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Rhyniophyte Flora vascular plant age determination

Question 1.

The first flora, known as the “Rhyniophyte Flora”, was found under the early Devonian Era, a geologic time, approximately 400 million years ago. The first flora leads us to a rich fossil land in a village called Rhynie in Aberdeenshire, Scotland.  This vascular plant age determination is based upon two factors; radiometric dating and biostratigraphy. Radiometric dating is a technique used to date geological materials by measuring the quantity of radioactive and naturally occurring isotope and its decay products, by the rate of the decay. Biostratigraphy is based on using the fossils within the plant to determine the age. The rhyniophyte floras were leafless as well as seedless; however it was the first vascular plant. It was also a polysporangiophytes because their sporophytes contained branched stems which carry sporangia, the enclosed space where the spores are formed. They were also homosporous, producing spores of the same size. It consists of dichotomous branching, meaning that the apical meristem divide at different intervals, into two parts. The plants that classifies as the first floras are rhyniophyte, zosterophyllophyte, and trimerophyte. Rhynia is perhaps the most dominant plant in the category of first flora. Rhynia was inhabitant of swamps, and grew from branched rhizome. The plant had many lateral branches and stomata, which means it was photosynthetic, there were small tips on the stems that were missing vascular tissue. In its interior was a protostele, creating the solid core of xylem enclosed by the phloem. However, all three groups became extinct in the end of the Devonian era, approximately 360 million years ago. The rhyniophyte has most likely not given rise to any modern plants, but the zosterophyllophyte and trimerophyte may have given rise to lycophytes and pterophytes, respectively.

The second flora, the coal age flora, arises during the Carboniferous period, approximately 360 to 290 million years ago. This era was characterized by tropical temperatures, with growing circumstances favorable all year around. The lands were low and covered by shallow swamps and water. There were five types of plants that dominated the land during the Carboniferous period; it was the three vascular, seedless plants - lycophytes, ferns, and equisetophytes (calamites), and the two other were gymnospermous seed plants - seed ferns and cordaites. Most dominant plants of the coal-forming swamps of the period were the tree lycophytes. These trees could be from 10-35 meters, and were branched sparingly. Similar to the first flora, it also branched dichotomously. It had long microphylls, similar to veins or leaves. The lycophyte trees were heterosporous in contrast to the rhyniphyte, however the tree became extinct by the end of the Carbonferious period probably as a result of the changes in the climate, decreased temperature, and the swamps drying up. There was one surviving group of carbonerious gymnosperms, the conifers.

Question 2.

The Gymnosperm Flora, also known as the third land flora, was one of the most important evolutions of the vascular plants. The initial evidence of gymnosperms emerged in the Paleozoic era and became the most vital global plant during most of the Mesozoic era and up until about 100 million years ago. The Mesozoic period includes the Triassic, the Jurassic, and the Cretaceous periods. Gymnosperm are primitive seed plants, the word also means a naked seed. The gymnosperms are wind pollinated, and exposed instead of being covered. Apparently, the progymnosperms fossils gave life to the gymnosperms and the seed plants; the progymnosperms has the characteristics of a combination of seedless vascular trimerophytes and seed plants. The seeds characteristics consist of embryo, stored food, and a seed coat covered with inguments. There are four phyla commonly referred to gymnosperms; Cycadophyta, Ginkgophyta, Coniferophyta, and the Gnetophyta. The most important gymnosperm phyla existing and living today is the coniferophyta, which consists of 70 genera and approximately 600 species. It is also known as the tallest vascular plant on the westcoast, known as redwood trees which can grow up to 113 meters. Conifers also include pines, firs and spruces.

Pines are a type of conifer with a special leaf arrangement. Most people are familiar with pine cones, making it probably the most well known gymnosperm. Pines are spread out stretching from North America and Eurasia, as well as broadly cultivated in the Southern Hemisphere. There are 90 different species of pines, and they are differentiated by the arrangement of the leaves. Pine develops into producing leaves in fascicles after a year or two of growth, each of fascicles consists of a particular amount of needles, depending on the sort it could be from one to eight. The fascicles are essentially short shoots as a result of inactive apical meristem. The pines are exceptionally suited for development in environments with lack of water. Within the pines are thick cuticles that wrap the epidermis, underneath it there are a couple of layers of hypodermis. The stoma is hidden below the facade of the leaf. The majority of pine species preserve their needles for 2-4 years, and the photosynthetic stability is dependent on the physical condition of numerous years' harvest of needles. However, the needles of the longest lived tree, the bristlecone pine, can be maintained up to 45 years and stay photosynthetically dynamic the whole time.  It is important to note that the life cycle of a pine is approximately over a two year period. 

There are also two types of extinct gymnosperms, the seed ferns as well as the Cordaitales. The seed ferns were very assorted and abnormal; they varied in the shapes from lean, branched plants to plants that looked like tree ferns. The other group is the cycadeoids, which is plants with leaves similar to palm leaves, and also similar to the existing cycads. Cycadeoids, also called Bennettitales, are a mysterious group of Mesozoic gymnosperms that vanished during the Cretaceous era from the fossil record. Bennettitales separated itself from the cycads in numerous ways, along with the existence of flowerlike reproductive composition that were bisexual in several types.

