Evolutionary Tree of Plants

1.1. The Position of Plants in the System of Living Nature

Before discussing the transition to land, it is necessary to define clearly which organisms are meant. Modern biology recognizes several kingdoms of living nature. According to current views, plants are a separate kingdom (Plantae), characterized by autotrophic nutrition based on oxygenic photosynthesis, a rigid cell wall, and an attached mode of life (Serebryakova et al., 2006; Yakovlev et al., 2006).

It is important to understand that historically botanists studied not only plants in the narrow sense but also fungi and bacteria. However, modern systematics clearly distinguishes these groups. Fungi are heterotrophic organisms that store glycogen rather than starch and have chitin in the cell wall (Yakovlev et al., 2006). Bacteria are prokaryotes without a true nucleus. Plants, in contrast, are eukaryotes that carry out oxygenic photosynthesis with the release of oxygen (Serebryakova et al., 2006).

For our purposes, it is important to emphasize that plants are a monophyletic group, that is, they descend from a single common ancestor. This ancestor was an aquatic organism, and it was from the aquatic environment that plants began their path onto land.

1.2. Problems of the Terrestrial Environment

The transition to land is not merely a change of scenery. The terrestrial environment differs radically from the aquatic one in a number of parameters, and each of them poses a serious challenge to an organism (Yakovlev et al., 2006; Raven et al., 2007).

Desiccation. In water, an organism is surrounded by liquid that is constantly available. On land, water may be available only periodically or may be present in the soil, but not around the entire body. Evaporation from the body surface becomes a serious problem. As a consequence, protective coverings are needed—a cuticle that limits water loss (Raven et al., 2007).

Gravity. In water, gravity is largely compensated by buoyancy. On land, an organism needs mechanical support to resist gravity. This leads to the need for supporting tissues and, ultimately, to the appearance of a vascular system (Serebryakova et al., 2006).

Ultraviolet radiation. In water, UV radiation is partially absorbed. On land, an organism is exposed to direct UV rays, which damage DNA and proteins. This requires the development of protective pigments and, possibly, the ability to repair damage (Raven et al., 2007).

Gas exchange. In water, CO₂ and O₂ are dissolved and available through the body surface. On land, gas exchange is more difficult because CO₂ is present in the atmosphere at a low concentration, and water vapor is lost during gas exchange. This creates a dilemma: how to obtain enough CO₂ without losing too much water? The solution is stomata, regulated pores (Raven et al., 2007).

Reproduction. In water, sperm can swim to the egg. On land, this requires water, or new ways of delivering gametes must be invented. This is one of the key problems that will be solved throughout plant evolution (Yakovlev et al., 2006).

1.3. Preadaptations in Green Algae

The key question is: from whom did land plants descend? Modern molecular phylogeny gives an unambiguous answer: the closest relatives of land plants are a group of green algae known as streptophytes (Streptophyta), and especially charophytes (Charophyceae) (Judd et al., 2018; Becker et al., 2025).

Streptophytes are a clade that includes both aquatic forms and land plants. Within streptophytes, several groups are distinguished: Mesostigma, Chlorokybus, Klebsormidiales, Charales, Coleochaetales, and Zygnematales. According to current data, the closest relatives of land plants are Charales and Coleochaetales, or Zygnematales (Judd et al., 2018; Becker et al., 2025).

Why was it these algae that could give rise to land plants? The reason is that they already possessed preadaptations—traits that performed one function in the aquatic environment but proved useful for completely different tasks on land (Raven et al., 2007; Ligrone et al., 2012).

Cell division with a phragmoplast. In charophytes, unlike most other green algae, cell division occurs with the formation of a phragmoplast—a structure that guides the formation of the cell plate between daughter cells. This leads to the formation of plasmodesmata—cytoplasmic bridges between cells. Plasmodesmata provide intercellular transport and communication, which is critically important for multicellular organisms (Ligrone et al., 2012).

Apical growth. In Charales and Coleochaetales, growth occurs through division of the apical cell. This creates the basis for forming a complex body with differentiated tissues (Judd et al., 2018).

Retention of the zygote on the maternal organism. In Charales and Coleochaetales, the zygote does not immediately leave the maternal organism but remains on it for some time, receiving nutrients. This is the rudiment of embryonic development, which is characteristic of all land plants (Renzaglia et al., 2000).

Presence of cutin and phenolic compounds. Some charophytes are capable of synthesizing substances related to cutin—a component of the cuticle. This may be a preadaptation for protection against desiccation (Ligrone et al., 2012).

UV resistance. Charophytes have mechanisms of protection against UV radiation, including the synthesis of phenolic compounds (Raven et al., 2007).

1.4. Direction of Evolution: From Haploid to Diploid Dominance

One of the key events during the transition to land was a change in the life cycle. All modern land plants exhibit alternation of generations: a haploid gametophyte and a diploid sporophyte. However, the ratio of these generations differs radically among different groups.

In charophytes (and most algae), the life cycle is haploid: the only diploid cell is the zygote, which immediately undergoes meiosis. In land plants, a multicellular diploid sporophyte appears. This became possible due to a delay in meiosis and the insertion of mitotic divisions after zygote formation (Bennici, 2008; Ligrone et al., 2012).

