Kingdom Plantae, otherwise known as the plant kingdom, consists of every plant in the world – including multicellular, eukaryotic, and autotrophic organisms.
For an organism to be considered part of the Kingdom Plantae, it must be able to photosynthesize, therefore it requires chloroplast and chlorophyll pigment.
In its history, Kingdom Plantae once consisted of all living organisms, including fungi and algae, but the current definition now excludes these organisms.
With approximately 320,000 species of recognized plants, Kingdom Plantae is one of the largest Kingdoms on the planet.
Kingdom Plantae Characteristics
There are several key characteristics of the plant kingdom, including:
- Organisms can reproduce sexually or asexually by propagation.
- Organisms are multicellular eukaryotes, with the cell containing a large central vacuole and an outer cell wall.
- Organisms are non-motile.
- Organisms are autotrophs, meaning they make their own food.
- Organisms have separate organelles for photosynthesis, reproduction, support, and anchorage.
- Organisms contain chlorophyll in the plastids, which are pigments responsible for photosynthesis.
- Plants have two main organ systems, including the root system and shoot system. The root system consists of the roots, tubers, and rhizomes, and the shoot system consists of the flowers, leaves, stems, and buds.
However, members of the plant kingdom don’t necessarily have to meet all of these characteristics to be considered part of the kingdom.
For example, some plants (like the Indian pipe plant, otherwise known as Monotropa uniforma) don’t have chlorophyll, and instead obtain nutrition from decaying plant matter or other plants.
They are known as holoparasites. Other parasitic plants can photosynthesize to some level, and they are called hemiparasites.
Kingdom Plantae Classification
The general classification of Kingdom Plantae is that the Kingdom is filled with every plant organism on the planet. It has been classified into subgroups according to the vascular system, plant body, and seed development.
These subgroups include Angiosperms, Gymnosperms, Marchantiophyta, Bryophyta, Anthocerotophyta, and Pteridophyta.
As the subgroups rank above classification, considering they are more specific than class, these subgroups are part of the phylum category.
Kingdom Plantae Phylum
Angiosperms – Phylum Magnoliophyta/Anthophyta
Members of the Angiosperms Phylum are also known as flowering plants, making up for the most common plants in the world.
In fact, over 80% of the plants on Earth are members of this Phylum.
These species can be found on every continent and every habitat except from the Antarctic.
As Angiosperms produce flowers that contain pollen, the members of this Phylum are considered the most evolved plant species.
Not only does the pollen help to keep the Phylum so large, but the species can also produce fruits with seeds, which subsequently leads to frequent pollination and propagation.
It is believed that the Angiosperms Phylum consists of over 300,000 species, making it the largest Phylum in Kingdom Plantae.
There are two main groups of Angiosperms, which are divided based on their characteristics. These include Monocots and Dicots.
Monocots are a group of Angiosperms that contain a single embryonic leaf in the seeding, also known as cotyledon.
In most Monocot species, the stem is unbranched and often contains nodes. They typically have adventitious roots, meaning the roots grow as a result of external factors.
Other characteristics of Monocots include scattered vascular tissue, and the veins of the leaves generally run parallel to the length.
Here are some plants in the Monocot category:
- Sugar cane
Unlike Monocots, Dicots feature two cotyledons or embryonic leaves. Traditional flowers are typically classified in this category of Angiosperms.
These organisms feature leaves with networks of veins and a tap root. Plus, the vascular tissue is arranged in a ring-like form within the stem.
Here are some examples of Dicots:
Aside from Monocots and Dicots, the Angiosperm Phylum also consists of another group of plants known as Basal Angiosperms.
These organisms share qualities and characteristics of both Monocot and Dicot organisms.
There are approximately 9,000 species of Basal Angiosperms, which are then further separated into two categories: the Magnoliids and the ANITA Basal Angiosperms.
The vast majority of Basal Angiosperms belong to the Magnoliids category.
Some examples of Basal Angiosperms include:
- Avocado trees
- Japanese star anise
Despite the category the organisms belong in, each member of the Angiosperm Phylum shares some general morphological characteristics.
First and foremost, all Angiosperms are flowering plants, which is the key defining characteristic.
Secondly, every organism in this Phylum consists of a stem, leaves, and seeds – all of which can be of varying shapes, sizes, and arrangements.
Other important features include the sepal, stamen, petals, and carpel.
