The land plants or embriofitas make up the group most diverse and abundant plants on earth which include, among others, all flowering plants, all the trees, ferns and mosses. With the exception of some terrestrial algae, virtually all plants on earth belong to the group Embryophyta (embryophyta).
This group, currently represented by more than 300 thousand living species, contains organisms with a great diversity of shapes and sizes, since it includes both sequoias (the tallest trees in the world) and tiny plants belonging to the genus Wolfia ( less than 1 mm3 in volume).
Fossil records show that the first embryophytes to live on earth did so roughly 460 million years ago and that their early evolution had important consequences for many aspects of the environment.
Among them the development of soils, the evolution of the atmosphere (due to the production of oxygen through photosynthesis), the emergence and radiation of the first terrestrial animals (with mainly herbivorous diets), and radical changes in the short and long-term in carbon cycling.
Characteristics of land plants
Embryophytes are photoautotrophic multicellular organisms (capable of producing their own “food”) with cells protected by a cellulose cell wall.
All terrestrial plants are characterized by the production of multicellular embryos, which are retained for variable times in a specialized tissue known as the female gametophyte (the haploid stage of a plant), which is why they are known as embryophytes.
Not only vascular plants or tracheophytes belong to this group, but also mosses or bryophytes, which is why it is characterized by its great diversity of shapes, sizes and life habits.
They inhabit the earth
Terrestrial plants, as their name indicates, inhabit the earth, attaching themselves to it and obtaining water and mineral nutrients from it through the organs we know as roots.
A large amount of structural, biochemical and molecular evidence supports the hypothesis that all terrestrial plants descend from a common ancestor very similar to chlorophyte green algae, among which are unicellular and filamentous organisms and others with more complex structures.
In addition, among other of its characteristics are:
– Alternation of generations in their life cycle
– Apical cell growth
– Presence of antheridia (organs of the male gametophyte)
– Presence of archegonia (organs of the female gametophyte)
Embryophytes are an extremely large and diverse group of plants, with a great variety of sizes, shapes, habits, reproduction mechanisms, nutritional characteristics, and different adaptations.
However, and despite these differences, important molecular, biochemical and morphological evidences suggest that it is a monophyletic group, that is, that all its members descend from the same common ancestor.
At present it is estimated that this group is composed of more than 300,000 living species, which can be considered “separate” or “divided” into two main groups, which can be distinguished with respect to the nature of their life cycle:
– bryophytes or mosses (Bryophyta)
– tracheophytes or vascular plants (Tracheophyta)
– Bryophyta: mosses, liverworts and hornworts
The bryophytes group includes three subgroups of non-vascular terrestrial plants: the mosses, the liverworts and the hornworts. There are about 10,000 species of mosses, about 8,000 species of liverworts and between 300 and 400 species of hornwort.
Mosses are relatively small non-vascular plants (up to 60 cm high) and moderately leafy, whose distinctive feature is the mechanism they use for the release of spores, which is one of the most elaborate within the bryophyte group.
This mechanism consists, in a large number of species, in a capsule that contains the spores and that has an apical “gate” called an operculum.
Liverworts can be of two types of body architecture: talose and foliose. The former have a lobed and flattened shape, while the latter have two stems containing two or three rows of non-innervated leaves.
In liverworts, the spore-bearing phase is extremely ephemeral and consists of a spherical or ellipsoid capsule containing microscopic spores, which emerges from a portion of the tissue before the release of the spores.
The anthoceras form a small group of non-vascular plants, with species of architecture very similar to that of the talose liverworts, although with a much more elaborate capsule for the spores.
This group is comprised of all terrestrial vascular plants, classified into three large subgroups:
– Pteridophytes (Pteridophyta): club mosses, horsetails and ferns.
– Spermatophyta: gymnosperms (conifers and others) and angiosperms (flowering plants)
In pteridophytes, the phase of the life cycle that supports the gametes and that that supports the spores occur in separate plants, contrary to gymnosperms and angiosperms, where both are fused in the same individual.
Thanks to the similarities regarding their life cycle, club mosses, horsetails and ferns are grouped together in the group of pteridophytes. About 1,500 species of club mosses, 15 species of horsetails and more or less 15,000 species of ferns have been described.
Club mosses are plants very similar to mosses, so they can be described as small herbaceous plants (no more than 1 meter high), characterized by simple leaves, similar to thorns or scales.
Sporophytes form at the base of specialized leaves, which are often grouped into a cone.
The horsetails, also called “horsetail” are an extremely small group of small herbaceous plants that have branches arranged in a spiral arrangement and are characterized by having leaves similar to a tiny scale.
Sporophytes in horsetails, as well as club mosses, form in cone-like structures.
Ferns comprise a very heterogeneous group of plants that are characterized by the presence of highly branched leaves. In these organisms, sporophytes grow on leaves, not cones (as in club mosses and horsetails).