There are two main theories of the origin of alternation of generations:

1. Antithetic (interpolation) theory—the sporophyte arose as a new stage inserted into the haploid life cycle through a delay in meiosis (Bower, 1890, cited in Bennici, 2008).

2. Homologous (transformation) theory—alternation of generations already existed in ancestors, but both generations were isomorphic (Bennici, 2008).

Modern data, including paleobotanical finds, support the antithetic theory: in early land plants (for example, rhyniophytes), the gametophyte and sporophyte were relatively similar in size, but later evolution proceeded toward enlargement of the sporophyte and reduction of the gametophyte (Bennici, 2008; Ligrone et al., 2012).

1.5. Significance of the Transition to Land for Evolution and Agriculture

The emergence of plants onto land had enormous consequences. First, it led to the formation of terrestrial ecosystems, which became the basis of the entire modern biosphere. Second, it created the prerequisites for the appearance of the entire diversity of land plants—from mosses to angiosperms (Judd et al., 2018).

But what does this have to do with agriculture? The most direct relation. All cultivated plants are land plants. Their evolutionary history is the history of adaptations to the terrestrial environment. Understanding these adaptations allows us to:

• Understand why plants need certain conditions (water, mineral nutrition, gas exchange).
• Identify traits that were selected by humans during domestication (for example, large seeds, non-dehiscing fruits).
• Use evolutionary principles for breeding (hybridization, polyploidy, selection).

Thus, the transition to land is not merely an abstract event of antiquity. It is the foundation on which all modern crop production stands. And understanding this foundation is necessary for a systematist and a specialist in the agrosphere.

Conclusion

So, we have examined the first and most important stage of plant evolution—the transition from water to land. We saw that this transition became possible thanks to preadaptations that formed in charophyte algae: the phragmoplast and plasmodesmata, apical growth, retention of the zygote, protective coverings. We also discussed the key problems of the terrestrial environment—desiccation, gravity, UV, gas exchange, and reproduction—and how these problems were solved during evolution.

2.1. Bryophytes as a Paraphyletic Group

First of all, an important clarification is necessary. Traditionally, bryophytes were considered a single group—division Bryophyta. However, modern molecular phylogenetic studies have shown that bryophytes are a paraphyletic group, that is, a grade of successive branchings, not a clade (Judd et al., 2018; Shaw et al., 2011; Renzaglia et al., 2000).

This means that the three groups of bryophytes—liverworts (Marchantiophyta), mosses (Bryophyta), and hornworts (Anthocerotophyta)—diverged from a common ancestor sequentially, and some of them are closer to vascular plants than to each other. According to current data, liverworts are the earliest diverging group, then mosses, and hornworts are the sister group to vascular plants (Renzaglia et al., 2000; Shaw et al., 2011; Ligrone et al., 2012).

This is important to understand for systematics: when we speak of “mosses” in the broad sense, we mean a grade of evolutionary development, not a natural group. At the same time, each of the three groups—liverworts, mosses, and hornworts—is monophyletic, that is, descends from a common ancestor and includes all its descendants (Judd et al., 2018).

Nevertheless, all three groups possess a number of common features that distinguish them from vascular plants. These features reflect their position at the early stages of land flora evolution and their ecological strategy.

2.2. Key Characteristics of Bryophytes

Bryophytes retain a number of features that were characteristic of the first land plants. Let us consider them in more detail.

2.3. Three Groups of Bryophytes

Let us now consider each of the three groups of bryophytes in more detail.

2.4. Modern Significance of Bryophytes

Although bryophytes did not become the basis of agriculture, they play an important role in modern ecosystems and have practical significance.

Environmental indicators. Bryophytes are very sensitive to air pollution and changes in humidity. Their species composition can be used to assess the state of the environment. For example, the disappearance of certain moss species may indicate air pollution with sulfur dioxide (Yakovlev et al., 2006).

Peat. Sphagnum mosses form peat bogs, which are important ecosystems. Peat is used as fuel, fertilizer, and raw material for the chemical industry. In addition, peat bogs play an important role in the global carbon cycle, accumulating carbon (Mauseth, 2016; Yakovlev et al., 2006).

Ornamental plants. Some mosses and liverworts are used in ornamental gardening, especially in landscape design and in creating “mossy” gardens. They are also used in aquarium keeping (Yakovlev et al., 2006).

Medicinal plants. Some bryophytes are used in folk medicine. For example, Marchantia polymorpha is used as a medicinal plant, and Sphagnum as an antiseptic (Yakovlev et al., 2006).

Scientific significance. Bryophytes are an important object for studying the evolution of land plants. They retain many archaic features and allow us to understand how the transition from aquatic ancestors to land plants occurred (Renzaglia et al., 2000; Ligrone et al., 2012).

2.5. Why Mosses Did Not Become the Basis of Agriculture

Now let us answer an important question: why did bryophytes, being the first land plants, not become the basis of agriculture?

There are several reasons. First, the absence of a true vascular system limits the size of bryophytes. They cannot reach large sizes like vascular plants and, consequently, cannot produce large amounts of biomass suitable for human nutrition (Mauseth, 2016).

Second, dependence on water for reproduction makes bryophytes vulnerable to changes in humidity. Agricultural plants must be independent of water for reproduction so that they can be grown under controlled conditions (Yakovlev et al., 2006).

Third, the absence of true roots limits the ability of bryophytes to extract water and minerals from the soil. This makes them less productive than vascular plants (Mauseth, 2016).

