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Vascular Plants w/out Seeds (The Megaphyll Line of Evolution (Origin of…
Vascular Plants w/out Seeds
Early Vascular Plants
Rhyniophytes
Xylem Structure
Protostele
Solid mass of xylem
No Pith
Endarch Protostele
Protaoxylem in center
Metaxylem differentiates
Small Narrow Cells
Exarch Protostele
Metaxylem in center
Protoxylem on edges
Siphonostele
Pith in center
Equal dichotomous branching
Equal sized branches
Zosterophyllophytes
Sporangia are lateral
Sporangia opened transversely
Xylem Exarch Protostele
Protoxylem on outer margin
Metaxylem in center
Morphological changes quickly evolve
Enations
Outgrowths
Quite small to long
Thin scales
Increase photosynthetic surface area
The Microphyll Line of Evolution
Morphology
Microphylls
Enations
Evolution of true roots
Large Enations
Up to 4 CM
Single well developed vascular tissue
Heterospory
Cones or Strobili
Sporangia cluster
Compact groups
Microspores & Megaspores
Precondition
Evolution of Seeds
Extant Genera
Microphylls spirally arranged
Secondary growth never occurs
Sporangia arranged in cones
Spores germinate
Grow into bisexual gametophytes
Produce Antheridia & Archegonia
Ligule
Small flap of tissue
On upper surface of leaves
Simple Structures
Adaptive Advantages Unknown
The Megaphyll Line of Evolution
Trimerophytes
Overtopping
Unequal branching
One Stem more vigorous
Pseudomonopodial Branching
Single main trunk
Small lateral branches
Branch Positioning
More Regular & Controlled
Origin of Megaphylls
Megaphylls
Leaves evolved from branch systems
Present in all seed plants
Telome Theory
Sporophyll
Sporangium-bearing
Leaf-Like Structure
Euphyllophytes
Monilophytes
Roots have exarch xylem
Megaphylls present
30-kilobase inversion
Lignophytes
Woody Plants
Equisetophytes
Horsetails or Scouring Rushes
Monopodial Growth
Main Trunk
Lateral Branches
True Leaves
True Roots
Ferns
Eusporangia & Leptosporangia
Eusporangium
Surface Cells
Undergo Periclinal Divisions
Small Plate Cells
Outer Cells
Sporangium Wall
Inner Cells
Sporogenous Tissue
Leptosporangia
Surface Cells
Small Outward Protrusion
Psilotum & Tmesipteris
Psilotum
Highly Derived
Highly Simplified Ferns
Small Plants
Prostrate Rhizomes
Upright Stems
