This analysis supports the hypothesis that the land plants are placed phylogenetically within the Charophyta, identifies the Charales (stoneworts) as the closest living relatives of plants, and shows the Coleochaetales as sister to this Charales/land plant assemblage.
The charophyte green algae (CGA) are thought to be the closest living relatives to the land plants, and ancestral CGA were unique in giving rise to the land plant lineage. The cell wall has been suggested to be a defining structure that enabled the green algal ancestor to colonize land.
The adaptations and characteristics which ARE present in (nearly) all land plants include: A waxy cuticle that covers the outer surface of the plant and prevents drying out through evaporation. The cuticle also partially protects against radiation damage from UV light.
The key difference between Chlorophyta and Charophyta is that Chlorophyta is a taxonomic group of green algae living predominantly in marine water while Charophyta is a taxonomic group of green algae thriving mainly in freshwater.
The charophytes have DNA that is closer to land plants than other green algae. Together, these observations provide good evidence that land plants and charophytes shared a common ancestor.
Why are algae considered plant-like? The main reason is that they contain chloroplasts and produce food through photosynthesis. However, they lack many other structures of true plants. For example, algae do not have roots, stems, or leaves.
?They are considered to be an ancestral to plants because both they both reproduce chlorophyll a/b, both have cell walls made od cellulose. But, land plants are multicellular, autotrophic and have a nucleus, most green algae are same but otherare not.
Algal groups; water plant; earliest ancestors of land plants. Why are Charophyceans thought to be ancestors of land plants? One population of charophycean ancestors enabled their descendants, the first land plants, to live permanently above the waterline.
In addition to vascular tissues, these early plants evolved other adaptations to life on land, including lignin, leaves, roots, and a change in their life cycle. Lignin is a tough carbohydrate molecule that is hydrophobic (“water fearing”).
Kingdom Fungi, one of the oldest and largest groups of living organisms, is a monophyletic group, meaning that all modern fungi can be traced back to a single ancestral organism. This ancestral organism diverged from a common ancestor with the animals about 800 million to 900 million years ago.
It was previously thought that land plants evolved from stonewort-like algae. However, new research published in BioMed Central's open access journal BMC Evolutionary Biology shows that the closest relatives to land plants are actually conjugating green algae such as Spirogyra.
By examining the four major groups of living plants, you will be able to review the adaptations that enabled the first non-vascular and vascular plants to survive on land. These are the mosses (non-vascular plants), the ferns (seedless, vascular plants), gymnosperms and angiosperms.
Formerly algae were considered part of the kingdom Plantae mainly because of their photosynthetic competency (autotrophy), but today many classification biologists place algae in the kingdom Protista, a kingdom comprising mostly unicellular eukaryotic organisms.
Protists are a diverse collection of organisms. While exceptions exist, they are primarily microscopic and unicellular, or made up of a single cell. At one time, simple organisms such as amoebas and single-celled algae were classified together in a single taxonomic category: the kingdom Protista.
As already noted, a shared feature of all land plants is the presence of a multicellular diploid stage, the sporophyte, which is produced in alternation with a haploid multicellular stage, the gametophyte. These two stages comprise the “alternation of generations” life cycle (Haig and Wilczek, 2006).
Protists are diverse and do not have one exclusive common ancestor. This is an informal term that is no longer representative of current scientific knowledge. A clade is a group of organisms that we believe evolved from a common ancestor, thus protists do not fit into one single clade.
All algae use chlorophyll a to collect photosynthetically active light. Green algae and euglenophytes also use chlorophyll b.
The Protista, or Protoctista, are a kingdom of simple eukaryotic organisms, usually composed of a single cell or a colony of similar cells. Protists live in water, in moist terrestrial habitats, and as parasites and other symbionts in the bodies of multicellular eukaroytes.
They are basically unicellular but oomycetes (Oomycota) are composed of multinuclear mycelia and brown algae (Heterokontophyta) form large multicellular thalli with differenciated tissues.
a. Protists are more closely related to animals. Both protists and animals fall under the category of eukarya and bacteria is a separate category. Some of the protists observed fell under the category of ciliates, which the branch in the phylogeny tree is the closest branch to animals.
The five traits are:
- Apical meristems.
- Alternation of generations.
- Multicellular embryo that is dependent on the parent plant.
- Sporangia that produce walled spores.
- Gametangia that produce gametes.
Summary
- Plants are multicellular eukaryotes. They have organelles called chloroplasts and cell walls made of cellulose.
- Plants also have specialized reproductive organs.
- Almost all plants make food by photosynthesis.
- Life as we know it would not be possible without plants.
A terrestrial plant is a plant that grows on, in, or from land. Other types of plants are aquatic (living in water), epiphytic (living on trees) and lithophytic (living in or on rocks).
In land plants, a waxy, waterproof cover called a cuticle protects the leaves and stems from desiccation. However, the cuticle also prevents intake of carbon dioxide needed for the synthesis of carbohydrates through photosynthesis.
Plant adaptations to life on land include the development of many structures — a water-repellent cuticle, stomata to regulate water evaporation, specialized cells to provide rigid support against gravity, specialized structures to collect sunlight, alternation of haploid and diploid generations, sexual organs, a
There are
two main
types of plant defenses: constitutive and induced.
Interesting Facts about Plant Defenses
- Many drugs we use today are made from chemicals that plants use to protect themselves.
- Some plants provide housing for animals that prey on herbivores that may eat the plant.
The
spores can be of two types: homosporous and heterosporous.
Spores:
| Seeds | Spores |
|---|
| Seeds are mostly present inside a fruit. | Spores are found underside the leaves of ferns and mosses and gills of the fungi. |
| They are macroscopic. | They are microscopic. |
| Seeds are produced in fewer numbers. | Spores are produced in large numbers. |
Embryophytes are complex multicellular eukaryotes with specialized reproductive organs. The name derives from their innovative characteristic of nurturing the young embryo sporophyte during the early stages of its multicellular development within the tissues of the parent gametophyte.
Four key traits appear in nearly all land plants but are absent in the charophytes:
- Alternation of generations (with multicellular, dependent embryos)
- Walled spores produced in sporangia.
- Multicellular gametangia.
- Apical meristems.
