Life on EarthKingdom Plantae

Part II

Rhyniophyta and Lycopodiophyta

Cooksonia

Introduction

• Sporophyte generation (2N) is the photosynthetic, conspicuous generation

• All members have evolved specialized tissues for water (XYLEM) and food (PHLOEM) conduction

• Groups continue to become better adapted to the terrestrial environment

Evolutionary Lines

PLANT KINGDOM

“bryophytes” “vascular

plants”

“green algae”

Evolution of Non-Seed, Vascular Plants

Early Devonian Landscape(about 400 million years ago)

Reconstructed Early Devonian Landscape

Cooksonia

Aglaophyton

Zosterophyllum

early lycophytes

Psilophyton

Phylum: Rhyniophyta• Known from fossils more

than 400 million years old (all extinct today)

• Sporophytes had no roots or leaves

• Sporangia produced only one kind of spore (homosporous)

• Example:– Rhynia (found in chert

beds in England)

Phylum: Lycophyta

• Plants with true roots and microphyllous leaves

• Some species produce compacted sporophylls into a cone or strobilus

• Some genera are homosporous (Lycopodium and Huperzia) others are heterosporous (Selaginella and Isoetes)

Heterospory vs. Homospory

male gametophyte with antheridia

female gametophyte with archegonia

or

HOMOSPOROUS PLANTS

gametophyte generation with archegonia AND

antheridia (monoecious)spores

HETEROSPOROUS PLANTS

megaspores

microspores

dioeciousgametophytes

Lycopodium

• Common in New England and the Great Lakes Region

• Often used for Christmas decorations (evergreen)

• Spores were once used as photographic flash powder

Lycopodium (strobili)

Selaginella• Species are heterosporous with

microsporangia and megasporangia

• Megaspores develop into female gametophytes

• Microspores develop into male gametophytes

• Large group with tropical, temperate and desert species

Selaginella rupestris

Selaginella with strobili

Selaginella striboli

megasporangium

microsporangium

Selaginella strobilus

Selaginella (sporangia)megasporangium microsporangium

Selaginella lepidophylla

Isoetes• Commonly known as

“quillworts”• Each microphyllous leaf is a

sporophyll, either a microsporophyll or a megasporophyll (heterosporous)

• Stem is a fleshy “corm”• Often grow at the margins of

ponds and lakes

Isoetes

Isoetes microsporangium

Isoetes

Isoetes melanopoda (Nebraska)

Lepidodendron

• Known as the fossil “scale tress”

• Common forest giant of the Carboniferous Period

• Helped to form present day coal deposits

Carboniferous Forest Reconstruction

Lepidodendron

Base of Lepidodendron (Stigmaria)