What did the first angiosperms look like

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What did the first angiosperms look like?

• For many decades one of the big questions was
  whether the original angiosperms where trees
  shrubs or small herbs?
• Each has implications for our understanding of
• angiosperm origins
• What the 1st angiosperms looked like

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• Unfortunately, cladistic analysis of morphology
  has given two different results

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Woody Magnoliid Hypothesis

• Proposed by Arber Parkin (1907), expanded on
  by Takhtajan Cronquist, supported by cladistics
  of Doyle Donoghue

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Woody Magnoliids basal
Cladogram by Doyle
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• Magnoliales, Laurales Winterales seen as
  basal living fossils
• 1st angiosperms lived in tropical forests as
  evergreen understory trees shrubs
• Flowers large, bisexual, with many free
  spirally arranged parts
• Laminar (undifferentiated) stamens
• Carpel conduplicate (not full fused)

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Evolutionary trends in stamens
Primitive
Evolutionary trends in carpels
Primitive
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Most of the pictures of plants flowers in this
slide presentation are taken from one of your
recommended text books JUDD, WS., CAMPBELL, CS,
KELLOGG, EA, STEVENS, PF DONOGHUE, MJ. 2008.
Plant Systematics A Phylogenetic Approach.
Sinauer Associates, Sunderland Please consult it
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• Takhtajan saw the Winteraceae as the most
  primitive living angiopserm
• Has medium sized flowers wood without vessels

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• Fits nicely with
• -- Euanthial flower theory
• -- Evolution from Glossopterid-line of
  gymnosperms (Glossopteris or Gigantopteris)
• Stebbins semiarid origin, Axelrods upland
  origins Retallack Dilchers coastal origin
  are different angles on this hypothesis

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Paleoherb Hypothesis

• Supported by cladistics of Taylor Hickey

Paleoherbs
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• Chloranthaceae, Piperales Nymphaeales seen as
  basal living fossils
• 1st angiosperms lived in tropical forests as
  understory herbs
• Flowers small with few radially arranged parts
• Carpel generally fused

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• Fits nicely with
• -- Pseudanthial flower theory
• -- Evolution from Pine-line of gymnosperms
  (Cordiates or Gnetales)
• Taylor Hickey proposed that these herbs
  originated in annually disturbed riversides

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• But what do the latest morphological
  molecular cladograms tell us?

Saarela et al., 2007 Cladogram constructed from
both molecules morphology
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• Best we can do is analyse the grades of plants
  at the base of the cladogram to see what they
  have in common
• Common characteristics may have been inherited
  from a common ancestor so tell us something
  about the structure of this ancestor.

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Basal Angiosperm Grades
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Waterlily clade
Amborella clade
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Austrobaileyales
Austrobaileya
Trimenia
Schisandra
Illicium
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• WARNING
• 1. Basal angiosperms may not be representative of
  the earliest angiosperms, which actually may be
  extinct.
• 2. They may not even represent the earliest
  angiosperm diversification

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• Taking Amborella as the archetypical primitive
  angiosperm, and deeply seated morphological
  trends found within the basal angiosperm grade we
  can make the following inferences about what the
  1st angiosperms may have looked like
• These ancient angiosperms may have looked
  something like this
• 1. Weakly woody stems (possibly even semi-woody
  lianas??)

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Amborellales Woody shrub
Nymphaeales Aquatic Herbs
Austrobaileyales Woody (some lianas)
? Does not solves the problem. Cannot say for
certain if 1st angiosperms were woody or
herbaceous
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• 2. Good ability to undergo vegetative
  reproduction by resprouting
• 3. Simple leaves with pinnately reticulate
  venation
• 4. Medium to small sized flowers in cymose
  inflorescences
• Flowers unisexual (rarely bisexual)

Amborella
?
?
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• Flowers with spirally arranged parts
• Flowers with medium number of unfused parts
• Perianth bract-like undifferentiated, if
  differentiated then weakly so
• Petal small, often white
• Stamens laminar-like

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Austrobayileales
Nymphaeales
Stamens in the basal grades
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• Pollen monosulcate
• Carpels ascidate conduplicate with a
  postgenital plug

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• Pollination probably entomophilous??
• Fruits woody (but soon becoming fleshy and
  edible dispersed by forest animals)
• Lived in darkish, disturbed areas of wet
  tropical forests

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• Some authors have suggested an aquatic origin
  for the angiosperm
• However, it may be more appropriate to see the
  waterlily clade as being highly modified for the
  aquatic environment
• As a result, many characters are ? probably
  adaptations to watery environments rather than
  representative of a primitive condition

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• The herbaceous condition (i.e. the paleoherbs)
  is probably likewise advanced secondary
• The large trees of the Magnoliales, with their
  large, polymerous flowers also probably represent
  a dervived condition