As with another Phylum called Gymnosperms, the pollen and ovules of Angiosperms are found in the flowers while the seeds are inside the fruits.
Interestingly, the reproductive organs of Angiosperms are found in the flowers.
The stamen is the male sex organ, and is made up of an anther (where the pollen grains are located) and filament. The carpel, also known as the pistil, is the female sex organ that contains the ovules.
When the pollen is dispersed from the anthers, the pollen (each pollen consisting of a tube cell and generative cell) falls on the stigma.
Here, the germination process begins, where the pollen grows tubes down to the ovule in the carpel.
The male gametes fuse with the female egg, resulting in a zygote.
This zygote forms into an embryo whilst the ovules develop into seeds. As this happens, the ovary becomes a fruit which then contains the seeds.
During this fertilization process, the triploid primary endosperm nucleus (PEN) is produced when the male gametes fuse together with the diploid secondary nucleus.
When the PEN develops, the endosperm then helps to nourish the developing embryo.
Gymnosperms – Phylum Coniferophyta
Gymnosperms are commonly known for their naked seeds, meaning the seeds are not located inside a fruit. Instead, the seeds are seen by the naked eye.
This clue is actually obvious in the name of the Phylum, as Gymnosperms derives from the Greek words “Gyros” (meaning naked) and “Sperma” (meaning seeds).
Members of the Gymnosperms Phylum are believed to be the first seed-producing vascular plants.
Most of the species in this Phylum are woody plants, with a few shrub species, found in the Northern Hemisphere.
They typically grow in cool temperate and boreal areas, like the Taiga forests in subarctic regions.
Also hinted by the name “Coniferophyta”, this Phylum predominantly consists of members of the conifer family.
Here are some examples of Gymnosperm species:
- Abies grandis (Grand fir)
- Larix kaempferi (Japanese Larch)
- Taxus baccata (The European Yew)
- Araucaria columnaris (Cook pine)
- Abies lasiocarpa (Subalpine fir)
Conifers are known for being some of the tallest trees on the planet, such as the Giant Sequoia tree (one of the three redwood tree species). The species in this phylum are characterized by roots, branches, leaves, and a stem.
Interestingly, the leaves of Gymnosperm species aren’t like traditional leaves.
They are also known as needles or scales due to their small and pointy structure, which varies depending on the species.
For example, the Giant Sequoia features tightly-packed, short leaves, and the Yew has long linear leaves with pointed tips.
The majority of conifers are evergreen, meaning they remain green throughout the year, though there are some exceptions to this characteristic – for example, the Larch is a deciduous conifer that belongs in the Phylum.
While evergreen leaves gradually shed their leaves throughout the year to make room for new ones, deciduous trees like Larch trees shed their yellowing leaves in winter, leaving the tree completely bare of leaves.
Interestingly, some species – like Pine trees – feature leaves that are covered by a waxy-like material.
This helps to retain the water throughout the winter, which is also why Pine trees stay notoriously green throughout the cold months.
The stem of the Gymnosperm species is anchored into the ground thanks to tap roots.
These tap roots are responsible for garnering water and nutrients in the soil, which are then transported evenly to the whole plant through the vascular tissue.
The roots can be associated with bacteria or fungus, depending on the species.
For example, the fungus mycorrhiza is found in the Pinus tree roots, while Cycas trees contain nitrogen-fixing bacteria in their roots.
It’s worth noting that Gymnosperms do not produce fruits and flowers. Instead, they rely on their cones for reproduction.
Most conifer species are monoecious, meaning the male and female cones (seeds) often reside on the same plant, meaning the species are hermaphrodites.
The female sex organ is known as the inflorescence, which is a series of overlapping, soft scales that are brightly colored and form the strobilus, or the immature corn.
The ovules are contained in the strobilus, but they aren’t contained in an ovary.
The male cone is typically smaller than the female cone, and as with the Angiosperm species, carries the powdery pollen. This pollen is usually transported by wind and movement in the tree.
When the female cone has been fertilized by the pollen, it develops into a mature cone complete with seeds. The cone then opens and disperses those seeds, forming more trees when the seeds reach the ground.
The Phylum Bryophyta consists of plants known as mosses, which is evident thanks to its name – with “Bryon” meaning moss and “Phyton” meaning plants in Greek.
In the earliest days of this Phylum, hornworts and liverworts were also included in this division.
