Chapter 21
the microphyll line of evolution: lycophytes
the megaphyll line of evolution: euphyllophytes
early vascular plants
zosterophyllophytes
morphology
heterospory
extant genera
trimerophytes
origin of megaphylls (euphylls)
monilophytes
ferns
rhyniophytes
earliest fossil of a vascular land plant was the cooksonia
no leaves
equal dichotomous branching
both branches being equal size and vigor
have an epidermis and cuticle
a cortex of parenchyma
simple bundle of xylem comprised of tracheids with annular secondary walls
xylem structure of early vascular plants
short cylinders
center is solid mass of xylem with no pith
endarch prostele
this is called a protostele
protoxylem is in the center and metaxylem differentiates on the outer edge
siphonostele
pith is present in the center
occurs in ferns and seed plants
small herbs with no secondary growth
similar to rhyniophytes
grew as small bunches
3 distinct ways it isn't
sporangia were lateral
sporangia opened transversely along the top edge
xylem was an exarch protostele
most have smooth surface but others had enations
enations in the division Lycophyta are called microphylls for clarity
another important advance was the evolution of true roots
as wood grew to a larger circumference, cambial cells increased wider tangetially
extinct and extant lycophytes sporangia are grouped compactly called cones or strobili
this protects them
many species have remained homosporous, others became heterosporous
lycopodium is fairly common in forests of tropical regions
ground pine or club moss
all species have true roots and short upright branches
microphylls are spirally arranged on their stems
all are homosporous
selaginella
less common in temperate north america
plants are smaller and mistaken for moss
known as the resurrection plant
can be distinguished by a small flap of tissue on the upper surface of the leaves
called the ligule
isoetes is a genus of 60 species of small plants call quillworts
grown in wet muddy areas
small corm-like stem that has roots attached below and leaves above
overtopping is a big issue because of unequal branching
pseudomonopodial branching
single main trunk rather than a series of dichotomies
leaves evolved from branch systems and are present in all seed plants, ferns, and equisetophytes
evolution is summarized by telome theory
sporophyll
a sporangium-bearing, leaf-like structure
telomes
ultimate twigs, those of last dichotomy
webbing
the parenchyma that develops between telomes and even lower branches
otherwise known as euphyllophytes
woody plants
lignophytes
horsetail differs from other ferns
equinsetophytes
sister to the ferns
umbrella shaped sporangiophore
monopodial growth
main trunk, lateral branches, true leaves
first appeared in the Devonian Period
over 12000 species
almost all are leptosporangiate ferns
leaf trace diverges from the siphonostele
leaves a small segment of vascular cylinder of parenchymna, called the leaf gap