Fourth, dominance of the gametophyte means that bryophytes cannot effectively use the diploid generation for biomass accumulation. In vascular plants, it is the sporophyte that is the dominant generation, and it produces the main part of the biomass (Ligrone et al., 2012).

Finally, the absence of seeds means that bryophytes cannot form storage organs that can be stored and transported. Seeds are a key invention that made agriculture possible (Yakovlev et al., 2006).

Thus, bryophytes are an important stage in the evolution of land plants, but their evolutionary limitations did not allow them to become the basis of agriculture. That role fell to vascular plants, which we will examine in the next lecture.

3.1. What are vascular plants?

Vascular plants (Tracheophyta) are a clade that includes all modern land plants except the bryophytes. They include lycophytes, horsetails, ferns, gymnosperms, and angiosperms (Judd et al., 2018; Raven et al., 2007).

The name “vascular” reflects the key innovation of this group — the presence of a vascular system consisting of xylem and phloem. It is this system that ensures the transport of water, mineral substances, and products of photosynthesis throughout the plant body (Mauseth, 2016; Raven et al., 2007).

Vascular plants are characterized by a number of common features that distinguish them from bryophytes:

1. Dominance of the sporophyte in the life cycle.

2. Presence of true vessels — xylem and phloem.

3. Presence of true roots, stems, and leaves (in most groups).

4. Lignified cell walls — lignin gives strength and rigidity to conducting and mechanical tissues.

5. Branched sporophyte, producing numerous sporangia (Judd et al., 2018; Mauseth, 2016; Ligrone et al., 2012).

These features formed gradually during evolution, and their appearance can be traced through fossil remains. Let us examine each of them in more detail.

3.2. Xylem and phloem: the conductivity revolution

The key event in the evolution of vascular plants was the appearance of the conducting system, consisting of two types of tissues: xylem and phloem (Raven et al., 2007; Mauseth, 2016).

3.3. The appearance of roots, stems, and leaves

The appearance of the vascular system is also connected with the appearance of true vegetative organs — roots, stems, and leaves. In bryophytes these organs are absent or represented by rhizoids and phylloids, which are not homologues of true roots and leaves (Raven et al., 2007; Judd et al., 2018).

3.4. Dominance of the sporophyte in the life cycle

One of the key differences between vascular plants and bryophytes is the dominance of the sporophyte in the life cycle. In vascular plants, it is the sporophyte (diploid generation) that is the large, long-lived, and photosynthetic organism. The gametophyte (haploid generation) is reduced and often incapable of independent existence (Judd et al., 2018; Ligrone et al., 2012).

This change occurred during evolution and has important consequences. The sporophyte, being diploid, possesses genetic buffering: harmful mutations can be compensated for by normal alleles. This gives the sporophyte an evolutionary advantage (Ligrone et al., 2012).

In addition, the sporophyte of vascular plants is capable of indeterminate growth thanks to apical meristems. This allows it to reach large sizes and produce a large number of spores (Judd et al., 2018).

In the most ancient vascular plants — the rhyniophytes — the sporophyte and gametophyte were relatively similar in size. However, subsequently evolution followed the path of increasing the sporophyte and reducing the gametophyte. In modern vascular plants, the gametophyte is often represented by only a few cells (Ligrone et al., 2012; Bennici, 2008).

3.5. The first vascular plants: rhyniophytes

The most ancient vascular plants known from fossil remains belong to the group rhyniophytes (Rhyniophyta). They appeared in the Late Silurian — about 425–420 million years ago — and became extinct in the Middle Devonian — about 380 million years ago (Kenrick & Crane, 1997; Raven et al., 2007).

Rhyniophytes were small plants, usually no more than 20–50 cm tall. They had dichotomously branching stems without leaves and roots. Sporangia were located at the ends of the branches. The conducting system was represented by a protostele — a solid cylinder of xylem consisting of tracheids with annular or spiral thickenings (Kenrick & Crane, 1997; Raven et al., 2007).

The most well-known genera of rhyniophytes are Cooksonia, Rhynia, Aglaophyton (formerly Rhynia major), and Horneophyton. Cooksonia is considered the most ancient known vascular plant: its remains have been found in Late Silurian deposits (Raven et al., 2007).

It is important to note that in some rhyniophytes, for example in Aglaophyton, the conducting cells did not have lignified secondary walls and were similar to the hydroids of mosses. This indicates that the appearance of a true vascular system was a gradual process (Kenrick & Crane, 1991; Edwards, 1986).

Rhyniophytes probably grew near water — along the shores of water bodies, on moist soils. They could not live in arid habitats because of the absence of true roots and dependence on water for reproduction (Raven et al., 2007).

3.6. Lycophytes: the first true leaves and roots

Lycophytes (Lycopodiophyta) are an ancient group of vascular plants that appeared in the Devonian and reached their peak in the Carboniferous. Modern lycophytes are represented by several genera: Lycopodium (clubmoss), Selaginella (spikemoss), Isoetes (quillwort), and others (Judd et al., 2018; Raven et al., 2007).

Lycophytes are characterized by the presence of microphylls — small leaves with one vein. They also have true roots with an apical meristem and lateral sporangia, which are located in the axils of leaves or on their upper surface (Judd et al., 2018; Kenrick & Crane, 1997).

