Why are there so many angiosperms? Flashcards
How many species of angiosperms are there?
around 348,000 Wortley and Scotland 2004
Numbers are uncertain. estimates have ranged from 230,000-420,000
What percentage of embryophytes are angiosperms?
89.4%
Describe the world’s largest flower
Rafflesia flowers up to 1m in diameter.
Usually classified as Rafflesiaceae with uncertain phylogenetic affinities
Nested within Euphorbiaceae
73 fold increase in flower diameter
Name the world’s tallest flowering plants
Swamp gum/ mountain ash
Reaches over 100m and 17m girth in Tasmania and South Australia
List some of the habit and life history diversity
Trees, shrubs, herbs, ephemerals, annuals, biennials, perennials, bulbs, corms, rhizomes, switch plants, succulents, aquatics, climbers/lianas
every part of the plant and life cycle extensively modified in some angiosperm lineage. Habit, length and life cycle, underground storage organ, ecology
Angiosperm success relative to humans
They dominate man-made environments
The world is dependent on angiosperms for food, clothing, medicine, and energy
What are 4 main points of their success?
- Species numbers significant compared with other plant groups
- Morphologically diverse
- Ecologically diverse
- Co-exist in high-diversity assemblages relative to other plant groups
What are the possible explanations for their success?
Unique characters to flowering plants
Ecological opportunity
Extrinsic environmental factors
both of which Increase possibility of rate of speciation or reduce extinction
Biotic pollination - entomophily
Many angiosperms are insect pollinated (87% of animals)
Most gymnosperms wind pollinated
Entomophily has been argued to decrease extinction rates by maintaining gene flow in small, sparse populations and so ensuring their survival
Entomophily as a driver of speciation based on selection for pollinator specialisation e.g. orchids
How typical is anemophily for gymnosperms?
Angiosperms arose after the origin of entomophily in one or more gymnosperms
The most important group of insect pollinators, the Hymnenoptera, first appear in early Triassic
Many cycads (gymnosperm) are obligate entomophiles, but cycads are not an especially species rich group.
Gnetalian (gymnosperm) species at least show a degree of adaptation to entomophily
Evidence of beetle pollination in Bennettitales (fossil gymnosperms)
Comments on entomophilu
Absence of empirical evidence for greater inter-populational gene flow in entomophilous taxa
Wind pollination has evolved repeatedly from insect pollinated ancestors giving rise to several evolutionarily successful angiosperm groups e.g. Graminoid monocots (grasses, sedges, and rushes) and Fagaceae
Early entomophilous plant generalists and specialised plant-pollinator relationship appeared relatively late with angiosperm
Maybe…. specialised entomophily rather than entomophily per se is the angiosperm innovation
More efficient water transport - maybe?
Increased efficiency of water uptake and thus growth rates , particularly among seedlings
Tundra where gymnosperm predominate, soils are frozen so better water uptake is not an issue, but in other habitats, where other angiosperms predominate, it is
Most but not all angiosperms have vessels
Gnetales have vessels - homologous?
Many early angiosperms have tracheids
What is the carpel and what did carpel evolution lead to?
An unambiguous synapomorphy
Pollen tube competition
Incompatibility systems
Many fruit types
How might faster life history have been a factor?
Paedomorphic trends within angiosperms relative to gymnosperms
Paedomorphosis: precocious reproductive maturation
Faster life cycles e.g. Arabidopsis
Gymnosperms are exclusively woody, no herbs or annuals
Not a synapomorphy e.g. many basal angiosperms are woody
Describe South African semi desert ice plants
Succulent Karoo is an arid region of Cape
Onset of recent aridity c5 mya
Adjacent areas experiencing aridity on and off since the Cretaceous
5000 species - 40% endemism
