Origin Of Plants

Welcome to my blog,we are going to discuss generally on plants. Origin of plants and angiosperms,some are of the opinion that plants originate from water bodies.

They Claim that plants originated from algae which emerged from the water bodies others Believe that plants were created by God and made reference to the Bible,book of Genesis.some other authors Believe that plans evolved. The evolution concept has the following.

1. That plans appear as fossils over 400 million years ago
2. That plants evolved from green algae and invaded the vacant land. Niche
3. That many adaptations were needed as plants moved from water to land
   4.That many symbiotic relationships evolved to support plants on land
4. That early forests were dominated by giant ferns and Cycads that formed fossil fuel. These were later replaced by seed plants
5. That the first fossil vascular plants occurred at 375million years ago
6. That the fossil seed plants occurred at 360million years ago and seed plants replaced ferns and cycad.
7. Flowering plants or angiosperms evolved slowly and appeared in the fossils in 130million years ago
8. That bristle pines in the Rocky Mountains are the oldest known organisms at 4,700 years old

8. Flowering plants or angiosperms evolved slowly and appeared in the fossils in 130million years ago
9. That bristle pines in the Rocky Mountains are the oldest known organisms at 4,700 years old The origin of plants generally has been discussed. What then is the origin of the angiosperms or flowering plants. This provoked of a lot of claims some of which are stated below

The origin and development of the angiosperms
The angiosperms are known to be widely distributed and cover a greater parts of the earth surface than any other taxa. There are usually two types of angiosperms,the dicotyledon and monocotyledons. The evolution of the angiosperms attracted the attention of many scientific workers. This resulted in many theories propounded to explain the origin and development of the angiosperms. Some of the theories are

1. Bennetitales and Ranales theory where the various views of Hallier (1960 Arber and Parkin,1907 and hunchison 1925) were expressed
2. Coniferae and Amentiferae theory
3. Gnetale,casuarinales theory
   4.. Caytoniales ,Angiosperms theory

Bennetiatales Ranales Theory
In this theory,Hallier’s view was that the group of plants called Bennetiatales may have been the derivative of another group called cycadeoidea and that monocotyledons dicotyledons. He further said that another group called Ranales with their male and female sporophyll and the one of cycadiodea are definitely alike.

However the evidence from the differences in anatomical structures of wood in the two groups Bennetiatales and Ranales led to differences in accepting Hallier’s view Arber and Parkin (1907) accepted Hallier’s views but presented another explanation based on imaginery group of plants. Which they called Hemiagiospermae.

They reported that this group of plants have the cycodiodea flowers this linking the imaginary group of plants with Bennetitales and Ranales. They further upheld that from the Hemiangiospermae group the Ranalian type of flowers may have origihated and that all other groups of the angiosperm arose from the Ranalian group of plants. They held the view that the earliest monocotyledons were more primitive than the dicotyledons.

Anatomical evidence from the wood did not support their views and therefore they had no I usis for their views. Hunchinson (1925) endorsed the views of Hallier, Arber and Parkin. He based his views on two parallel evolutionary lines.

Coniferea Amentiferae theory
Engler and Partle (1924) rejected the views of Hallier I.e the cycadeaoideab origin of the angiosperms. They held the view that dicotyledons and monocotyledons had arisen independently from hypothetical groups of plants which they claimed to the extinct gymnosperns .

They said these are extinct plants were similar to coniferae with uni flowers which developed were similar to coniferae with uni flowers which developed in the Mesozoic period. They considered the monocotyledons more primitive than the dicotyledons.

Gnetales Casuarines Theory
Westein (1935) held a divergent view from that of others. He said the angiosperms of the casuarina type originated from Gnetales especially the Ephedra which is highly advanced Angiosperms.

Lower Plants or Seedless plants or Non flowering plants

Lower plants can be called seedless plants or non flowering plants. The word lower does not mean that the plants are low to the ground. This simply means that the plants compared to seeds do not produce seeds and do not have high efficient conducting or vascular bundles. Although there are vascular seedless plants . Some of the lower plants are ferns, bryophytes, fungi, etc there are vascular and non vascular lower plants. The study of fungi is presented In the section of mycology. The non vascular and vascular seedless plants are discussed in this section.

The non vascular seedless plants
The non vascular seedless plants which are mainly the bryophytes have three phyla . These include

1. Phylum Hepatophyta – liver worts which are about 9,000 species
2. Phylum anthocerophyta – Hornworts which is made up of about 100 species

3: phylum Bryophytes – mosses which is made up of about 15,000 species.

The Vascular seedless plants
There are two phyla in the vascular seedless plants . There are the life cycle of Fern- seedless plant.

phylum Lycophyta i.e. the lycophytes made of 1,200 species
and Pterophta ie the pterophytes made up of 12,000 species.
Campbell et al., (2008).

Non vascular plants are generally referred to as Bryophytes. This
is derived from the Greek word bryon which means moss and
phyton which means plant. The non vascular plants of present
day are herbaceous i.e. non woody plants e.g. mosses.The life cycles of two examples are shown in Plate 3. Plate 3 is the life cycle of a fern as reported by Campbell Et al. (2008).

The fern life cycle as illustrated in plate 3 is such that the adult
plant is the sporophyte.
On back side of the sporophyte
repeoductive leaves are cluster of spots called Sori (plural) and
sorus singular. A sorus is actually a body called sporangia. A
sporangium contains the reproductive spores. The spores
undergo meiosis. There after the spores are released and
dispersed. The spores in some cases are single celled spores
which develop into photosynthetic gametophyte

The young growing spore i.e. young gametophyte grows into a
mature ametophtyte which bears the male reproductive units i.e.
Antheridium which is the sperm and the female reproductive
part which is egg.
The male and female reproductive units produced fuss fcr h/. it
ion. When this happens a zygote is formed. This zygote matures
to form a new sporophyte. The plant continues with this process
of reproduction to sustain its kind. The process discussed above is the reproduction of Fern.

Vegetative Reproduction
Bryophytes can reproduce along the ridges of the Sporophyte are cup like structures called Gema( singular), germae (plural) cups. These cups when matured detract from the parent plant and establish as new plants. The rhizomes which are root like structures anchor the plants to the ground and absorb the needed nutrients and water for the plant. The rhizoid also provide habitat for blue green algae which are helpful in the fixation of atmospheric nitrogen. The diversity and some related concepts are discussed.

Economic importance of Bryophytes

Bryophytes play a role in Agriculture, the thallus body provides habitats for blue algea. These organisms fix atmospheric nitrogen, Nitrogen improves soil fertility. As bryophytes grow in dense mats on surface of the soil, they prevent soil erosion by running water and rain droplets. As they die and decay they add value to the humus component of the top soil.