In the Carboniferous, lycophytes were represented by arborescent forms, such as Lepidodendron and Sigillaria. These trees reached 30–40 meters in height and formed extensive forests. Their remains became the basis for the formation of coal (Raven et al., 2007; Mauseth, 2016).

Arborescent lycophytes had secondary growth — the ability to increase the thickness of the stem through the activity of the cambium. However, their cambium was unifacial: it produced only secondary xylem, but not secondary phloem. This limited their growth and probably became one of the reasons for their extinction (Raven et al., 2007; Mauseth, 2016).

3.7. Horsetails: jointed stems

Horsetails (Equisetophyta) are a group of vascular plants that appeared in the Devonian and reached their peak in the Carboniferous. Modern horsetails are represented by a single genus Equisetum (horsetail), numbering about 15 species (Judd et al., 2018; Raven et al., 2007).

Horsetails are characterized by jointed stems with whorled leaves. The stems have a ribbed surface and contain silica, which gives them rigidity. Sporangia are located on sporangiophores gathered into strobili at the top of the stems (Judd et al., 2018; Mauseth, 2016).

In the Carboniferous, horsetails were represented by arborescent forms, such as Calamites. These trees reached 20 meters in height and had secondary growth with a bifacial cambium, which produced both secondary xylem and secondary phloem (Raven et al., 2007; Mauseth, 2016).

Modern horsetails are small herbaceous plants that grow in moist habitats. They have rhizomes with tubers, which store starch. Some species of horsetails are used in medicine as a diuretic (Yakovlev et al., 2006).

3.8. Ferns: large leaves and diversity

Ferns (Polypodiophyta) are the most diverse group of spore-bearing vascular plants. They appeared in the Devonian and reached their peak in the Carboniferous. Modern ferns number more than 12,000 species and are distributed throughout the world (Judd et al., 2018; Testo & Sundue, 2016).

Ferns are characterized by megaphylls — large leaves with a branched system of veins. The leaves of ferns are called fronds. They are usually pinnate or multiply pinnate. Young fern leaves are circinately coiled — this phenomenon is called circinate vernation (Judd et al., 2018; Mauseth, 2016).

The sporangia of ferns are usually gathered into sori on the lower side of the leaves. In some ferns, the sporangia are located on specialized leaves — sporophylls. Ferns can be homosporous (producing one type of spore) and heterosporous (producing microspores and megaspores) (Judd et al., 2018; Testo & Sundue, 2016).

In the Carboniferous, ferns were represented by arborescent forms, such as Psaronius. These trees reached 8 meters in height and had complex steles with leaf gaps. Their remains also became the basis for the formation of coal (Raven et al., 2007; Mauseth, 2016).

Modern ferns are predominantly herbaceous plants, although among them there are also arborescent forms (for example, Cyathea). They grow in moist tropical forests, where they reach their greatest diversity (Testo & Sundue, 2016).

3.9. The Carboniferous period: forests and the formation of coal

The Carboniferous period (about 360–290 million years ago) was the time when vascular plants reached their greatest prosperity. During this period, extensive forests formed, consisting of arborescent lycophytes, horsetails, and ferns (Raven et al., 2007; Mauseth, 2016).

These forests grew in waterlogged habitats — on lowlands covered by shallow seas or swamps. The climate was warm and humid, which favored plant growth. In these forests there were no flowering plants — they appeared later (Raven et al., 2007; Yakovlev et al., 2006).

The remains of these forests, accumulating under conditions of oxygen deficiency (in swamps), did not decompose completely. Over time they were buried under layers of sedimentary rocks and, under the influence of pressure and temperature, turned into coal (Raven et al., 2007; Mauseth, 2016).

Coal is a most important mineral resource that is used as fuel and raw material for the chemical industry. Its formation is a direct consequence of the evolution of vascular plants in the Carboniferous period (Yakovlev et al., 2006).

It is important to note that Carboniferous forests were not similar to modern ones. They consisted of groups that today are either extinct or represented by small relicts. Arborescent lycophytes, horsetails, and ferns are examples of archaic groups that reached prosperity but then gave way to more advanced groups (Raven et al., 2007; Mauseth, 2016).

3.10. Significance of the emergence of vascular plants for systematics and the agrosphere

The emergence of vascular plants is a key stage in the evolution of the terrestrial flora. It created the prerequisites for:

1. The formation of terrestrial ecosystems — forests, meadows, swamps.

2. An increase in biomass — vascular plants produce significantly more biomass than bryophytes.

3. The appearance of new ecological niches — vascular plants colonized diverse habitats, from humid tropics to arid deserts.

4. The evolution of seed plants — the vascular system became the basis for the further complication of plants (Judd et al., 2018; Raven et al., 2007).

For systematics and the agrosphere, understanding the evolution of vascular plants is important because:

• All cultivated plants are vascular plants. Their evolutionary history is the history of adaptations to the terrestrial environment.
• The features of vascular plants — the presence of roots, stems, leaves, and seeds — are the features that humans selected during domestication.
• Understanding evolution allows us to better understand which features are homologous and which are analogous. This is important for systematics and breeding.
• Fossil remains of vascular plants are a source of information about ancient floras that can be used to understand modern ecosystems (Judd et al., 2018; Yakovlev et al., 2006).

