Charles Darwin - The Origin of Species, published 24 Nov 1859, has had
a larger impact on Biology than any other work.
Taxonomists began to think of having their classification systems reflect
evolutionary relationships. This is sometimes very difficult as it may
conflict with the need for an easily referable classification.
Oldest angiosperm fossils are about 125 million years old
Angiosperm fossils are rare, it has been proposed that early angiosperms
evolved in the hills and uplands of the tropics where fossilization does
not occur. So, if this is true, we have no way of knowing what the earliest
angiosperms looked like. Once angiosperms moved into the lowlands, fossilization
occurred and we do have some records of these plants.
Angiosperms are clearly the most successful group of land plants. Why?
ADAPTIVE TRAITS IN EARLY ANGIOSPERMS
1. Tough leaves resistant to drought and cold.
2. Vessel members - efficient water-conducting cells
3. Tough, resistant seed coat
OTHER ADAPTIVE TRAITS OF ANGIOSPERMS
1. Precise systems of pollination and seed dispersal
2. Deciduous - enables plant to survive times when water is not available,
especially imporant in cold climates
3. Enormous chemical diversity provides protection
4. Evolution of herbaceous perennials and annuals. These can survive in
more severe habitats than woody plants.
Angiosperm evolution and the composition of floras are closely tied in with
continental movements. India is a good example. India was originally far
south, in a cool temperate climate, moved northward through the southern
arid zone, the tropics, and the southern arid zone. Most of India's original
plants and animals became extinct and were finally replaced by flora and
fauna from Eurasia.
EVOLUTION OF THE ANGIOSPERM FLOWER
Carpel is a folded leaf blade that has been modified in a variety
Stamens could have evolved from a leaflike structure; an alternative
is that they came from slender branch systems bearing terminal sporangia
Origin of sepals - probably derived directly from leaves
Origin of petals - possibly from leaves in some groups, probably derived
from stamens in most groups
GENERAL TRENDS IN FLORAL EVOLUTION
Evolutionary relationships among angiosperms is still actively debated.
The high levels of parallel and convergent evolution confound attempts
to construct evolutionary trees.