Fossil lycopods

Fossil lycopods
Lycopodiales-like
Isoetales-like
(Order: Lepidodendrales)
Review of
Basal Vascular Plants
Phylogeny of basal Polysporangiophytes
Lycophytes
Lycopsida
Zosterophyllopsida
Lycophytina
Euphyllophytes
Trimerophytes
Seed Plants
Progymnosperms
Equisetophytes
Ferns
Psilotophytes
Euphyllophytina
Zosterophylls
Trimerophytes
Vascular Tissue (Tracheids)
Rhyniophytes
Aglaophyton
major
Branching axes with sporangia
Banks, 1968
T
Z R
(Trimerophytes)
(Cooksonia, Rhynia)
Diversity of Vascular Plants
Basal Diversity
Lycophytina
Euphyllophytina
(Trimerophytes)
Zosterophylls
Trimerophytes
(Cooksonia, Rhynia)
Rhyniophytes
Banks, 1968
Summary of Plant Evolution
Asteroxylon
from the
Rhynie chert
Asteroxylon mackiei
Microphylls of
Asteroxylon mackiei
Leaf Arrangement (helical)
Leaf Trace (only to leaf base)
Origin of the microphyll – enation theory
Enation
random arrangement
no vascular bundle
Microphyll
definite arrangement
vascular bundle
Lycopodium
Rhyniophytes-Silurian e.g. Cooksonia Asteroxylon –Devonian Rhynie Chert
Sawdonia-Devonian zosterophyll
Lower/Middle Devonian landscape
Order: Lepidodendrales
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•
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Heterosporous
Arborescent
Ligulate
Carboniferous - dominant plants
@300 million yrs. b.p.
• Up to 40 m tall
Coal forming swamps
• Coal = compressed plants
• Coal balls = calcium carbonate nodules
containing permineralized plant parts,
studied using the cellulose acetate peel
technique
• 3 dimensional preservation of these
plants; therefore, we know a lot about
them
Classic coal swamp diorama, Field Museum in Chicago
Stems
Coal swamp lycopod
growth
Lepidodendron & Lepidophloios
highly branched
Sigillaria branched once or twice
Stems
Stem Surface
Leaf cushions have diagnostic shapes
for genera of trees
Lepidophloios
Sigillaria
Lepidodendron
Lepidophloios
Sigillaria
Stem Anatomy
Lepidodendron stem x.s.
Leaf Cushions
Leaf trace
2x
1x
Cortex
Stem Anatomy
Overlapping
Lepidophloios
Leaf cushions
cortex
Medullated protostele
mc
ic
Secondary xylem
Rooting Organ
Stigmaria underground rooting organ of all stems
Rooting Organ
Stigmaria axes with appendage scars
Rooting
Stigmarian appendages x.s.
Compare to the structure of an Isoetes root
Shoot apex
Leaf traces
stem
Isoetes root x.s.
cortex
lacuna
(air space)
Root traces
Isoetes stems are very
small and produce both
leaf and root traces in very
close proximity
phloem
xylem
Unusual structure for a root!!!!
Why are stigmarian “rootlets” not roots
but modified leaves?
• Borne in a helix like leaves at the apex
i.e., a leaf-like phyllotaxy
• Bilaterally symmetrical like leaves
• Have no root hairs
• Have an abscission layer like some leaves
• Proof from embryos
Lycopod reduction series
Sigillaria
Lepidodendron
Lepidophloios
Isoetes
Cones
Lepidostrobus
Lepidodendralean trees in
Carboniferous coal swamp
Coal Ball Peel Technique
1. Makes anatomical sections of fossil plants
2. Shows cell, tissue, and organ structure
3. Reveals that cell walls are preserved in fossils