Please enable JavaScript.
Coggle requires JavaScript to display documents.
Vascular Plants w/out seeds. (Megaphyll Evolution (Origin of Megaphylls (3…
Vascular Plants w/out seeds.
Early Vascular Plants
Rhyniophytes
Earliest fossils that belonged to land plants were
Cooksonia
, a genus of extinct plants.
Cooksonia
characteristics
No leaves
Equal dichotomous branching
Upright stems
Epidermis with a cuticle
Simple bundle of Xylem
Ends of branches contained large masses
Homosporous
All plants that have the same characteristics as
Cooksonia
are classified as Rhyniophytes.
Rhynia
and
Aglaophyton
were other early vascular plants similar to
Cooksonia
.
They, of course, shared many similar characteristics.
Zosterophyllophytes
Named after principal genus
Zosterophyllum
Small herbs without secondary growth.
Features
3 important distinctions
Sporangia opened transversely along top edge
Xylem was an exacrh protostele (protoxylem on outside, metaxylem in center).
Sporangia were lateral.
Some of the simplest vascular plants alive today may indeed represent a line of evolution based on
Zorosterophyllum
.
Many were similar to Rhyniophytes.
Microphyll Evolution
Extant Genera
Selaginella
Easily mistaken to be mosses.
Best known species is the resurrection plant.
S. lepidophylla
Curls up, turns brown, and appears dead upon drying. Uncurls and regreens when moistened.
Less common in temperate North America
Heterosporous
May be distinguished by a small flap of tissue known as the ligule, located on the leaves.
Isoetes
Genus of about 60 species.
Mostly small, unusual plants called quillworts.
Growth occurs in wet, muddy areas that occasionally become dry.
Body consists of a corn-like stem with roots attached below and leaves above.
Similariteiies to
Selaginella
Microphylls also have ligules.
Heterosporous
Stylites
Very similar plants to
Isoetes
Several botanists seem to suggest that these are merely extreme forms of
Isoetes
.
Lcyopodium
is fairly common in forests from tropical to arctic regions.
200 living species
Small herbs with true roots and short, upright, branches.
Microphylls are spirally arranged on stems.
All species are homosporous.
Morphology
Earliest lycophytes were members of the genera
Drepanophycus
and
Baragwanathia
.
Similar to their ancestors, zosterophyllophytes, with one major difference (below).
#
Enations were large, up to 4cm in length. It contained a single trace of vascular tissue.
May, technically, be called "leaves".
In reality, these are named microphylls for clarity.
Not the line of evolution that led to ferns and seed plants.
True roots evolved, allowing lycophyte sporophytes to anchor, absorb, and grow far more efficiently.
Extinct Lycophyte characteristics and names.
Names
Sigilaria
Stigmaria
Lepidodendron
Characteristics
Vacular cambium
Secondary Growth
Wood was very similar to modern day pines.
Megaphyll Evolution
Origin of Megaphylls
3 distinct types of homoplasic structures
Enations/microphylls
Megaphylls
Leaves on gametophytes of nonvascular plants
Evolved from branch systems and are present in all seed plants.
Evolution summed up as the telome theory
The leaves we see on trees are a result of around 300 million years of evolution.
By far the most common type of plant.
Monilophytes
Many are ferns.
One of two sister clades under euphyllophytes
The other clade related is lignophytes
United by 3 synapomorphies
They have megaphylls.
They have a 30-kilobase inversion in the large single-copy region of their plastid DNA.
Roots have exarch xylem.
Trimerophytes
This division was proposed in 1968 for three genera of extinct plants (below).
Genera of extinct plants
Trimerophyton
Psilophyton
Pertica
Fossils strongly resemble rhyniophytes.
#
Became distinct during the Lower Divonian.
Unique characteristics
Overtopping
Unequal branching where one stem was more vigorous.
Pseudomonopoidal branching
A single main trunk.
Small lateral branches, some fertile, bearing sporangia, and some sterile.
Equisetophytes
Classified as division Arthrophyta
Consist of several extinct plants and one genus.
Equisteum
15 extant species known as horsetails or scouring rushes.
The living plants have no secondary growth.
#
Usually less than 1 meter tall.
Reproductive structures are very specialized.