Conclusion

Thus, we have examined the emergence of vascular plants — a key stage in the evolution of the terrestrial flora. We established that vascular plants are characterized by the presence of xylem and phloem, dominance of the sporophyte, and the presence of true roots, stems, and leaves. We examined the most ancient groups of vascular plants — rhyniophytes, lycophytes, horsetails, and ferns — and discussed their role in the formation of Carboniferous forests and the formation of coal.

We also discussed the significance of this stage for systematics and the agrosphere. Understanding the evolution of vascular plants is necessary for understanding the systematics of cultivated plants and for developing breeding strategies.

In the next lecture we will examine the next major stage in plant evolution — the emergence of the seed, which allowed plants to become fully independent of water for reproduction and created the prerequisites for the appearance of modern agricultural crops.

4.1. The problem of reproduction in a moist environment

To understand the significance of the seed, it is necessary first to realize the problem that it solved. In all spore-bearing plants — bryophytes, lycophytes, horsetails, and ferns — sexual reproduction depends on liquid water. Their male gametes — spermatozoids — are motile and have flagella. To reach the egg cell, they must swim in water. This means that sexual reproduction is possible only under conditions of sufficient moisture (Raven et al., 2007; Mauseth, 2016).

This dependence on water imposes serious limitations on the distribution of plants. Spore-bearing plants cannot colonize arid habitats because their spermatozoids cannot reach the egg cell. Even in temperate latitudes, sexual reproduction of many spore-bearing plants is confined to moist seasons (Yakovlev et al., 2006).

In addition, in spore-bearing plants the gametophyte — the haploid generation that produces gametes — is often an independent organism that must grow in a moist environment. In ferns, the gametophyte (prothallus) is a small plate that grows on the soil surface and requires constant moisture. In lycophytes, the gametophyte may be underground and depend on symbiosis with fungi, but it still needs water for fertilization (Raven et al., 2007; Mauseth, 2016).

Thus, dependence on water for reproduction was one of the main factors limiting the distribution of spore-bearing plants. The solution to this problem became possible thanks to the appearance of the seed.

4.2. Prerequisites for the emergence of the seed: heterospory and endospory

The emergence of the seed was not a single event — it was a long process that included several successive stages. The key prerequisites were heterospory and endospory (Judd et al., 2018; Raven et al., 2007).

4.3. Formation of the seed: key innovations

The seed is a complex structure that includes several components: the embryo, stored nutrients, and the seed coat. The formation of the seed included several key innovations (Judd et al., 2018; Mauseth, 2016).

4.4. The first seed plants: gymnosperms

Gymnosperms (Gymnospermae) are a group of seed plants in which the seeds are not enclosed in an ovary (fruit). The seeds of gymnosperms are located openly on megasporophylls or on specialized structures — cones (Judd et al., 2018; Mauseth, 2016).

Gymnosperms appeared in the Late Devonian — about 365 million years ago. They reached their peak in the Mesozoic — about 250–65 million years ago — and still play an important role in the vegetation cover, especially in temperate and cold regions (Judd et al., 2018; Raven et al., 2007).

Modern gymnosperms are represented by several groups: cycads (Cycadophyta), ginkgos (Ginkgophyta), conifers (Coniferophyta), and gnetophytes (Gnetophyta). In total there are about 1,000 species of gymnosperms (Judd et al., 2018; Mauseth, 2016).

4.5. Significance of the seed for agriculture

The emergence of the seed was of colossal significance for the evolution of plants and for human civilization. The seed is a key aromorphosis that created the prerequisites for the emergence of agriculture (Fuller, 2007; Hartmann et al., 2011).

4.6. Gymnosperms and agriculture

Although gymnosperms did not become the basis of agriculture (that role fell to the angiosperms), some gymnosperms have important economic significance.

Conifers are a source of wood, which is used in construction, paper production, and furniture. Pine, spruce, larch, and fir are the most important forest-forming species (Yakovlev et al., 2006; Judd et al., 2018).

Cycads are a source of starch (sago), which is used as food in some regions. However, cycads are poisonous and require special processing (Yakovlev et al., 2006).

Ginkgo is used in medicine and as an ornamental plant. Its seeds are edible but have an unpleasant odor (Yakovlev et al., 2006).

Gnetophytes — some species are used in medicine (ephedra) and as a source of edible oil (gnetum) (Yakovlev et al., 2006).

4.7. Transition to angiosperms

Gymnosperms dominated in the Mesozoic, but in the Cretaceous period — about 130–100 million years ago — angiosperms (Angiospermae) appeared, which quickly became the dominant group. Angiosperms differ from gymnosperms in the presence of a flower and fruit, as well as double fertilization (Judd et al., 2018; Soltis et al., 2014).

The transition to angiosperms became the next major stage in plant evolution. Angiosperms created new possibilities for reproduction and dispersal, which made them the basis of modern agriculture (Judd et al., 2018; Fuller, 2007).

Conclusion

Thus, we have examined the emergence of the seed — a key stage in the evolution of land plants. We established that the seed allowed plants to become independent of water for reproduction and dispersal. The seed includes an embryo, stored nutrients, and a seed coat, and it can be in a state of dormancy, which allows it to survive unfavorable conditions.

We examined the first seed plants — the gymnosperms — and discussed their role in evolution and economic use. We also discussed the significance of the seed for agriculture: storage, transport, sowing, breeding, and nutritional value.