Spermatophyta: gymnosperms and angiosperms
Spermatophytes are the plants that produce seeds. In these, the gametophyte phase (the one that contains the gametes for sexual reproduction) is born in a special structure that we call “seed”. There are almost 800 living species of gymnosperms and more than 250,000 species of angiosperms.
The group of gymnosperms includes conifers, cycads, gnetals and ginkgos ( Ginkgo biloba the only species). They are, for the most part, trees or shrubs that reproduce by seeds and whose pollen-forming structures are inside a cone.
To this group belong, for example, the largest arboreal specimens in the world: the sequoias, as well as many conifers that are familiar to us when we think of a temperate forest in North America.
Angiosperms, also known as flowering plants, are classified as the largest group of land plants in existence. These produce flowers, from which fruits and seeds (which are covered by specialized structures) are formed.
Life cycle of land plants
All bryophyte species have a life cycle that alternates between two phases, one sexual and one asexual.
The sexual phase implies a specialized structure in the “support” of the gametes (the gametophyte), meanwhile the asexual phase implies a specialized structure in the “support” of the spores (the sporophyte).
In bryophytes, the largest and / or most visible “phase” of the life cycle is the gametophyte, contrary to what happens with tracheophytes, where the sporophyte phase is the one that characterizes the free-living plant structure and large size (compared to the gametophyte phase).
Embryophytes or terrestrial plants depend, essentially, on their photosynthetic capacity to survive, that is, on their ability (through photosynthesis) to convert the light energy contained in the sun’s rays into chemical energy in the form of ATP.
During this process, in addition, they carry out the synthesis or fixation of carbon dioxide (CO2) in large energetic molecules that function as a reserve and of which man and other herbivorous and / or omnivorous animals use to live.
However, to be able to photosynthesize, terrestrial plants need water and to be able to synthesize the structures that characterize them, they also need minerals, which they obtain from the soils or substrates where they live through their roots.
Among the main minerals that a terrestrial plant needs to survive we can mention:
Terrestrial plants share many distinctive adaptive characteristics that allow them to live in the environment where they live, that is, in permanent contact with the atmosphere and with the soil where they have “put down their roots.” Here is a short list of some of them:
– All have a waxy cuticle that prevents the loss of water by evaporation from the surface of their tissues.
– The relationship between surface area and volume is lower than that of many algae, which allows the development of multicellular bodies with a parenchyma .
– Most land plants exchange gases with the atmosphere through “pores” or openings in the leaves known as stomata .
– They have an internal vascular system for the transport of water and processed matter that, in most plants, consists of an interconnected system of elongated cells (those of the xylem and those of the phloem).
– Many terrestrial plants have structures specialized in the protection of gametes , that is, of the ovules and sperm cells that function in sexual reproduction.
– These plants have a much more developed body structure than aquatic plants, which implies a greater development of structurally resistant tissues , mainly due to the thickening of the cellulose walls and the deposition of other biopolymers such as lignin, which are much more resistant .
– For the formation of larger plants, necessarily better and more extensive and complex radical systems were developed , since these not only function in the anchoring of the plants to the substrate, but also in the absorption and initial conduction of water and mineral nutrients.
– Virtually all terrestrial plants have leaves , whose development meant a great innovation for life on earth.
– Gymnosperms and angiosperms reproduce through a special structure called the seed which, before fertilization, corresponds to the ovule (female gametophyte) wrapped in layers of tissue derived from the sporophyte.
Examples of land plant species
Since land plants represent the largest group of plants in the biosphere, there are countless species that we can cite as examples of this group.
Mosses belonging to the genus Sphagnum , also called “peat mosses” are known for their great water retention capacity, which is exploited in the floristics and horticulture industry for the “formulation” of light substrates to propagate other plants.
Nephrolepis cordifolia , commonly known as “serrucho fern” is a very common pteridophyte species found mainly in Central and South America, in different types of terrestrial environments, especially forests.
The avocado, curo or avocado is a terrestrial plant of the group of angiosperms belonging to the Persea americana species . This plant, of great economic interest around the world, produces highly coveted fruits not only for its flavor, but also for its nutritional properties.
Araucaria araucana , a gymnosperm also known as araucaria pine, araucano pine or pehuén, is a tree considered “ancient” in Patagonia Argentina that produces edible seeds (pine nuts), which have a high nutritional value.
- Becker, B., & Marin, B. (2009). Streptophyte algae and the origin of embryophytes. Annals of botany, 103 (7), 999-1004.
- Gensel, PG (2008). The earliest land plants. Annual Review of Ecology, Evolution, and Systematics, 39, 459-477.
- Graham, LE, Kaneko, Y., & Renzaglia, K. (1991). Subcellular structures of relevance to the origin of land plants (embryophytes) from green algae. Critical Reviews in Plant Sciences, 10 (4), 323-342.
- Kenrick, P. (2001). Embryophyta (Land Plants). e LS.
- Nabors, MW (2004). Introduction to botany (No. 580 N117i). Pearson.
- Raven, PH, Evert, RF, & Eichhorn, SE (2005). Biology of plants. Macmillan.