Bryophytes (the members of the Phylum) are some of the most primitive plant species in the world, commonly found in favorable survival conditions, including shaded and moist areas.
This Phylum consists of roughly over 12,000 species.
Some of these species include:
- Sphagnum species
- Funaria species
- Polytrichum species
The main physical characteristics of Bryophytes include the stem and leaf structures, as well as the rhizoid (multicellular) structure.
The leaves are distributed in a spiral position and originated from divisions of the apical cell, producing a mass of small, tightly-packed leaves that are synonymous with moss.
There are two main groups that are defined by the characteristics of leafy shoots in Peristomates – acrocarps and pleurocarps.
Mosses with acrocarps have a characteristic erect shoot system that often branches, whereas pleurocarps have a creeping shoot system with lateral branching.
Moss leaves are generally ovate or lanceolate in shape, and they are mostly undivided. The tiny branches found in moss develop from superficial buds.
The stem structure of mosses is complex, consisting of hydroids (cells that are responsible for water conduction), the epidermal layer, and a cortex.
The cells in the epidermal layer have a thick pigmented wall, small Lumina, and they are elongated. The cells are responsible for producing a waxy texture, which helps to retain moisture.
The cortex is made up of two zones – the scleroderma and the inner cylinder.
The scleroderma is the outer zone responsible for providing mechanical support, while the inner cylinder holds the photosynthetic-parenchyma cells.
These cells are responsible for starting the growth of leaves, which grow along the sides of the stem in transverse lines – though this can only be seen under a microscope.
The stem is anchored to substrates through rhizoids, which are hardy structures that are responsible for absorbing nutrients from the substrates.
This is why moss is typically hard to pull away from the surface.
Rhizoids can be either smooth or rough depending on the species, and the location also varies, too.
For example, acrocarps feature a rhizoid located attaching the base of the stem to the substrate. Some species have a rhizoid found along the stem region.
Bryophyta species also lack true vascular tissue, meaning the water and nutrients transportation is achieved through cell-to-cell transport.
This isn’t an effective method of transportation, which is why moss grows in moist habitats so they have easy access to water.
It also helps that mosses are so small (around 2-4 inches in height), so there is no need for large vascular tissue.
Chloroplasts are also abundant in the leaves, which is why moss is permanently green as a result of photosynthesis.
Bryphotes reproduce either sexually or asexually, but they don’t produce flowers or seeds to reproduce.
For asexual reproduction, most bryophytes are hermaphrodites, exhibiting both male sex organs (antheridia) and female sex organs (archegonia).
However, some species don’t feature both sets of sex organs, which is when plants reproduce sexually.
The gametes, or the male sex organs, are produced on the gametophyte, which is made up of the stems and leaves of mosses. Female mosses feature spore capsules that develop from a fertilized egg.
During sexual reproduction, the spores from the gametes are moved to the spore capsules to germinate, which is usually achieved through the movement of water and wind.
For mosses that feature both male and female sex organs, this is called asexual reproduction. The sporophyte (which is home to the spore capsule) is attached to the gametophyte, where it draws the nutrients from.
Water is the key for asexual reproduction, as the antheridia’s gametes seek out the archegonia’s eggs when it rains. The gametes rely on the water for movement.
Asexual reproduction occurs when the gamates from the gametophyte fall to the ground, which then leads to germination as new plants begin to grow on the floor.
To put it simply – sexual reproduction occurs when gametes fuse to form a zygote, and asexual reproduction occurs when sporophytes release spores.
Members of Phylum Marchantiophyta are often classified in the Bryophyta Phylum, and this is because Marchantiophyta species are commonly known as liverworts, which were initially classified alongside mosses.
The reason for this is that liverworts use the same process as mosses to transport nutrients and water through a process called diffusion.
This is also why liverworts are commonly found in moist areas with constant access to water.
There are roughly over 10,000 liverwort species that make up the Marchantiophyta Phylum, including:
- Common liverwort
- Complex thalloids
Liverworts, like mosses, are typically small plants that range in width from 2 mm to 22 mm.
This is down to the process of diffusion to garner nutrients and water, as the smaller the plant, the easier it is to hydrate and survive.
Liverworts look rather leafy, but interestingly, most liverwort species don’t actually exhibit true leaves or stems. Instead, the “leaves” are thalloid (lacking stems, leaves, and roots) and feature a thallus, which is a vegetative tissue that resembles leaves.
