Available at http://planet.uwc.ac.za/nisl/Eco_people/Presentations/

Angiosperms-the flowering plants have arrived

Simone Neethling

Biodiversity and Conservation Biology Department

University of the Western Cape

Introduction Angiosperms are flowering plants that

cover their seeds in a true fruit. Their reproductive organs; an

androecium (male) and/or gynoecium (female) lies within the flower structure.

Primitive angiosperms are dioecious whereas modern angiosperms are monoecious.

Angiosperms are highly successful and dominate the vegetation of the earth’s surface.

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Classification

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Morphology and anatomy The androecium consists of stamens, made up of anthers and

filaments. The gynoecium consists of the pistil, made up of the style and

stigma. Pollen grains germinate on the stigma, grains have numerous

sutures through which a germination tube can emerge thereby ensuring that grains will not land upside down and result in unfavourable germination conditions.

The perianth, also forming part of the reproductive system, consists of units that may be differentiated into petals and sepals.

There are two other organ systems in angiosperms as well as other plants, namely an anchorage and production system.

Morphology and anatomy

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Morphology and anatomy

Angiosperms are also anatomically complex organisms.

Dicots have vascular tissues within their stems, roots and leaves that is made up of xylem and phloem bundles in a fixed arrangement this arrangement distinguishes dicots from monocots as monocots’ bundles are scattered.

Dicots’ vascular bundles consist of secondary xylem and phloem produced by the cambium within.

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Origin The Cretaceous era (145-65 million

years ago) saw the rise of flowering plants and their associated insect pollinators through the process of co-evolution.

This process between plants and insects was most probably the most influential driving force behind the origin and diversification of angiosperms, although it has been disputed that flexibility in seed production, dispersal and seeding establishment was the most important factors in angiosperm origin.

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Origin Two basic hypotheses:Magnolialean and Herbaceous origin

hypothesis. The Magnolialean hypothesis suggests that the first angiosperms on

earth were woody with large, many parted flowers. These flowering plants were shrubs of semi-xerophytic origin that

entered mesic areas as colonizers of unstable habitats – “the weeds of the Early Cretaceous” based on fossil evidence.

These Magnolia – like ancestral angiosperms were distinguished from cycad-like gymnosperms, from which they evolved, by having a closed carpel, smaller leaves and sculptured pollen grains and loved in disturbed habitats like stream margins and gravel bars with coarse grained sediments.

Herbaceous origin hypothesis implies that the first Angiosperms were small in size and had smaller, few parted flowers. This hypothesis suggests that Angiosperms are derived from a compound gymnosperm; similar to gnetopsids

Impact on other eco-systems

Angiosperms had major impacts on the evolution of other types of plants and animals.

The increase in angiosperms was paralleled by the decline of ferns.

Another major driving force behind the rise of angiosperms and angiosperm fruit is the co-evolution feedback between plants and vertebrates that dispersed the fruit.

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Angiosperm adaptations to pollination Pollination is a process where pollen is transported from the anther

to the stigma. Flowers have adapted in order to attract pollinators. Adaptations

include visual cues whereby colour patterns that resemble a “bull’s eye” are utilized.

Pollinators therefore see the flower as the target and can be differentiated from the background green foliage.

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Angiosperm adaptations to pollination Flowering plants have also adapted olfactory cues as some

pollinators use their olfactory sense much more than their visual sense; some flowers are also not as visually stimulating as others therefore flowers have also evolved scents.

During the process of pollination, pollinators need to benefit from the transportation of pollen therefore rewards for the pollinator has to be present. Flowers therefore produce nectar a valuable food resource.

Flowers also produce extra pollen as some pollinators feed on pollen e.g. bees.

http://www.botanical-online.com/floresadaptacionesangles.htm

Angiosperm adaptations to pollination

The shape of the flower plays a major role for example corollas of some Erica’s are strongly curved to match the beak shape of the main pollinator, the Orange-breasted Sunbird found in South Africa.

In fly-pollinated Erica’s, the mouth of corolla is much smaller and lobes are large, star-shaped and spreading thereby providing a landing pad for flies as they insert their long proboscis into the flower to drink nectar.

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References Corbet SA (1978) Bees and the nectar of Echium vulgare. Linnean

Society Symposium Series 6:21-30

 Mader SS (2004) Biology 8th Edition. McGraw-Hill, New York, pp 428. ISBN 0-07-241882-6

Pearson LC (1995) The Diversity and Evolution of Plants. CRC Press, Inc., United States of America, pp 524-529. ISBN 0-8493-2483-1

Taylor DW and Hickey LJ (1996) Flowering Plant Origin, Evolution and Phylogeny. Chapman and Hall, New York, PP176-178. ISBN 0-412-05341- 

References Angiosperms

http://en.wikipedia.org/wiki/Angiosperms#HistoryAccessed:13/03/2006 

Angiospermshttp://www.geocites.com/we_evolve/plants/angiosperms.html Accessed:13/03/2006 

Pollination Adaptationshttp://plantphys.info/Plants_Human/pollen.adapt.htmlAccessed:28/03/2005 

Flowershttp://www.botanical-online.com/floresadaptacionesangles.htmAccessed:28/03/2005

http://www.unifiedworld.comAccessed:28/03/2005