VASCULAR PLANTS WITHOUT SEEDS (THE MEGAPHYLL LINE OF EVOLUTION:…
VASCULAR PLANTS WITHOUT SEEDS
EARLY VASCULAR PLANTS
a group of extinct spore-bearing vascular plants that were leafless and rootless plants, with upright branching stems, These plants had ground-creeping rhizomes, that gave rise to upright determinate stems, have equal dichotomous branching.
a group of extinct vascular plants that lived in the Devonian period, they were small herbs without secondary growth, similar in many ways to the rhyniophytes but the arrangement of spore forming and xylem separate it from rhyniophytes.
old botanical phrase, refers to the vascular palnts that donot make seeds, cryptogams refers to the production of separate usually very small archegoniate gametophyte.
THE MICROPHYLL LINE OF EVOLUTION: LYCOPHYTES
In many extinct and extant lycophytes sporangia are clustered together in compact groups called cones which protect them, have microspore and megaspore that germinate to give rise to distinct microgametophytes and megagametophytes respectively.
microphyll are spirally arranged on their stems but secondary growth never occurs, spores germinate and grow into bisexual gametophytes that produce both antheridia and archegonia, some species have green and photosynthetic gametophyte where as some are subterranean and heterotrophic.
similar to their presumed ancestors with an important difference, their enations were large upto 4 cm long and they contain single well developed trace of vascular tissue. the enations in the division lycophyta are called microphyllls, micro means their evolution from small enations
THE MEGAPHYLL LINE OF EVOLUTION: EUPHYLLOPHYTES
ORIGIN OF MEGAPHYLLS (EUPHYLLS)
megaphyll evolution is summarized by the telome theory. the ultimate twigs, those of the last dichotomy, are known as telomes. all megaphyllous plants form a monophyletic clade, now refferd to as the euphyllophytes.
The euphyllophytes contains two sister clades, the monilophytes and the woody plants lignophytes. many monilophytes are palnts like ferns.
their fossil strongly resemble those of rhyniophytes, having terminal sporangia that dehisced laterally, homospory, dichotomous branching and an endarch vascular cylinder of tracheids. trimerophytes had an unequal branching in which one stem was more vigorous
They consist of several genera of extinct plants and one genus Equisetum with 15 extant species known as horsetails or scouring rushes. their leaves are small and have just a single trace of vascular tissue, but they are small megaphylls not microphylls.ctrue roots are present, being produced at the rhizome's nodes