1. Adaptation to living on land and the first land plants

2. History of evolution of major plant types

3. Alternation of generations

4. Moss life cycle

5. Fern life cycle

Alternation of generations in mosses and ferns

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

1. Adaptation to living on land and the first land plants

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.

Advantages of being small

Devonian

plant community

Devonian plant community found at Rhynie, in Scotland. A reed-like marsh, 370-380 million years ago.

Simple dichotomous branching

MAIN FEATURES

!5 to 30 cm tall

No roots

Stomata with guard cells

Most had a central vascular strand

Cuticle

Asteroxylon had leaves –without a vascular connection

Sporangia

Asteroxylon

Lycopodium

Lycopodium, club mosses, share many features with Asteroxylon, but they do have roots.

http://web.utk.edu/~flemin00/pteridology/pteridology.html

http://www.ansci.cornell.edu/cgi-bin/db2www/plant_indiv.d2w/PHOTO?keynum=36

Equisetum arvense

Horsetails: Equisetum

Vegetative and reproductive axis bearing sporangia

The ‘scouring rush’

History of plant groups

2. History of evolution of major plant types

Fig. 17.3A

Alternation of generations

Fig. 17.4

3. Alternation of generations

Fig. 17.5

4. Moss life cycle

Moss sporophyte

Top of capsule

Developing protonema

Moss antheridium and archegonium

Fig. 17.3A

Fern life cycle

Fig 17.6

5. Fern life cycle

Sporangia Polypodium spp

sori

sporangia

http://departments.bloomu.edu/biology/chamuris/concepts2/labimg.html

A sorus

Magnified sporangia

Polypodium spp

Sporangia

Developing spores

Gametophyte

Polypodium spp

Gametophyte

Developing sporophyte

Arrangement of sporangia on two ferns

In lines on a broadleaved type At the end of the leavesAdiantumAsplenium

Cibotium menziesii in habitat in Hawaii.  Photo courtesy of Peter Richardson.

Cyathea australis with the uncurling croziers visible.  Photo courtesy of Scott Ridges

Tree ferns

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).

Coal formation

Anaerobic conditions and periodic inundations of the sea

Early Carboniferous

Britain

Ice cap

EquatorAppalachians

Late Carboniferous

Britain

Ice cap

EquatorAppalachians

Fossil

Lepidophylloides

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/Lepidophylloides1.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