In the next lecture we will examine the next major stage in plant evolution — the appearance of the flower, fruit, and double fertilization, which made angiosperms the dominant group and the basis of modern crop production.

5.1. Angiosperms: key innovations

Angiosperms (Angiospermae), or flowering plants (Magnoliophyta), are the largest group of modern plants, numbering more than 250,000 species. They dominate in most terrestrial ecosystems and form the basis of modern agriculture (Judd et al., 2018; Raven et al., 2007).

Angiosperms are characterized by a number of key innovations that distinguish them from gymnosperms:

1. Presence of a flower — a specialized reproductive shoot that contains microsporophylls (stamens) and megasporophylls (carpels).

2. Presence of a carpel — a specialized leaf-like structure that surrounds the ovules and forms the ovary.

3. Double fertilization — a process in which one sperm fertilizes the egg cell, and the second fuses with the central cell, forming the endosperm.

4. Reduced female gametophyte — usually consists of eight cells (Polygonum type).

5. Reduced male gametophyte — usually consists of three cells (two sperm and a tube cell).

6. Vessels in the xylem — most angiosperms have vessels, which provide more efficient water transport.

7. Companion cells in the phloem — specialized cells that regulate the function of sieve tubes (Judd et al., 2018; Mauseth, 2016; Rudall, 2013).

These innovations formed during evolution and provided angiosperms with advantages that allowed them to become the dominant group. Let us examine each of them in more detail.

5.2. The flower: structure and origin

The flower is a specialized reproductive shoot that contains sterile and fertile organs. The sterile organs — the perianth (calyx and corolla) — perform the functions of protection and attraction of pollinators. The fertile organs — stamens (microsporophylls) and carpels (megasporophylls) — produce microspores and megaspores, respectively (Judd et al., 2018; Mauseth, 2016; Rudall, 2013).

5.3. The fruit: protection and dispersal of seeds

The fruit is the mature ovary (or ovary together with other parts of the flower), which contains seeds. The fruit performs two main functions: protection of seeds and dispersal of seeds (Judd et al., 2018; Mauseth, 2016).

5.4. Double fertilization and the endosperm

Double fertilization is a unique feature of angiosperms. Unlike gymnosperms, in which one sperm fertilizes the egg cell, in angiosperms two sperm participate in fertilization (Judd et al., 2018; Mauseth, 2016; Becker et al., 2025).

5.5. Why angiosperms became the dominant group

Angiosperms appeared in the Cretaceous period — about 130–100 million years ago — and quickly became the dominant group of the terrestrial flora. Their success is associated with a number of key innovations (Judd et al., 2018; Rudall, 2013; Soltis et al., 2014):

1. Flower and coevolution with pollinators — the flower ensures efficient pollination with the help of animals, which increases the probability of fertilization and reduces dependence on wind.

2. Fruit and seed dispersal — the fruit protects the seeds and ensures their dispersal by animals, wind, or water.

3. Double fertilization and endosperm — the endosperm ensures rapid development of the embryo and high germination energy.

4. Vessels in the xylem — vessels provide more efficient water transport, which allows angiosperms to reach large sizes and grow in more arid conditions.

5. Companion cells in the phloem — they regulate the function of sieve tubes and ensure more efficient transport of products of photosynthesis.

6. Rapid life cycle — many angiosperms are annual or biennial plants that grow and reproduce quickly. This allows them to quickly colonize new habitats and adapt to environmental changes (Judd et al., 2018; Rudall, 2013; Soltis et al., 2014).

5.6. Significance for systematics and the agrosphere

The appearance of the flower, fruit, and double fertilization is of colossal significance for systematics and the agrosphere.

5.7. Main families of angiosperms and their economic importance

Angiosperms include many families that have important economic significance. Let us consider some of them (Judd et al., 2018; Yakovlev et al., 2006):

• Grasses (Poaceae) — wheat, rice, maize, barley, oats, rye. These are the most important food crops, which provide the main part of the calories in human nutrition.
• Legumes (Fabaceae) — pea, bean, soybean, lentil, lupine. They are rich in proteins and are capable of symbiosis with nitrogen-fixing bacteria.
• Solanaceae — potato, tomato, pepper, eggplant. These are important vegetable crops.
• Cucurbits (Cucurbitaceae) — cucumber, pumpkin, watermelon, melon. These are important melon crops.
• Crucifers (Brassicaceae) — cabbage, radish, turnip, mustard, rapeseed. These are important vegetable and oilseed crops.
• Rosaceae — apple, pear, cherry, plum, raspberry, strawberry. These are important fruit and berry crops.
• Asteraceae — sunflower, lettuce, artichoke. These are important oilseed and vegetable crops.

Conclusion

Thus, we have examined the appearance of the flower, fruit, and double fertilization — the key innovations of angiosperms that made them the dominant group of the terrestrial flora. We established that the flower is a specialized reproductive shoot that ensures efficient pollination with the help of animals. The fruit is the mature ovary that protects the seeds and ensures their dispersal. Double fertilization is a unique feature of angiosperms that leads to the formation of the zygote and endosperm.

We also discussed the significance of these innovations for systematics and the agrosphere. Understanding the evolution of the flower, fruit, and double fertilization is necessary for understanding the systematics of cultivated plants and for developing breeding strategies.

