Angiosperm Evolution

Chapter 6Simpson, 2nd Edition

Major Evolutionary Advances

Flowers – 130 mya

5,000mya

4,000mya

3,000mya

2,000mya

1,000mya

EarthForms

ProkaryoticCells

EukaryoticCells

MulticellularPlants

Vascular

tissue

Seeds

Flowers

Life - 3,800 myaProkaryotic cell/autotrophic

Eukaryotic cell - 1,400 mya

Multicellar plants - 1,000 mya

Vascular tissue - 430 myaNeeded on land - why?

Seeds - 350 mya

1. Earth2. Prokaryotes3. Eukaryotes4. Multicellular life5. Vascular tissue6. Seeds7. Flowers

TimelineDevonian Period

• 400mya – 1st vasc plts• Psilotum – like

Devonian-Carboniferous• ferns, lycophytes,

sphenophytes & progymnosperms

Mesozoic• gymnosperm-dominant seed

plants

Cretaceous Period• 130 mya 1st fossil flowers• 90 mya - worldwide

angiosperm dominance

Relationships of Angiosperms

Bennettitales and Genetophytes – 225 mya

Relationships of Angiosperms

Systematics

• phylogeny represented by cladogram (phylogenetic tree• branching diagram that

conceptually represent the evolutionary pattern of descent

• lines represent lineages, with implied time scale

• branch = divergence• ancestral = preexisting• apomorphy = derived

(evolutionary novelty)

Systematics• Phylogenetic Systematics

(cladistics)• methodology to infer

evolutionary history using apomorphies

• recognizes monophyletic groups (= clade)

• Phylogenetic Classification Scheme can result

• avoids:• paraphyletic groups

• com anc but not all descendants

• polyphyletic groups• two or more sep groups with sep anc

Angiosperm Systematics

What conclusions can be drawn from this cladogram?

Angiosperm Apomorphies1. flower, usually with

perianth

Angiosperm Apomorphies2. stamens with 2

lateral thecae, each composed of 2 microsporangia

3. reduced, 3-nucleate male gametophyte

Angiosperm Apomorphies4. carpels and fruit formation

• conduplicate (inwardly folded longitudinally & along the central margin) megasporophyll bearing 2 adaxial rows of ovules

• carpel body encloses seed (angiosperm name origin)

Angiosperm Apomorphies5. ovules with 2 integuments• bitegmic with micropyle at distal end

Angiosperm Apomorphies6. reduced, 8-nucleate female gametophyte

Angiosperm Apomorphies6. reduced, 8-nucleate female gametophyte:• evolution of female gametophyte

Angiosperm Apomorphies7. endosperm formation• product of double fertilization• zygote = 1 sperm + egg• endosperm = 1 sperm + polar nuclei

Angiosperm Apomorphies8. sieve tube members• sieve plates – contain pores at end walls

larger than lateral pores• sieve cells are primitive sugar-conducting

cells

vessels found in all but primitive angiosperms

Archaefructus 130 mya northern China

reconstruction of Archaefructus sinensis fossil imprint of Archaefructus lianogensis

Origin of Angiosperms

Four evolutionary trends among flowers

1. floral parts many -> few2. floral whorls from 4, long floral axis,

separate parts -> reduced whorls, short floral axis, fused parts

3. superior -> inferior ovary4. symmetry radial -> bilateral

1. floral parts few2. reduced whorls,

short floral axis, fused parts

3. inferior ovary4. bilateral

symmetry Anemone

Lonicera (honeysuckle)

Nelumbo (Lotus)

Helianthus disk floret

Vanilla (vanilla bean orchid)

Order AsteralesAsteraceae

(=Compositae)Sunflower Family1620 genera23,600 species

1) most diverse dicot family 2) 98% herbaceous, but

shrubs, trees or vines also

3) inflorescence a head, subtended by involucre of phyllaries

4) K 0-∞ C (5) [4] or (3) A (5) [(4)] G (2) inferior

Order AsteralesAsteraceae

(=Compositae)Sunflower Family1620 genera23,600 species

p. 429Fig. 8.131

Order AsteralesAsteraceae

(=Compositae)Sunflower Family1620 genera23,600 species

p. 430Fig. 8.132

Order AsteralesAsteraceae

(=Compositae)Sunflower Family1620 genera23,600 species

p. 431Fig. 8.133

Order AsteralesAsteraceae

(=Compositae)Sunflower Family1620 genera23,600 species

p. 432Fig. 8.132