Describe morphological characters and adaptation features changed during evolution of nonvascular plants and seedless vascular plants.
- CHARITH AKLANSS DODANGODAGE -
If we talk a little bit about plant evolution, Fossil and biochemical evidence suggests that plants are descended from multicellular green algae. Various green algal groups have been suggested for this ancestral type, and chorophytes are often prominent. Furthermore About 700 million years ago, algae predominated in the Cambrian Oceans. About 500 to 400 million years ago, some algae migrated to land and became plants by adapting to a series of adaptations. After Vascular plants appeared by 350 million years ago, with forests soon following by 300 million years ago. Seed plants next evolved, with flowering plants appearing around 140 million years ago.
Nonvascular plants
1. Adaptation features changed during evolution
Non-vascular plants are plants that do not have a vascular system consisting of silage and phloem. Although non-vascular plants do not have these specific tissues, many have simple tissues that have specific functions to transport water internally. Non-vascular plants do not have a wide variety of specific tissue types. No cuts or stomata and no silage or phloem. As an antioxidant phylloxera, phylloxeras are unable to control water loss from tissues and are called picillohydric. Some liver warts, such as Marchantia, have incisions, while mosses have both incisions in sporophytes and stomata. They were important for the evolution of land plants.
All land plants have a generational life cycle between diploid sporophytes and haploid gametophytes, but in all non-vascular land plants the gametophyte lineage predominates. In these plants, sporophytes grow and depend on gametophytes to obtain water and minerals and to provide photosynthesis, which is a product of photosynthesis..
2. Morphological characters
Most bryophytes are small. Not only do they lack vascular tissue; They also have no real leaves, seeds or flowers. Instead of roots, they have hair-like rhizomes to anchor the ground and absorb water and minerals. Bryophytes are in moist habitats but are not as efficient at absorbing water as they are not vascular tissue. The rhizoids of bryophytes can be very fine and are only one cell long. Bryophytes also depend on moisture for reproduction. Sperm produced by female gametophytes must swim through rainwater or dew to reach an egg produced by female gametophytes. A very small generation of diploid sporophytes undergoes miosis to produce haploid spores. Moisture may be needed to disperse the spores.
The three types of modern nonvascular plants are pictured in the Figure below. Liverworts are very small non-vascular plants that have photosynthetic tissues, such as lobsters or ribbons, rather than leaves. Their rhizomes are very smooth, they have no stems and are usually less than 10 centimeters (4 inches). They often grow in ground-carpeting colonies. Hornworts are non-minute plants like liver worst. They have very delicate rhizomes and no stems. Their sporophytes are elongated and pointed like small horns. They grow several centimeters higher than the gametophytes of the plant. Moss is a large non-carrier plant with rough, multicellular rhizomes like roots. They also have very small photosynthetic structures like leaves that surround a structure like the central stem. Moss grows in clusters, which help retain moisture.
Seedless vascular plants
1. Adaptation features changed during evolution
Life Cycles with Dominant Sporophytes
the nonvascular plants, ancient relatives of vascular plants had branched sporophytes that were not dependent on gametophytes for nutrition Although these early plants were less than 20 cm tall, their branching enabled their bodies to become more complex and to have multiple sporangia. As plant bodies became more complex over time, competition for space and sunlight probably increased. As we’ll see that competition may have stimulated still more evolution in vascular plants, eventually leading to the formation of the first forests. Early vascular plants had some derived traits of today’s vascular plants, but they lacked roots and some other adaptations that evolved later. The main traits that characterize living vascular plants are life cycles with dominant sporophytes transport in vascular tissues called xylem and phloem, and well-developed roots and leaves, including spore-bearing leaves called sporophylls.
As mentioned earlier, mosses and other bryophytes have life cycles dominated by gametophytes Fossil evidence suggests that a change began to develop in some of the earliest vascular plants, whose gametophytes and sporophytes were about equal in size. Further reductions in gametophyte size occurred among extant vascular plants; in these groups, the sporophyte generation is the larger and more complex form in the alternation of generations in ferns, for example, the familiar leafy plants are the sporophytes. You would have to get down on your hands and knees and search the ground carefully to find fern gametophytes, which are tiny structures that often grow on or just below the soil surface. Transport in Xylem and Phloem Vascular plants have two types of vascular tissue: xylem and phloem. Xylem conducts most of the water and minerals. The xylem of all vascular plants includes tracheid’s, tube-shaped cells that carry water and minerals up from the roots. The water-conducting cells of the xylem are dead at functional maturity and are lignified; that is, their cell walls are strengthened by the polymer lignin. The tissue called phloem has cells arranged into tubes that distribute sugars, amino acids, and other organic products; These cells are alive at functional maturity.