In the next lecture we will examine the phylogenetic events that gave rise to modern agriculture. We will discuss the appearance of the key families — grasses, legumes, solanaceous plants, cucurbits — and the connection of evolutionary innovations with economically valuable traits.

6.1. From evolution to domestication: the general logic

Before moving on to specific families, it is important to understand the general logic of the connection between evolution and agriculture. Humans did not “create” cultivated plants from scratch — they selected those traits that arose during natural evolution and turned out to be useful for humans (Fuller, 2007; Yakovlev et al., 2006).

This means that the phylogenetic history of plants determines which traits are available for domestication. For example, if a group of plants does not produce large seeds, humans cannot domesticate it as a grain crop. If a group does not form fleshy fruits, it will not become a fruit crop. Thus, evolutionary heritage limits and directs domestication (Fuller, 2007; Judd et al., 2018).

On the other hand, domestication is also an evolutionary process. Humans create new selection conditions under which those plants that are most useful to them survive and reproduce. This leads to rapid evolutionary changes — the domestication syndrome (Fuller, 2007; Mauseth, 2016).

The domestication syndrome is a complex of traits that distinguish cultivated plants from their wild ancestors. These include:

1. Increase in the size of seeds or fruits — humans select plants with larger edible organs.

2. Loss of natural seed dispersal — cultivated plants do not “scatter” seeds but retain them on the plant until harvest.

3. Loss of seed dormancy — cultivated seeds germinate quickly and uniformly.

4. Synchronous ripening — all plants ripen at the same time, which facilitates harvesting.

5. Reduction of bitterness or toxicity — humans select plants with a lower content of protective substances.

6. Increase in productivity — cultivated plants produce more biomass or seeds (Fuller, 2007; Mauseth, 2016; Hartmann et al., 2011).

These traits arose during evolution under the action of artificial selection. Humans acted as breeders, although they did not fully realize it (Fuller, 2007; Soltis et al., 2014).

6.2. Grasses (Poaceae): the basis of food security

Grasses (Poaceae, or Gramineae) are, undoubtedly, the most important family of angiosperms from the point of view of agriculture. They include wheat, rice, maize, barley, oats, rye, sorghum, and millet — crops that provide the main part of the calories in human nutrition (Judd et al., 2018; Fuller, 2007).

6.3. Legumes (Fabaceae): a source of protein and nitrogen

Legumes (Fabaceae, or Leguminosae) are the second most important family of angiosperms. They include pea, bean, soybean, lentil, chickpea, lupine, peanut, clover, and alfalfa (Judd et al., 2018; Yakovlev et al., 2006).

6.4. Solanaceae: vegetables and medicines

Solanaceae are a family of dicots that includes potato, tomato, pepper, eggplant, tobacco, belladonna, and datura (Judd et al., 2018; Yakovlev et al., 2006).

6.5. Cucurbits (Cucurbitaceae): melon crops

Cucurbits (Cucurbitaceae) are a family of dicots that includes cucumber, pumpkin, watermelon, melon, zucchini, and pattypan squash (Judd et al., 2018; Yakovlev et al., 2006).

6.6. Other important families

Besides those listed, a number of other families of angiosperms have important economic significance (Judd et al., 2018; Yakovlev et al., 2006):

• Crucifers (Brassicaceae) — cabbage, radish, turnip, mustard, rapeseed. Important vegetable and oilseed crops.
• Rosaceae — apple, pear, cherry, plum, raspberry, strawberry. Important fruit and berry crops.
• Asteraceae — sunflower, lettuce, artichoke. Important oilseed and vegetable crops.
• Umbellifers (Apiaceae) — carrot, parsley, dill, celery, coriander. Important vegetable and spice crops.
• Alliums (Alliaceae) — onion, garlic. Important vegetable crops.
• Grape family (Vitaceae) — grape. An important fruit crop.
• Olive family (Oleaceae) — olive, ash. Olive is an important fruit crop.
• Palms (Arecaceae) — coconut palm, date palm, oil palm. Important food and technical crops (Judd et al., 2018; Yakovlev et al., 2006).

6.7. The role of polyploidy and hybridization in the evolution of cultivated plants

Polyploidy is an increase in the number of sets of chromosomes in cells. Polyploidy is widespread among plants and plays an important role in the evolution and breeding of cultivated plants (Soltis et al., 2014; Mauseth, 2016).

6.8. Connection of evolutionary innovations with economically valuable traits

Let us summarize: which evolutionary innovations became the basis of economically valuable traits?

This table shows that evolutionary heritage determines which traits are available for domestication. Understanding phylogenetic events allows us to better understand why some groups of plants became cultivated and others did not (Fuller, 2007; Judd et al., 2018; Soltis et al., 2014).

6.9. Significance for systematics and the agrosphere

Understanding the phylogenetic events that gave rise to modern agriculture is important for systematics and the agrosphere.

Conclusion

Thus, we have examined the phylogenetic events that gave rise to modern agriculture. We established that the key families of angiosperms — grasses, legumes, solanaceous plants, cucurbits, and others — arose during evolution and acquired traits that made them suitable for domestication. We discussed the role of polyploidy and hybridization in the evolution of cultivated plants and showed how evolutionary innovations are connected with economically valuable traits.

In the final lecture we will sum up the entire course and discuss why understanding evolution is necessary for systematics and breeding.

