Alternation of generations in mosses and ferns 1

Alternation of generations in mosses and ferns 1. Adaptation to living on land the first land plants 2. History of evolution of major plant types 3. Alternation of generations 4. Moss life cycle 5. Fern life cycle

1. Adaptation to living on land the first land plants The land that land plants colonized was hostile to life. Soil development was minimal. Land plants grow in an environment that does not support them. They require several adaptations to be successful: mechanical strength for support, exposed light catching surfaces, anchoring system, conducting system for water, system for obtaining mineral nutrients, a way to restrict water loss in desiccating air, a means of reproducing and dispersing on land

Advantages of being small An advantage of being small is that many of the requirements for living on land are minimized. Close to the soil surface the environment can be almost aquatic – even if it does not rain continuously. Then the principal adaptation required becomes the ability to withstand the dry periods between the wet.

Devonian plant community found at Rhynie, in Scotland. A reed-like marsh, 370 -380 million years ago. Asteroxylon MAIN FEATURES Simple dichotomous branching Sporangia !5 to 30 cm tall No roots Stomata with guard cells Most had a central vascular strand Cuticle Devonian plant community Asteroxylon had leaves – without a vascular connection

Lycopodium, club mosses, share many features with Asteroxylon, but they do have roots. Lycopodium http: //web. utk. edu/~flemin 00/pteridology. html

Horsetails: Equisetum arvense The ‘scouring rush’ Vegetative and reproductive axis bearing sporangia http: //www. ansci. cornell. edu/cgi-bin/db 2 www/plant_indiv. d 2 w/PHOTO? keynum=36

2. History of evolution of major plant types History of plant groups Fig. 17. 3 A

3. Alternation of generations Fig. 17. 4

4. Moss life cycle Fig. 17. 5

Moss sporophyte Top of capsule

Developing protonema

Moss antheridium and archegonium

Fig. 17. 3 A

5. Fern life cycle Fig 17. 6

http: //departments. bloomu. edu/biology/chamuris/concepts 2/labimg. html Sporangia Polypodium spp sori sporangia A sorus

Polypodium spp Sporangia Developing spores

Polypodium spp Gametophyte Developing sporophyte

Arrangement of sporangia on two ferns In lines on a broadleaved type Asplenium At the end of the leaves Adiantum

Tree ferns Cibotium menziesii in habitat in Hawaii. Photo courtesy of Peter Richardson. Cyathea australis with the uncurling croziers visible. Photo courtesy of Scott Ridges

Coal formation Jungle-like forests of the Carboniferous were dominated by giant ancestors of club mosses, horsetails, ferns, conifers, and cycads. Most of the plant fossils found in the coals and associated sedimentary rocks show no annual growth rings, suggesting rapid growth rates and lack of seasonal variation in the climate (tropical). Anaerobic conditions and periodic inundations of the sea

Early Carboniferous Equator Appalachians Britain Ice cap

Late Carboniferous Equator Appalachians Britain Ice cap

Lepidophylloides Fossil Lepidophylloides is the name assigned to the leaves of the Lepidodendron tree. Rock Type: Gray shale Age: Middle Pennsylvanian Period, approx. 312 million years. http: //www. clearlight. com/~mhieb/WVFossils/Lepidophylloides 1. html

Sections you need to have read 17. 1 17. 2 17. 3 17. 4 17. 5 17. 6 17. 7 Courses that deal with this topic Botany 113 Plant Identification and Classification Botany 350 Introduction to Plant Geography Geology 203 Evolution of the Earth