Coniferophyta

Gymnosperms
Spermatophytes
•It is the group that includes seed-producing plants.
•The seed contains embryo, protects it during adverse
conditions and contains all nutrients needed for the
seedling development.
•They show microscopic gametophytes.
•They do not need anymore of water for reproduction.
Male gametophyte (polle grain) is released at maturity and
dispersed by wind, insects or animals.
•They comprises Gymnospermes (plants with ovule/seed
naked) and Angiosperms (flowering plants with
ovule/seed protected by ovary).
Gymnosperms
•They are seed plants in which the ovules are carried naked on
the cone scales, in contrast to the angiosperms, in which they are
enclosed by an ovary.
•Gymnosperms date from the Carboniferous (360-290 millions
years ago) and subsequently they dominated the floras of the
world until the Cretaceous (65 millions years ago), since when
they have been progressively displaced by the angiosperms
(flowering plants).
•‘Gymnosperm’ is used only informally to describe what are now
classified as 4 separate divisions: Cycadophyta (100 species),
Ginkgophyta (1 living fossil species), Coniferophyta (550 species),
Gnetophyta (70 species).
•Although they comprises only 720 species, they form the
dominant vegetation in large areas of the world (e.g. taiga = forest
of conifers).
•Numerous species are used for pharmaceutical purposes,
notably conifers for the preparation of resin derivatives employed
in the treatment of respiratory disorders.
Gymnosperms
•They are heterosporous plants, bearing megasporangia (ovules)
producing megaspore retained inside the sporangium (endosporic
development); they give rise to the female gametophyte, and
microsporangia producing microspores that give rise to the male
gametophyte (pollen grain).
•Ovule is composed of a central mass of tissue (nucellus), surrounded
by 1 or 2 protective layers (integuments), which eventually give rise to
the seed coat. Within the nucellus is a large structure, the embryo sac,
which has developed from the megaspore and contains the naked egg
cell. Nucellus bears a canal in the coverings called micropyle through
which the pollen tube usually passes during fertilization; later, when the
seed matures and starts to germinate, the micropyle serves as a minute
pore through which water enters.
•Seed is a fertilized ovule, composed of integuments, embryo and
nutritive substances. It replaces spore as diffusion unit.
•Fertilization is not more linked to the presence of water: male
gametophyte (pollen grain), transported to the female gametophyte
inside the ovule, emits the pollen tube releasing the male gamete
(without flagella) directly to the female gamete.
Gymnosperms
•Pollination is the transfer of pollen grains from male to female
gametophytes or from micro- to macro-sporangium. This process
facilitates contact between male gametes and the female ovum, leading
to fertilization, development of seed, and thence a new plant.
Gymnosperms have anemophilous pollination.
•In gymnosperms, the pollen tube developing from a pollen grain
grows down and penetrates the neck of the archegonium, facilitating
contact between the sperm cells (male gametes) and the ova (female
gametes).
•Most archegonia contain many ova, so that multiple fertilization can
occur, although only 1 sperm can fertilize an egg cell.
•Unlike angiosperms, which do not possess archegonia, pollen cones
and seed cones mature at different times within a season, so that there
is usually a long interval between pollination and fertilization.
•Gymnosperm have an alternation of 2 heteromorphic generations with
large sporophytes (dominant) and microscopic, dipendent
gametophytes (only 4 cells in the male gametophyte).
•Gymnosperms consist of tree or shrubs, anyway woody
plants possessing secondary thickening by vascular and cork
cambium.
•They have homoxil wood with only tracheids having
conducting and supporting functions.
briophytes and pteridophytes
spermatophytes (gymnosperms and angiosperms)
Relations between gametophyte and sporophyte
ovule
•Ovule is a megasporangium containing a megasporocyte
that undergoes meiosis giving 4 haploid cells: one is the
megaspore, while the other 3 degenerate.
•The megaspore gives rise to the femal gametophyte,
containing nucellus with one or more archegonia; so, more
than one egg cell may be fertilized, but only one embryo may
survive. Nucellus is composed of a nutritive tissue feeding
embryo during ontogeny.
female gametophyte
•Different stages leading to the fertilization of the egg cell. In gymnosperms,
pollination is known as micropylar, because the pollen grain attaches directly
to this canal of the naked ovule. Female gametophyte and so embryo
develop inside parent sporophyte (endosporic development).
•Ovules and seeds are unprotected and beared on the
external surface of specialized leaves known as
megasporophylls that in conifers are grouped in cones or
strobila.
•Cones are groups of closely
packed sporophylls arranged
around a central axis.
•Each microspore germinates to form the male gametophyte, a
structure made up of winged pollen grains (for wind pollination)
containing 2 protallial cells, one generative cell (forming 2 sperms) and
one tube cell (generating the pollen tube). In gymnosperms there are
not antheridia (water is no more needed for reproduction).
•The pollen grain contains 3 haploid nuclei (a tube nucleus and 2
sperm nuclei), which pass down the pollen tube to the ovum. One
of the sperm nuclei fertilizes the ovum, and the second
degenerates as well as the tube nucleus.
•Seed of conifers is composed of 2 diploid generations (the outer integuments
and the embryo) and one haploid generation (food store tissue).