Lignified vascular tissue helped enable vascular plants to grow tall. Their stems became strong enough to provide support against gravity, and they could transport water and mineral nutrients high above the ground. Tall plants could also outcompete short plants for access to the sunlight needed for photosynthesis. In addition, the spores of tall plants could disperse farther than those of short plants, enabling tall species to colonize new environments more rapidly. Overall, the ability to grow tall gave vascular plants a competitive edge over nonvascular plants, which typically are less than 5 cm in height. Over time, competition among vascular plants also would have increased, leading to selection for taller growth forms—a process that eventually gave rise to the trees that formed the first forests 385 million years ago.
Evolution of Roots
Vascular tissue also provides benefits below ground. Instead of the rhizoids seen in bryophytes, roots evolved in the sporophytes of almost all vascular plants. Roots are organs that absorb water and nutrients from the soil. Roots also anchor vascular plants to the ground, hence allowing the shoot system to grow taller. Root tissues of living plants closely resemble stem tissues of early vascular plants preserved in fossils. This suggests that roots may have evolved from the lowest belowground portions of stems in ancient vascular plants. It is unclear whether roots evolved only once in the common ancestor of all vascular plants or independently in different lineages. Although the roots of living members of these lineages of vascular plants share many similarities, fossil evidence hints at convergent evolution. The oldest fossils of lycophytes, for example, already displayed simple roots 400 million years ago, when the ancestors of ferns and seed plants still had none. Studying genes that control root development in different vascular plant species may help resolve this question.
Evolution of Leaves
Leaves are structures that serve as the primary photosynthetic organ of vascular plants. In terms of size and mega sporophylls and microsporophyll’s. Mega sporophylls have megasporangia, which produce megaspores, spores that develop into female gametophytes. Microsporophyll’s have microsporangia, which produce microspores, smaller spores that develop into male gametophytes. All seed plants and a few seedless vascular plants are heterosporous. The following diagram compares the two conditions:
2.Morphological characters
Phylum Lycopodiophyte: The club mosses, or phylum Lycopodiophyte, are the earliest group of seedless vascular plants. They dominated the landscape of the Carboniferous, growing into tall trees and forming large swamp forests. Today’s club mosses are diminutive, evergreen plants consisting of a stem (which may be branched) and microphylls (leaves with a single unbranched vein). The phylum Lycopodiophyte consists of close to 1,200 species, including the quillworts (Isotelus), the club mosses (Lycopod ales), and spike mosses (Selaginellales), none of which are true mosses or bryophytes.
Lycophytes follow the pattern of alternation of generations seen in the bryophytes, except that the sporophyte is the major stage of the life cycle. The gametophytes do not depend on the sporophyte for nutrients. Some gametophytes develop underground and form mycorrhizal associations with fungi. In club mosses, the sporophyte gives rise to sporophylls arranged in strobili, cone-like structures that give the class its name. Lycophytes can be homosporous or heterosporous.
Phylum Monilophyta: Horsetails, whisk ferns, and ferns belong to the phylum Monilophyta, with horsetails placed in the Class Equisetopsida. The single extant genus Equisetum is the survivor of a large group of plants, which produced large trees, shrubs, and vines in the swamp forests in the Carboniferous. The plants are usually found in damp environments and marshes.
The stem of a horsetail is characterized by the presence of joints or nodes, hence the old name Arthrophyta. Leaves and branches come out as whorls from the evenly-spaced joints. The needle-shaped leaves do not contribute greatly to photosynthesis, the majority of which takes place in the green stem.
Leaves of a horsetail: The whorls of green structures at the joints are actually stems. The leaves are barely noticeable as brown rings just above each joint. Horsetails were once used as scrubbing brushes and so were called scouring rushes.
Silica collects in the epidermal cells, contributing to the stiffness of horsetail plants. Underground stems known as rhizomes anchor the plants to the ground. Modern-day horsetails are homosporous and produce bisexual gametophytes.
Phylum Monilophyta: While most ferns form large leaves and branching roots, the whisk ferns, Class Psilotopsida, lack both roots and leaves, which were probably lost by reduction. Photosynthesis takes place in their green stems; small yellow knobs form at the tip of the branch stem and contain the sporangia. Whisk ferns were considered an early pterophytes. However, recent comparative DNA analysis suggests that this group may have lost both leaves and roots through evolution and is more closely related to ferns.
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