Question

Plant Evolution. As far as we know, land plants evolved only once, and therefore all land plants alive today share a common ancestor from which the various plant lineages have evolved.

(A) From which taxonomic group of organisms (please be specific) did all land plants evolve, and approximately when did this occur? In what sort of habitat did these organisms live and how might this have helped facilitate their transition to land? What adaptations did the first land plants have that set them apart from their ancestors and allow them to move out of aquatic environments and into terrestrial environments? Which extant (still living) group of plants is probably most similar to those first land plants?
-

(B) Now consider the five major taxonomic groups of plants we discussed in class (bryophytes, lycophytes, pteridophytes, gymnosperms, and angiosperms). For the last three groups (pteridophytes, gymnosperms, and angiosperms), give the approximate time when each group first evolved and briefly describe the key adaptations that set each of them apart from other plant taxa. Describe how these adaptations helped individuals be successful, given the environmental conditions in which they evolved.
-

Answer 1

We have already spent a lot of time considering the life growth tree and the three domains of life. We now confine ourselves to a specific lineage in the Eukaryote, which is present in Eukarya: land plants. Note that during this reading we are specifically referring to earth plants such as moss, ferns, conifers and flowering plants. Water, photosynthesis, and eukaryote algae are also commonly regarded as plants (although not clearly ground plants); However, the term "algae" refers to a large and diverse photosynthesis group consisting of green, brown and red algae, which do not have the same common photosynthetic ancestors (in other words, the term "algae" is not monophonic). But green algae and land plants share a common photosynthetic precursor: earth plants originate from the green algae cluster of 480–470 MOAs during the Pheonzoic period.

The ancestor of all terrestrial plants is aquatic, green algal-like species. Living in the water offers many advantages over life on earth:

In or near water, plants can meet the need for a certain absorbent organ or tissue to absorb water around them to prevent indigestion (drying out).
Water provides external structure and light to organisms; Additional structural support is needed to keep people from living on land.
Sperm and egg can easily find each other by swimming in an aquatic environment, and they do not need protection from dehydration. Sperm and eggs need alternate strategies to a) find each other and b) avoid drying out when grinding.
Water filters ultraviolet-B (UVB) light, which is devastating to DNA. No such filtration occurs in the air, so terrestrial organisms need alternative strategies to protect them from UV radiation.
If life on Earth presents so many challenges, why would any earth plant grow to survive on Earth? Life on earth provides many benefits - especially during the 470 MEA Ordovician period:

Sunlight is more abundant in the air than water. Photosynthesis is a water filter that changes the spectral quality of light absorbed by chlorophyll.
Carbon dioxide is easier to get into the air than water because it diffuses rapidly into the air.
Land plants have evolved before land animals; Therefore, none of the predators endangered early life. This situation has led to the colonization of animals, where they feed on the abundance of nutrients in established flora. As a result of this selective pressure on herbivores, plants have developed adaptations to prevent predators such as vertebrates, thorns and toxic chemicals.
Switching from aquatic to terrestrial climate has given rise to many specific adaptations to the above challenges for survival on Earth. In fact, modern land plants have a range of adaptations to life on earth, but they have not evolved all at once. In addition, different plant lineages have different adaptations. Adaptations and characteristics of (almost) all land plants:

Wax cuticle covering the outer surface of the plant and preventing it from drying out by evaporation. Cutical UV protects partially from radiation damage from light.
All land plant clans, except liverworts, have stomata (singular: stomata) (-likely -! - moss). Stomata are holes or holes that allow the exchange of gases (such as oxygen and carbon dioxide) between plant cells and the environment. Earth plants require stomata or similar structures because the wax prevents the free flow of cuticular gases.
The roots (or root-like structures) in the soil act as anchor plants and - in plants with real roots - as a drain for water absorption. All terrestrial plants have real origins except bryophytes (mosses, liverworts and hornworts). Bryophytes have root-like structures called rhizoids, which anchor them to their surface, but are not involved in water absorption (bryophytes are less important because they can survive only in humid climates).
Interactions with mucosal fungi that are tightly linked to plant roots. Mycorrhizal fungi are associated with up to 80% of all land plants and provide additional surface area to absorb both water and nutrients from the soil. The fungus shares these resources with the roots of the plant, and shares the plant-photosynthetic sugar products with the fungus.
Selection of generational life cycle including multi-cellular haploid phase and multi-cellular diploid phase. Why is this an adaptation to life on earth? In fact, it also occurs in * some * green algae, which are aquatic, but all share a common ancestor with earth plants. But for generations they have specific adaptations to life cycle choices

Early land plants cannot escape the abundant water resources. During development, land plants have developed strategies for increasing dryness:

Non-vascular plants, or bryophytes (liverworts, moss and hornworts), in many ways, are physically bound to water. Their main adaptations to life on earth include wax cuticle and root-like structures (rhizomes). Unlike those two features, they are very dependent on water for their life cycle: they must live in a very humid environment near water sources. They are so low that there is no water carrying mechanism against gravity. Their sperm and eggs need water for intercourse: gametes are not protected from constipation, and must swim in clear sperm water to find the egg.
Compared with nonvascular plants, seed vascular plants (lycophytes, ferns and horserails) have two main adaptations: true roots and vascular tissue. These adaptations have allowed seed-free vascular plants to outperform non-vascular plants during the early colonization of life on earth.
True roots grow deeper in the soil than rhizoids, which allows water and nutrients to be extracted from the soil better.
Vascular tissue (xylem and phloem) consists of tubule-like cells that allow the transport of water (in the xylem) from the roots to the leaves and the sugars (phloem) from the leaves. Adaptation to vascular tissue means that these plants grow taller than bryophytes (and therefore have greater access to sunlight for photosynthesis).
In addition to these two adaptations, seed-free vascular plants still adhere to water for reproduction: like bryophytes, their sperm and eggs are sensitive to dehydration and the sperm must swim through the water to get to the egg.
Seed, flowering plants, or gymnosperms, (ginkgoes, cycads and conifers) have three additional adaptations beyond seedless vascular plants, which enable colonization of dry habitats rather than nonvascular and seedless vascular plants.
Lignin is the optical component of some plant cell walls, which provides structural rigidity and allows the movement of water against gravity, resulting in plant growth.
Pollen, the mechanism of transport of sperm to the egg when there is no water. Many sources suggest that pollen is very similar to sperm, which is not true. In fact, pollen produces sperm. In the meantime we will revisit this course, so for the time being, pollen protects the sperm from dehydration and provides a way to reach the sperm egg when there is no water. Seed flowering plants rely on air to transport egg pollen (hence sperm).
The seeds protect the earth from fertilizing eggs in many ways. Clearly, the seed is a rigid anatomical structure that protects the fertilized egg (embryo). A form of 'suspended animation' for seed embryos, which inhibits growth until the environmental conditions are conducive to seed germination (the emergence of the embryo from the seed of the plant. When it begins to grow).
Flowering plants, or angiosperms, have a recent adaptation to life on earth: flowers, double fertilization, and endosperm and fruits:
Flowers may not seem like an obvious adaptation to live on Earth, but flowers rely on eggs (and therefore sperm) to move insects on pollinators (such as insects, birds, bats and other animals). Dependence on pollinators is far less random than dependence on air, which represents an important adaptation to life on Earth - as well as co-evolution with specific pollinators.
Double fertilization and endosperm: Double-fertilization is a unique process in flowering plants, where one sperm forms an egg into an embryo, and another sperm fertilizes another structure next to the egg to form an endosperm. Endosperm undergoes a kind of pseudo-development where it grows in mass and provides nutrients to the developing fetus during geo