•Embryo is composed of an hypocotyl-root axis with a root cap protecting root
merystems and an apical meristem to the endings. Gymnosperm have usually
numerous cotyledons.
Life cyle of a pine
CONIFEROPHYTA
•The biggest division of gymnosperm, with a long fossil history,
comprising trees (e.g. sequoia) and shrubs (e.g. juniper), nearly all
of which are evergreen, commonly with monopodial crowns.
•The leaves are often needle- or scale-like.
•Branches with short (brachyblasts) and long shoot (macroblasts).
•The wood (homoxil) lacks vessels (trachea); only tracheids with
areolate pits.
•Most conifers are resinous due to the presence of resin canals.
•Fertile parts occur in unisexual cones, variously containing sterile
scales.
•The ovule and seed are naked and borne on a scale.
•Are important for timber and paper production.
•There are about 550 extant species.
CONIFEROPHYTA
CONIFEROPHYTA
branch of pine with mature
and young ovuled cones
CONIFEROPHYTA
branch of pine with male cones
(bearing microsporangia)
CONIFEROPHYTA
ovuled cones
male cones
CONIFEROPHYTA
ovuled cones of fir
CONIFEROPHYTA
ovuled cones of larch
CONIFEROPHYTA
ovuled cones of cypress
CONIFEROPHYTA
ovuled cones of juniper
CONIFEROPHYTA
t.s. of a pine leaf
CONIFEROPHYTA
t.s. of pine stem
(secondary thickening)
•The wood of conifers is composed only of tracheids (homoxil
wood), while phloem is composed only of sieve cells.
CONIFEROPHYTA
•Yew seeds surrounded by arils (no cones) that
aid seed dispersal by providing food as an
attractant and reward to the dispersers.
•Yew is a dioecious plant, with male and
ovuled cones on separate individuals.
CONIFEROPHYTA
•Giant sequoia of California; it
can reach about 80 m of height
and a weight of 1800 tons.
CYCADOPHYTA
•Cycaodophyta is a division of gymnosperms comprising plants with
leaves and habit similar to those of palm trees, although some species are
quite small.
•Cycads are dioecious, and most bear large, coloured, female or male
cones.
•Pollen grains have motile spermatozoa within them, which is a very
primitive feature. Cycads have enthomophilic pollination.
•Formerly they were much more important and, following their
appearance in the Permian (350-300 millions years ago), remained
important members of the world’s Mesozoic floras (up to 65 millions years
ago). Their reduction as marked in the late Cretaceous as they were
progressively displaced by angiosperm trees.
•There are 9 or 10 genera, and about 100 extant species. All are tropical or
subtropical.
CYCADOPHYTA
Ovuled cones of an African Cycad
seeds of Cycas
CYCADOPHYTA
•4 genera are
American; 5 are Old
World (Australian and
south-eastern African)
GINKGOPHYTA
•The division of gymnosperms that includes
only the extant Ginkgo biloba (maidenhair tree)
and its extinct relatives. They first occurred in
Triassic (250-200 millions years ago) and in the
subsequent Jurassic Period (200-150 millions
years ago) their distribution was practically
worldwide.
•The surviving species is restricted in the wild
to China, and its leaves are strikingly similar to
fossil Ginkgo leaves from the Triassic.
•The restricted geographical range, the
unchanged appearance of the leaves, and the
motile male sperms have together led to the
maidenhair being referred to as a ‘living fossil’.
GINKGOPHYTA
•Gynkgo biloba is a dioecious, deciduous
tree native to China, bearing fan-shaped
leaves with open dichotomous venation.
The naked seed is oily and edible but the
embryo is bitter. It is widely cultivated.
primitive fertilization occurring
in Ginkgo and Cycas
flagella
GNETOPHYTA
•A remarkable and probably artificial division of gymnosperms
that comprises only the Gnetales. There are 3 constituent genera,
embracing trees, shrubs, and lianes (Ephedra and Gnetum), and
even turnip-like plants (Welwitschia).
•They show some features being referred to as the closest living
relative of angiosperms. These are:
•strobyla similar to inflorescences;
•ovule within the perianth tube of flower-like structures;
•absence of archegonia;
•tentative of double fertilization (without the formation of
endosperm);
•enthomophilic pollination (production of nectars);
•presence of trachea into xylem;
•leaves in some cases similar to those of angiosperms.
GNETOPHYTA
The sole genus, with 28 species, of the pantropical
gymnosperm family Gnetaceae, of which 26 species are
woody climbers with gouty nodes, and 2 are trees. They
are dioecious, and often cauliflorous. The seeds are naked,
borne on racemes, and edible in many species.
hard leaves of Gnetum, similar
to those of Angiospems
GNETOPHYTA
b
a
Ephedra nebrodensis
Ephedra sinica
•Ephedra is a genus of shrubs which have scalelike leaves and whip-like, slender green stems.
Their ovule is naked within the perianth, which
becomes woody around the seed. There are 40
species, found in the warm temperate regions of
each hemisphere.
GNETOPHYTA
•Welwitschia, the sole genus, with only one species (W. mirabilis) of the
remarkable gymnosperm family Welwitschiaceae of the deserts of southwestern Africa. It has a barrel-like stem with a deep tap root, bearing on its rim
big, tattering, strap-like leaves, and ovules within the perianth tube of the
female ‘flower-like’ structure.