2001: A Plants without Seeds Odyssey

Michael Patterson, Rebecca Flanagan, and

Kellie O’Hearn

1. Evidence of Early Plant Evolution2. Monophyletic, Clade, and Synapomorphies3. Evolved Nonvascular Features4. Plant Life Cycle5. Moss Life Cycle6. Vascular Plants7. Evolved Vascular Features8. Vascular Plants9. Nonvascular Analogous Structures10. Homospory and Heterspory11. Nonvascular Plant Clades12. Vascular Plant Clades13. Water14. Evolution of Plants

Scene Selection

1870Dawson• discovered Psilophyton,

means “naked plant”

Kidston and Lang• discovered similar “naked

plant” fossils, named genus Rhynia

1915

Reconstruction of extinct Psilophyton

Reconstruction of Devonian period

Rhynie chert

Evidence of Early Plant Evolution

A monophyletic clade shares synapomorphies.

Ten groups: 7 vascular and 3 nonvascularSynapomorphy of vascular clade: tracheidsNonvascular: No clade

Evolved Nonvascular Features

Evolutionary adaptations have granted nonvascular plants global, widespread existence. Waxy Cuticle & Water

Open Stomata

Gametophytes/Gametangia of the liverwort Marchantia

Plant Life CycleMitosis vs. Meiosis:

Mitosis – formation of gametophytes, sporophytes,

and gametesMeiosis – formation of spores

Gametophyte vs. Sporophyte

Gametophyte – most prominent stage in nonvascular

plantsSporophyte – most prominent

stage in vascular plants

Haploid vs. Diploid:Haploid – one copy of

chromosomesDiploid – two copies of

chromosomes

Antheridium – MArchegonium – F

Rhizoid, Protonema, Bud?

Specific to Mosses

Protected Embryo

Gametophyte vs. Sporophyte

Gametophyte – most prominent stage in nonvascular plants

Sporophyte – most prominent stage in vascular plants

Vascular Plants

Synapomorphy of vascular clade: tracheids

Tracheid – a type of cell that is the preeminent carrier of water of the xylem

PhloemXylem

“Pathway for Transport”

“Rigid Structural Support”

Evolved Vascular Features“Branching, Independent Sporophyte”

A vascular lycophyte sporophyte

Rhizoids and Rhizomes

Evolution

RootsMicrophyll (Simple Leaf)

Vascular PlantsMegaphyll (Complex Leaf)

Adiantum (fern)

Lycopodium (club moss)Stomata

Nonvascular Analogous StructuresVascular Nonvascular

Stems, xylem and phloem Small growth pattern, capillary action and diffusion

Roots and leaves, acquisition of nutrients and products of

photosynthesis

Symbiotic relationship with fungi, facilitating absorption of

water and nutrients

Homospory & Heterospory

HeterosporyHomospory

Nonvascular Plant Clades

Left: Leafy GametophyteRight: Thalloid Gametophyte

Short sporophytesSmall sporangia

Liverworts

Possess stomata

Primitive ‘vascular system’:

Leptoids – sugarHydroids – water

Protonema -> Buds -> Apex -> Sporangia

Mosses

Hornworts

Simple gametophytes

Large, plate-like chloroplasts

Lack of transport system

Symbiotic fungal relationship

Vascular Plant Clades

Lycophytes

Dichotomous roots

Microphylls

Sporangia – Structures called Strobili, Sporophylls

Horsetails

Megaphylls

Whisk Ferns

Small Scales or Small Megaphylls

Gametophytes live underground, rely on

symbiotic relationship with fungi

Leptosporangiate ferns

Sporangia appear on stalk, undersides of leaves in bundles

called Sori

Possess true leaves, roots, and stems

Megaphylls

Only lycophytes have dichotomous roots.

All seedless plants (both nonvascular and vascular) require water in order for the sperm to successfully

reach the egg.

The Evolution of Plants

ReferencesSadava, David, et. al. Life: The Science of Biology. Sunderland: Sinauer Associates, 2011. Print.

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