Everything about Gymnosperm totally explained
Gymnosperm (Gymnospermae) are a group of
spermatophyte seed-bearing
plants with
ovules on the edge or blade of an open
sporophyll, which are usually arranged in cone-like structures. The other major group of seed-bearing plants, the
angiosperms, have ovules enclosed in a
carpel, a sporophyll with fused margins. The term gymnosperm comes from the Greek word
gumnospermos, meaning "naked seeds" and referring to the unenclosed condition of the seeds, as when they're produced they're found naked on the scales of a cone or similar structure. There are between 700 and 900 species of Gymnosperm. Often they're used for many economical uses and as folk medicines. Some common uses for them are
soap,
varnish,
lumber,
paint, edible plants, and
perfumes.
Gymnosperms are
heterosporous, producing
microspores that develop into
pollen grains and
megaspores that are retained in an ovule. After fertilization (joining of the micro- and megaspore), the resulting embryo, along with other cells comprising the ovule, develops into a seed. The seed is a sporophyte resting stage. Reproduction in gymnosperms varies greatly.
Cycads and
Ginkgo have motile sperm that swim directly to the egg inside the ovule, while
conifers and
gnetophytes have sperm with no
flagella that are conveyed to the egg along a
pollen tube which grows through ovule tissue.
In early classification schemes, the gymnosperms (Gymnospermae) "naked seed" plants were regarded as a "natural" group. However, certain fossil discoveries suggest that the angiosperms evolved from a gymnosperm ancestor, which would make the gymnosperms a
paraphyletic group if all extinct taxa are included. Modern
cladistics only accepts taxa that are
monophyletic, traceable to a common ancestor and inclusive of all descendants of that common ancestor. So, while the term 'gymnosperm' is still widely used for non-angiosperm seed-bearing plants, the plant species once treated as gymnosperms are usually distributed among four groups, which can be given equal rank as divisions within the Kingdom Plantae.
Molecular
phylogenies of extant gymnosperms have conflicted with morphological datasets with regard to whether they comprise a
monophyletic group or a
paraphyletic one that gave rise to angiosperms. At issue is whether the
Gnetophyta are the
sister group of angiosperms, or whether they're sister to, or nested within, other extant gymnosperms. Numerous fossil gymnosperm
clades once existed that are morphologically at least as distinctive as the four living gymnosperm groups, such as
Bennettitales,
Caytonia and the glossopterids. When these groups are considered the question of gymnosperm and angiosperm relationships becomes even more complicated.
Further Information
Get more info on 'Gymnosperm'.
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