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Evolution of Angiosperms
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“The rapid development as far as
we can judge of all the higher
plants within recent geological
times is an abominable mystery.”
-- letter from C. Darwin to J. Hooker 2 July 1879
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Putative Angiosperm Ancestors
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Bennettiales?
Flowerlike, bisexual strobili
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Separate ovulate and pollen-bearing sporophylls
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Putative Angiosperm Ancestors
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Conflicting hypotheses
Remains an “abominable mystery”
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Unique characteristics of
Angiosperms
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Flowers
Seeds enclosed in carpel
Double fertilization  endosperm
Much reduced microgametophyte
Reduced megagametophyte (7 cells; 8 nuclei)
Stamens with paired pollen sacs
Sieve-tube elements & companion cells
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Earliest Angiosperm Fossils
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Pollen grains from 135 mya
Whole plant – Archaefructus
~ 125 mya
 Semi-aquatic
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Middle Cretaceous – many
lineages present
End Cretaceous – angiosperms
dominant
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Phylogenetic Relationships
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Monocots and Eudicots – 97% of angiosperms
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Monocots -- monophyletic
o
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Eudicots – monophyletic
o
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Synapomorphy – single cotyledon
Synapomorphy – triaperturate pollen
Remainder – multiple different evolutionary lines
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Some arose before monocot/dicot split
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Monoaperturate pollen
Magnoliids
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Major Angiosperm Groups
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Basal Angiosperms
Mesangiosperms
Magnoliids
 Monocots
 Basal Eudicots
 Eudicots
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o
o
Rosids
Asterids
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Groups of Angiosperms
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Basal Angiosperms
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ANITA grade
Amborella (shrub from New Caledonia)
 Nymphaeales (water lilies and some other aquatic
plants)
 Austrobaileyales (woody aromatic plants including
star anise).
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ANITA stands for the genera Amborella,
Nymphaea, Illicium, Trimenia and Austrobaileya.
Sister to all other angiosperms
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Amborella trichopoda
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Dioecious
Undifferentiated
stamens
Drupes
No vessels
Embryo sac – 8
celled and 9
nucleate
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The Rest of ANITA
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Nymphales – water lilies
Austrobaileya scandens
Plantsystematics.org
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Magnoliids
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Numerous, spirally arranged floral parts
Magnoliales (Magnolia), Laurales (Calycanthus),
Piperales (Piper and Aristolochia), Canellales
Many Australasian
Essential Oils – nutmeg, pepper & bay leaves
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Monocots
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Monoaperturate pollen
3-merous floral parts
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Eudicots
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Tricolpate pollen
4- and 5-merous floral parts
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Highly
Simplified
Angiosperm
Phylogeny
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Major Groups
of
Angiosperms
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Rosids
2 integuments
 Nucellus with 2 layers
of cells
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Asterids
Single ingegument
 Nucellus with 1 layer of
cells
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Earliest Angiosperms
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Flowers lacking a perianth
125 mya
Leefructus
Archarfructus
Resemble
Amborella
not Magnolia
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Evolution of the Flower
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Perianth – no distinct sepals and petals
Some petals derived from sepals
 Sepals derived from leaves
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Other petals apparently derives from stamens
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Sepals – same number vascular strands as leaves
Stamens – 1 vascular strand
Petals – 1 vascular strand
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Evolution of the Flower
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Stamens – diverse structure and function
Woody magnoliids – broad, colored and scented
 High degree of differentiation
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Evolution of the Flower
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Unspecialized carpels
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Extinct angiosperms – leaflike carpels
Most extant angiosperms – differentiated carpels
Variation in placentation
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Major Evolutionary Trends
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Different pollination vectors
Bisexual/ unisexual flowers
Differentiated perianth
Specialized pollinators develop
Fruit dispersal vectors
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Generalized Evolutionary Trends
1. Flowers with indefinite merosity  definite
merosity
2. Floral axis shortened; floral parts often fused
3. Ovary inferior; differentiated perianth
4. Actinomorphic symmetry  zygomorphic
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Floral Diversity
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Specialized Families
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Asteraceae and Orchidaceae – 2 largest families
Among the most specialized
One monocot – one eudicot
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Asteraceae
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Disk Flowers & Ray Flowers
Any combination thereof!