While there aren’t roots, liverworts possess rhizoids, which are responsible for garnering nutrients from the substrate.
The reason liverworts manage to stay so green throughout the year is because the thallus contains chlorophyll pigments in photosynthetic tissue, allowing the plant to photosynthesize.
The similarities between liverworts and mosses doesn’t stop at the process of diffusion – both plants can also reproduce sexually and asexually.
Asexual reproduction in liverworts occurs when the modified bud of tissue known as gemmae falls to the ground. When it finds a place on the ground, it germinates and rises as a new individual.
Gemmae are found in goblet-like structures located on the thallus, which are the “leaves” of the liverwort.
This is most commonly found on thallose liverworts. When wind or rain moves the liverwort, the bud tissue is knocked to push out the gemmae.
This is another reason why liverwort grows in favorable moist conditions, because the amount of rain allows for lots of germination.
As for sexual reproduction, the gametes of liverwort and produced in structures that resemble umbrellas grown from the thallus.
The male gametes are released from the umbrella structures and swim along the surface of the thallus to the female sex organs, wherein they fertilize the eggs.
During the fertilization process, the embryo becomes a capsule with the spores, which then develop into new individuals.
The individuals fall onto a suitable surface when dispersed, which is fairly similar to the asexual reproduction.
The key to liverwort reproduction is accessibility to water. Without water on the thallus, the gametes cannot travel to the eggs. This is also why liverworts thrive in moist conditions, and why new plants grow so frequently.
As with the Marchantiophyta Phylum, the Anthocerotophyta Phylum – also known as hornworts – was once initially classified in the Phylum Bryophyta.
Based on new genetic evidence, however, hornworts have been classified in their own Phylum.
One of the several similarities between hornworts, liverworts, and mosses is that they are all simple plants that live in favorable conditions around the world, specifically moist soil and shaded areas.
Some species of hornworts include:
- Anthoceros angustus
- Anthoceros agrestis
- Phaeoceros laevis
- Megaceros flagellaris
- Phaeoceros carolinianus
Like mosses and liverworts, hornworts are generally very small plants that grow in clusters, only typically ranging in size from 5-10 cm in length.
These simple plants don’t possess stems, leaves, or roots (making hornworts thalloids), but instead have irregularly shaped thallus for “leaves” and rhizoids for “stems”, which attach the plant to the substrate.
However, unlike liverworts, hornworts lack pores, and some species even have stomata – which is an apomorphy of all land plants apart from liverworts.
While both hornworts and liverworts have symbiotic relationships with blue-greens (cyanobacteria) that live inside the thallus cavities, this isn’t a relationship present in mosses.
Just as with mosses and liverworts, hornworts are known to reproduce both sexually and asexually.
For sexual reproduction, the male gametes are dispersed from the antheridium and travel to the female sex organ (archegonium) to fertilize the egg.
This can only be achieved in moist conditions, hence their preferred habitat, as the gametes can only travel through droplets of water or wind.
Once fertilized, the archegonium produces a sporangium that separates to disperse spores. These spores are then released into the air before falling to the ground to create a new individual if successful.
Asexual reproduction occurs through a process called fragmentation, which is when a rooted shoot becomes detached from the main group, usually in dry conditions.
This leaf (or in this case, thallus) releases gemmae, which then create new individuals in the right conditions. However, as hornworts reside in moist conditions, asexual reproduction is less favorable than sexual reproduction.
Phylum Pteridophyta consists of roughly 12,000 species of ferns.
These species are simple plants in comparison to trees and taller organisms, but are far more complex than true simple plants like moss, liverwort, and hornwort.
The species in this Phylum are found in temperate forests and moist tropical environments, but some species can be found in the Antarctic and Arctic regions.
Here are some examples of Pteridophyta species:
- Marsilea crenata
- Whisk fern
- Dicksonia sellowiana
- Cyathea spinulosa
- Salvinia natans
Pteridophytes are classified as sporophytes, meaning they have a body consisting of leaves, roots, and a stem – which is also known as a rhizome.
These rhizomes vary in size and thickness depending on the species, with some growing to heights of 20 meters.
Rhizomes are anchored and attached to the soil thanks to adventitious roots. These roots are covered in dense structures that resemble hairs for extra grip.
The stems can range in shape depending on the species – for example, Horsetails have ridged stems, while Grape ferns have tuberous stems.
