominant during the late Devonian through early Permian time periods but today are more marginal in their success.
Plant Evolution Trends in Vascular Tissue and Specialization
1. Continuing Trends in PlantContinuing Trends in Plant
EvolutionEvolution
• Reduction of water-dependent gametophyte
• Vascular tissue – improved water/food
transport
• More efficient roots, stems, leaves
* Tissues
* Stomates
Green: all these are in sporophyte
6. Seedless Vascular PlantsSeedless Vascular Plants
• Ferns, horsetails, club mosses, whisk ferns
• Sporophyte dominant
• Gametophyte small but still tied to water
• Dominant plants from late Devonian
through early Permian
* Equatorial coal forests
• Today somewhat marginal, but successful
• Heterospory in some (next time)
7.
8. Fern Life CycleFern Life Cycle
Gametophyte
Fertilizatio
n
Sporophyte
M
eiosis
9. Fern gametophytes …
… with young sporophytes
Mature fern sporophyte …
… with clusters of sporangia
You do not need to know the details of this life cycle. Just, Where is the gametophyte and sporophyte?
Psilotum is subtropical
Exhibits several very primitive characters
No leaves (outgrowths of stem are not vascularized)
Dichotomous (equal “Y” shaped) branching of parts
Simple sporangia (in 3s)
“Roots” and stems similar morphology and vascular tissue simple
Lycophyta – Club mosses
Sphenophyta – Horse tails
Not seen: Tree ferns (Pterophyta) and seed ferns
Many giant, tree-sized versions of modern genera