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Orchidaceae
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Highly specialized
flowers
Often intricate
pollinator relationships
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Pollinators
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Primative -- Wind
Indistinct & ineffective
 Flowers much reduced
 Copious amounts of pollen
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Animals Agents of Floral Evolution
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Plants can’t move around (DuH!) – depend on
“animals”
Co-evolution
 Perfect flowers – each visit more efficient!
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Beetle Pollinated
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Flowers open
Dull colored
Strong (usually) fruity odor
Floral parts thick
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Fly pollinated
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Carrion (or fruity) smell
Reddish to purple-brown
No nectar guides
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Bee pollinated
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Flowers open
Colored but not red
Sweet odor
Nectar guides
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Bee Pollination: milkweed leg trap
Pollen sacs [pollinium]
Butterfly Pollinated
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Flowers produce nectar
Various colors – reds
Sweet odor
Nectar guides
Often landing platforms
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Nocturnal Moth Pollination
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Open at night
Usually white (or light)
Strong/ sweet odor
Lots of nectar
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Deception Pollination
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False food reward
Sweet smell
 Nectar
 Mimic food-rewarding flowers
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Sexual deception
Pseudo-copulation
 Prominent in orchids
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Bat pollinated
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Flowers open at night
White
Strongly scented
Lots of pollen
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Bird Pollinated
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Copious, thin nectar
Little odor
Colorful – often red
Tubular
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Important Pigments
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Small number of pigments
Caretonoids
 Flavinoids -- Block UV
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Anthocyanins
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o
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Flavonols
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Water soluble
pH determines color
Colors can change post pollination
Colorless – white/ivory pigments
Betalains
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Only in Caryophyllids
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Marsh Marigold
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Outer yellow – UV absorbing carotenoids
Inner yellow – UV reflective flavinoid calchone
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Fruits
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Ripe ovary and associated structures
Fruit dispersal fundamental aspect of radiation
Parthenocarpic -- without fertilization and seed
development (e.g., banana, pineapple, citrus …)
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Fruit Types
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Simple Fruit
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Aggregate Fruit
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Individual carpels in a single flower
Multiple Fruit
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One of more fused carpels from single flower
Derived from an inflorescence (e.g., many flowers)
Accessory Fruit
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Tissue not from ovary
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Simple Fruits
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Fleshy or Dry at maturity
Fleshy
Berries – 1 –many seeds; all parts fleshy
 Drupes – 1 seeded; fleshy mesocarp; stony endocarp
 Pomes – compound inferior ovary – accessory fruit
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Dry
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Dehiscent – multiple seeds
o
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Legume, silique, follicle, capsule
Indehiscent – only one seed
o
Achene, samara, cypsels
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Fruit Dispersal
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Wind
Dandelions – cypselas
 Maples – schizocarp
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Water
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Coconut
Animals
Ingestion
 Adhering
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Self-dispersal
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Biochemical Evolution
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Secondary Metabolites
Alkaloids – morphine, cocaine, caffeine, nicotine
 Terpenoids – taxol, rubber, cardiac glycosides, isoprene
 Phenolics – flavonoids, tannins, lignins, catechols,
salicylic acid
 Quinones – coqnzyme Q
 Raphids – Calcium oxalate
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Secondary Metabolites
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Protect against herbivory
Reduce palatability
 Total avoidance
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Mustards – cabbage, horseradish, mustard
Avoided by most herbivorous insects
 Attractants for others (e.g., cabbage butterfly)
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Insects that do feed often brightly colored
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They are also protected from predation
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