In most species in the Phylum, the vascular system runs along the length of the rhizome and is a hollow cylindrical shape.
This vascular system is responsible for transporting water and nutrients, as it holds the xylem and phloem, to the stem and leaves.
This is why Pteridophyta species prefer to grow in moist tropical climates, so they have constant access to water and nutrients.
The leaves in true ferns are vital organs in this Phylum. Each species features their own leaf size and shape, therefore varying in complexity.
For example, primitive fern species feature small, needle-like leaves, while other species like Gleicheniaceae possess leaves over 1 meter long.
Other characteristics in fern leaves include a layer of hair or a smooth coating, complex venation, unique patterns, and varying degrees of thickness according to its habitat.
As with most Kingdom Plantae Phylum, Pteridophytes can reproduce both asexually and sexually.
There are three types of asexual reproduction, including reproduction from rhizomes, apogamy, and reproduction from the frond tips.
When reproducing from rhizomes, the species will simply rely on the rhizome to spread through the soil to create new individuals.
This is achieved through modified stems that shoot upwards, which is why most ferns are clumped together.
Apogamy refers to cell divisions in the sporangia, which leads to the production of spores that have the same genetic composition as the sporophyte.
The spores can produce new sporophytes with the gametophyte when in the right, dry conditions.
Similar to fragmentation, the final form of asexual reproduction is when the fronds bend to the floor as the plant grows and gets heavier.
The fronds then become rooted to the ground, and if the conditions are right, it will naturally start developing a new individual that will separate from the original plant.
As for sexual reproduction, ferns will reproduce from the fusion of female and male gametes.
This process follows the sexual reproduction process of most Phylum in the plant kingdom, wherein the male gametes in the antheridia fuse together with the female gametes in the archegonia.
This results in the development of zygotes, which then form into sporophytes.
Interestingly, members of the Phylum Chlorophyta (otherwise known as green algae) aren’t actually true plants.
However, green algae are organisms formed from plants, which is why they are brought into the same conversation as plants.
This Phylum isn’t, therefore, technically part of the plant kingdom, but it once was.
Members of this group include multicellular algae, macroscopic seaweeds, and single-celled flagellates.
The species are known to form symbiotic relationships with fungi and even other animals. They are found in a range of habitats, including rocks, trees, soil, freshwater, and marine environments.
Here are some species of the Phylum Chlorophyta:
- Fucus species
- Chlamydomonas species
- Volvox species
- Ulothrix species
One reason why Chlorophyta was once considered part of the Kingdom Plantae is because the members can reproduce both sexually and asexually.
As for sexual reproduction, green algae fertilizes its female eggs through the process of fusion.
This is when the male and female gametes are fused together by the means of a flagellum, which enables movement.
Green algae species can asexually reproduce in two ways.
One of these ways is through the germination of spores, wherein spores are distributed by the flagellum to the ground, which gives rise to new individuals.
The second way is through fragmentation, when parts of the parent plant grow into the surrounding environment to produce new individuals, which eventually separate themselves from the parent plant.
So, there you have it! As Kingdom Plantae is such a large Kingdom, it makes sense why it consists of multiple Phylum.
Here’s a basic summary of each Phylum in Kingdom Plantae and what they consist of:
- Angiosperms are the largest Phylum in the Kingdom, consisting solely of flowering plants. The species are divided into three categories – Monocots, Dicots, and Basal Angiosperms according to the number of embryonic leaves.
- Gymnosperm is a Phylum consisting of conifers, known for producing naked seeds such as pine cones. The species in this Phylum grow in woody areas and are the tallest of all plant species.
- Bryophyta is a Phylum consisting of mosses that don’t possess leaves, stems, roots, or vascular tissues. Instead, they obtain water and nutrients through a rhizome structure, and equally rely on water for sexual reproduction.
- Marchantiophyta is a Phylum of liverwort plants that, like mosses, rely on their rhizome structures for water and nutrients.
- Anthocerotyphyta is a Phylum of hornworts that are similar to liverworts and mosses, but with their own characteristics.
- Pteridophyta is another large Phylum in the Kingdom consisting of fern species, all of which vary greatly in shape, size, and structure.
- Chlorophyta, or green algae, was once considered a Phylum in the Kingdom Plantae. As green algae still share similarities with true plants, the Phylum is still often referred to in the plant kingdom.
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