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Comparative studies of natural groups of organisms

sessile, meaning that they have limited plants is alternation of generation. The
locomotion but show curvature movements. features characterising each phase of
Their vegetative body is divided into root generation are: types of spores, spore
and shoot systems. producing features, vascular tissue, ability
to produce seeds, and flower formation.
Plants are believed to have evolved from Among others, these features have led to
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an aquatic ancestor, which was probably classification of plants into four divisions,
Ulotrichales algae stocks. Life on land namely Bryophyta, Filicinophyta (or
started about 0.5 billion years ago when Pteridophyta), Coniferophyta (or Pinophyta)
the earliest plants started to establish their and Angiospermophyta.
life on land. The earliest plants were very
tiny and were not well differentiated into 3.6.1 Division Bryophyta
roots, stem, and leaves. In addition, they Bryophytes include mosses, horn worts and
had no vascular tissues. Water was absorbed
to their bodies by simple diffusion. They liver worts and they are the most primitive
produced motile sperms, which restricted terrestrial plants. They resemble the most
their habitats to wet areas or seasonally advanced algae species in certain ways,
wet areas. especially their dependence on water in
sexual reproduction and lack of conducting
Early plants slowly adapted to terrestrial tissues. Unlike algae, bryophytes form a
habitat by developing features such as zygote which is protected in the female
cuticle to protect them from desiccation,
development of roots and vascular system reproductive structure called archegonium
for water uptake and movement, as well that safeguards the zygote against physical
as translocation of food. Furthermore, damage and desiccation. Most bryophytes
in sexual reproduction, fertilisation was have poor vegetative differentiation
taking place inside the female reproductive because they are thallose (or thalloid).
structure called archegonia, within which The lack of conducting tissues (xylem
zygote development occurs. This was and phloem) in bryophytes, unlike in
important to protect the delicate zygote
from desiccation. The most advanced other divisions of plants, is a challenge
plants overcome dependence on water in in terrestrial environments where water
reproduction by producing special tubes is limited. However, water can simply be
called pollen tube to carry sperms to the absorbed over their surface as they have
female reproductive organs for fertilisation. various structural features to ensure the
Plants can reproduce asexually in various absorption of water falling on their surface.
ways, including the use of gemmae as For instance, their leaf-like structures are
in bryophytes, and using various other overlapping, and have small warts on them
types of vegetative reproduction, such as to delay escaping water. In addition, they
fragmentation and cuttings.
do not grow tall, hence, water can rise by
capillarity, and they also have rhizoids for
Members of the kingdom Plantae are
heterogeneous in many features. Among anchorage and ease of absorption of water
key aspects used in the classification of and mineral salts from the soil surface.

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