Alternation of generations
in mosses and ferns
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
1. Adaptation to living on land and
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/~flemin00/pteridology/pteridology.html
Horsetails: Equisetum
Equisetum arvense
The ‘scouring rush’
Vegetative and
reproductive axis bearing
sporangia
http://www.ansci.cornell.edu/cgi-bin/db2www/plant_indiv.d2w/PHOTO?keynum=36
2. History of evolution of major plant types
History of plant groups
Fig. 17.3A
3. Alternation of generations
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. 17.3A
5. Fern life cycle
Fern life cycle
Fig 17.6
http://departments.bloomu.edu/biology/chamuris/concepts2/labimg.html
Sporangia
Polypodium spp
sori
sporangia
A sorus
Polypodium spp
a
g
n
i
f
i
e
d
Sporangia
Developing spores
Polypodium spp
Gametophyte
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/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