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Vascular Plants w/o Seeds (Early+Vascular+Plants_+Extinct+Rhyniophytes …
Vascular Plants w/o Seeds
Early Vascular Plants
Rhyniophytes
Characteristics
naked stems
epidermis with cuticle
cortex of parenchyma
simple bundle of xylem composed of tracheids
Cooksonia
: genus of extinct plants
equal dichotomous branching
both branches equal size and vigor
Xylem structure of early vascular plants
two types of xylem organization
protostele
in both, center is solid mass of xylem with no pith
endarch protostele
protoxylem located in center
metaxylem differentiates on the outer edge of xylem mass
exarch protostele
metaxylem located in center of xylem mass
protoxylem on edges as several groups next to the phloem
Later evolved stele
siphonostele
pith is present in center
Occurs in stem of ferns and
seed plants
Zosterophyllophytes
small herbs w/o secondary growth
3 characteristics make them distinct
lateral sporangia, not terminal
sporangia opened transversely along top edge
xylem was an exarch protostele
protoxylem on outer margin
metaxylem in center
The Microphyll Line of Evolution:
Lycophytes
Morphology
lycophytes
large enations; up to 4cm long
contained single well-developed trace of vascular tissue
Microphylls
enations in Lycophyta
vascular cambium cells can't undergo radial longitudinal division
makes them dif. from pines
Heterospory
necessary precondition for evolution of seeds
cones/strobili
compact groups of sporangia clustered together
The megaphyll Line of Evolution:
Euphyllophytes
Trimerophytes
features that separate them from rhyniophytes
Overtopping
most important
ability of one shoot to grow for a longer time than the other shoot that resulted from the branching
Pseudomonopodial branching
single main trunk rather than a series of dichotomies
Origin of Megaphylls (Euphylls)
3 distinct types
1) leaves on gametophytes of nonvascular plants
2) enations/microphylls of zosterophyllophytes and lycophytes
3) megaphylls: leaves that evolved from branch systems and are present in all seeds plants, ferns, and equisetophytes
Telome Theory: summarizes megaphyll evolution
Telomes
ultimate twigs, those of last dichotomy
Equisetophytes
one genus, several genera of extinct plants
15 extant species
Horsetails
Scouring rushes
living plants are all herbs
no secondary growth
usually less than 1 m tall
Ferns
can be found in almost any habitat
appeared in Devonian period
mostly all homosporous
Monilophytes
two sister clades
euphyllophytes are united by 3 synapomorphies
1) their roots have exarch xylem
2) they have megaphylls
3) they have a 30-kilobase inversion in the large single-copy region of their plastid DNA
The Term "Vascular Cryptogams"
Informal name
also often called ferns and fern allies
name indicates they have vascular tissue
because they lack seeds, their reproduction is hidden
Lack
seeds
Flowers
Fruits
Etc
