Page 154 - Biology_F5

Comparative studies of natural groups of organisms
(b) Cycads, the palm like plants.
(c) Ginkgo, examplified by only one
extant species, the Gingko biloba,
which is regarded as a living fossil,
because the majority of species in this
division are extinct.
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(d) Gnetos, such as Welwitschia mirabilis.
restricted to deserts in Namibia and
Angola.
Figure 3.26: A photo of cypress tree among the
popular Christmas tree
Source: TAFORI, 2019
Species belonging to this division are
evolutionarily, more advanced than
pteridophytes. They have more advanced
vascular tissues, and they do not require
water for fertilisation. The presence of
a highly reduced gametophyte and seed
formation also makes them evolutionarily
more advanced than ferns. Coniferophytes
are very abundant in the cold and moist
regions, such as the southern highlands (a) The plants bear cones from which
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and along the slopes of Mount Kilimanjaro
in Tanzania. Globally, coniferophytes are
common in the North-western part of the
United States, the northern hemisphere,
and China.
Characteristics of division
Coniferophyta
(a) They are non-flowering, seed bearing
plants, producing naked seeds, which
are not enclosed in ovaries or fruit
tissues.
(b) Sexual reproduction involves
microspores (male gametophyte) and
megaspores (female gametophyte),
which are found in male and female
cones or strobili, respectively.
(c) Fertilisation does not require water;
instead, they develop pollen tubes,
which carry sperms to the ovule for
fertilisation.
(d) They have poor xylem with only
tracheids as conducting elements but
no vessel elements. This is the reason
why most coniferophytes produce soft
wood.
(e) Their phloem tissues lack companion
cells; instead, they are associated with
albuminous cells.
(f) Leaves are reduced into spiny or
needle-like leaves to minimise water
loss through transpiration. Exceptions
are Gingkos and Cycads.
Distinctive features of division
Coniferophyta
Presence of the following features in
members of division Coniferophyta
differentiate them from members of other
divisions:
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