Question 3.

Angiosperm is if the fourth land flora, but also the flowering plant. It is basically everything you see in the modern plants, from trees, fields, lawns, wildflowers to fruits. Angiosperms are extremely vast and diverse; they are a product of phylum anthophyta that includes up till 300,000-450,000 species, and by far the biggest photosynthetic phylum. They range greatly in size, from floating plants that are barely 1 millimeter long to Eucalyptus trees over 100 meters tall. Angiosperms are traced back to the Cretaceous period, during the Mesozoic era. The phylum spread widely all around the world within the first 30-40 million years and has since then dominated the land. Angiosperms have many common distinctive features making it clear that they are a consequent of a single common ancestor, monophyletic. Angiosperms are different from other seed plants in some special distinctiveness, like the existence of endosperm in the seeds. Additional characteristics of angiosperms are double fertilization resulting in endosperm development, existence of sieve tubes and companion cells in the phloem, as well as closed carpels.

There are two classes of angiosperms, the monocots and the eudicots. There are two different ways as of how the plant obtains nutrition, both parasitic and saprophytic. Parasitic plants shape dedicated absorptive organs, called haustoria, which enter the tissues of their hosts; in contrast, saprophytes get their food from decomposing organic substance. The pollination within this flowering plant begins by the transfer of pollen grains from the anther to the stigma. During dispersal, the pollen grain is an undeveloped male gametophyte, and it possibly encloses two or three cells. Primarily, there is a generative cell and a tube cell, essentially separating before or after spreading leading to two sperm; this along with the sprouted pollen grain is the full-grown microgametophyte. The evolution of this plant is closely related to its insect pollinators, especially beetles. The flower plant would not develop without the help of the insects. Angiosperms attract both insects and animals with their flowers, causing a cross-pollination that occurs frequently. Pollination by animals and insects are much more efficient than wind pollination, which is probably the main reason why the angiosperms have grown so dominant. Which insect that are pollinating the plant depends on the flowery scent, whether it is fruity or bear a resemblance of manure or carrion, and in flower-pollination by beetles the flowery pieces are regularly covered and as a result sheltered from the nibbling visitors. An important type of angiosperm worth mentioning would be the Archaefructus, which is the earliest angiosperm we can learn anything from. Apparently, this sort was in recent times discovered in China, it was documented as an angiosperm due to the fact that the carpels and fruits had seed enclosed. Other characteristics would be the simple roots, herbaceous stalks, leaves that were cut apart, and stamens.

Question 4.

Haplodiplontic is the major characteristic in the typical ferns life cycle. Mature ferns have fonds or leaves that are covered in sporophytes underside of their leaves, which produce and release spores. By meiosis, spores are produced in the sporangia and then cast onto the ground to grow on there own. Each spore germinates by itself and becomes a gametophyte. In the lower surface, mature gametophyte makes immature antheridium which produces a sperm, and immature archegonium which produces a egg. When enough moister occurs along with a mature sperm, the antheridium releases the sperm, which swims into archegonium where the sperm and the egg fertilize. When fertilization occurs, the zygote begins to divide almost immediately, to become a young embryo. The embryo develops and differentiates into the mature sporophyte, which obtains nutrition's through photosynthesis as it houses non internaly. Once the young sporophyte sprouts in the soil, the gametophyte collapses and a new fern is now created.

Conifers have two kinds of augmented branch, one with male pollen-bearing cones strobili and one with ovulate cones or seed cones. Each scale of the stobili bears a microsporangium that then generates microspore mother cells. Through the process of meiosis, microspore mother cells produce large amounts of microspores that then develop into pollen grains that are produced by prothallial cells and generative cells. Pollen grains or male gametophyte germinate to create sperm. Seed cone has two denuded ovules in ovuliferous scales. Megaspore mother cells in the ovule then divided into 4 megaspores through meiosis. The megaspore developes as the others degenerate and becomes archegonia with two egg cells. Tthe pollen grains are then transferred by wind to the female gametophyte in the ovule through a opening in the integument. The sperms swims into pollen tube that is created during fertalization and reaches to the egg, once there one degenerates. After fertilization, the ovule matures and turns into the seed with a seed coat. The embryo grows, and the suspensor which interconnects the endosperm to the embryo falls apart. Made up of an embryo, seed coat, and nutrients, the conifer seed is completed. And falls to the grownd to spout and become a new plant.

The major parallels of ferns and conifers is that they both experience fertilization and meiosis. The major differentiations are that conifers are heterosporous, while ferns are homosporous, as well as the fact that conifers have the gametophyte in life cycle while ferns have the sporophyte that become gametophyte on their own.

The significant asset of life cycle with seeds is that pollen needs no special condition to reach the egg since insects, animals or weather (natural pollinators) can help pollination, while seedless plants need moist condition since they are unable to fertilize in dry area. The significant asset of life cycle without seeds is that they can reproduce by themselves, not depending on others. Plants with seeds cannot fertilize if there is a shortage of pollinators.

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