Vascular Plants without Seeds (The Megaphyll Line Of Evolution:…
Vascular Plants without Seeds
Early vascular Plants
Equal dichotomous branching
Both branches being of equal size and vigor.
Xylem structure of Early vascular plants
The center is a solid mass of xylem with no pith.
Protoxylem is located in the center and metaxylem differentiates on the outer edge of the xylem mass.
Metaxylem is located in the center of the xylem mass and protoxylem on the edges as several groups next to the phloem
Pith is present in the center.
Sporangia are lateral
Sporangia open transversely along the top edge.
Sporangial walls are several layers thick and same size.
The Microphyll Line of Evolution: Lycophytes
They represent the ancient line of evolution distinct from seed plants
Sellaginellas can be distinguished from lycopodiums by a small flap of tissue , the ligule, on the upper surface of Selaginella leaves.
Cones or strobili
clusters of sporangia
The Megaphyll Line Of Evolution: Euphyllophytes
Trimerophytes has an unequal branching in which one stem is more vigorous.
Pertica displays pseudomonopodial branching
Origin of Megaphylls (Euphylls)
Three distincts types of homoplasic structures called leaves occur in plants.
leaves on gametophytes of non vascular plants
enations of zosterophyllophytes and lycophytes
also known as ferns
horsetails or scouring rushes
The term vascular cryptogams
refereed as vascular cryptogams
Dibiontic life cycle
Have only one multicellular generation
Monobiontic life cycle
Life cycle with alternation of isomorphic generations.
After dibiontic life cycle originated.
Both gametophyte and sporophyte becomes larger, more complex and vascularized.