7.1. Sequence of key aromorphoses

The evolution of land plants is a sequence of key aromorphoses, each of which qualitatively changed the possibilities of plants and opened new ecological niches. Let us consider this sequence once again (Judd et al., 2018; Mauseth, 2016; Raven et al., 2007).

The first aromorphosis — the emergence onto land. This transition became possible thanks to preadaptations that formed in charophyte algae: the phragmoplast and plasmodesmata, apical growth, retention of the zygote on the parent organism, and protective coverings. The first land plants — the bryophytes — retained dependence on water for reproduction and dominance of the gametophyte. Their evolutionary limitations did not allow them to become the basis of agriculture, but they colonized the land and created the prerequisites for further evolution (Ligrone et al., 2012; Renzaglia et al., 2000; Bennici, 2008).

The second aromorphosis — the appearance of the vascular system. Xylem and phloem ensured efficient transport of water and nutrients, which allowed plants to reach large sizes, form true roots, stems, and leaves, and also to dominate the sporophyte in the life cycle. Vascular plants — lycophytes, horsetails, ferns — formed the first true forests in the Carboniferous period. Their remains became the basis for the formation of coal. The appearance of the vascular system created the prerequisites for further evolution — seed plants (Kenrick & Crane, 1997; Raven et al., 2007; Doyle, 2013).

The third aromorphosis — the emergence of the seed. The seed allowed plants to become fully independent of water for reproduction and dispersal. The seed includes an embryo, stored nutrients, and a seed coat, and can be in a state of dormancy, which allows it to survive unfavorable conditions. Gymnosperms — the first seed plants — dominated in the Mesozoic. The seed created the prerequisites for agriculture: storage, transport, sowing, breeding (Judd et al., 2018; Mauseth, 2016; Fuller, 2007).

The fourth aromorphosis — the appearance of the flower, fruit, and double fertilization. The flower ensured efficient pollination with the help of animals, the fruit — protection and dispersal of seeds, double fertilization — the formation of the endosperm, a nutritive tissue for the embryo. Angiosperms became the dominant group of the terrestrial flora and the basis of modern crop production (Judd et al., 2018; Rudall, 2013; Becker et al., 2025).

The fifth aromorphosis — polyploidy and hybridization. These genetic mechanisms ensured an increase in the size of organs, an increase in productivity, and resistance to unfavorable conditions. Many of the most important cultivated plants are polyploids (wheat, potato, cotton) or hybrids (triticale, rapeseed, strawberry). Polyploidy and hybridization became the key mechanisms of the evolution of cultivated plants (Soltis et al., 2014; Mauseth, 2016).

7.2. Each transition created new ecological possibilities

It is important to understand that each aromorphosis did not simply “improve” plants — it created new ecological possibilities that opened the path for further evolution. Let us consider this logic once again.

The emergence onto land created the possibility of using terrestrial resources: light, CO₂, and mineral substances of the soil. But it also created problems: desiccation, gravity, UV, and gas exchange. Solving these problems became the driving force of further evolution (Raven et al., 2007; Yakovlev et al., 2006).

The vascular system allowed plants to reach large sizes and colonize diverse terrestrial habitats. But it also created the possibility for the formation of complex organs — roots, stems, leaves — and for the differentiation of tissues. This opened the path for the appearance of seed plants (Kenrick & Crane, 1997; Doyle, 2013).

The seed allowed plants to become independent of water for reproduction and to disperse over long distances. But it also created the possibility for the accumulation of stored nutrients and for dormancy. This opened the path for the appearance of angiosperms (Judd et al., 2018; Mauseth, 2016).

The flower and fruit allowed angiosperms to use animals for pollination and seed dispersal. But they also created the possibility for coevolution — the mutual evolutionary influence of flowers and pollinators, fruits and dispersers. This led to the enormous diversity of angiosperms (Judd et al., 2018; Rudall, 2013).

Polyploidy and hybridization allowed cultivated plants to acquire new traits and adapt to new conditions. But they also created the possibility for rapid evolution under the action of artificial selection. This led to the appearance of modern varieties and crops (Soltis et al., 2014; Fuller, 2007).

Thus, the evolution of land plants is not simply a sequence of random changes. It is a regular process in which each aromorphosis created new possibilities and opened the path for the next stage.

7.3. Why understanding evolution is necessary for systematics

Systematics is the science of the diversity of organisms and their classification. Modern systematics is built on the phylogenetic principle: classification must reflect the evolutionary relationships between organisms (Judd et al., 2018; Yakovlev et al., 2006).

Understanding evolution is necessary for systematics for several reasons.

First, phylogenetic relationships determine which groups are monophyletic (descend from a common ancestor and include all of its descendants), and which are paraphyletic (include not all descendants of a common ancestor) or polyphyletic (descend from different ancestors). For example, bryophytes are a paraphyletic group, and angiosperms are monophyletic. Understanding this makes it possible to build a natural classification (Judd et al., 2018; Renzaglia et al., 2000).

Second, understanding evolution makes it possible to distinguish homologous and analogous traits. Homologous traits are traits inherited from a common ancestor. Analogous traits are traits that arose independently in different groups. For example, the leaves of lycophytes (microphylls) and the leaves of ferns (megaphylls) are analogous, not homologous, organs. Understanding this makes it possible to correctly interpret traits and build a classification (Tomescu, 2009; Kenrick & Crane, 1997).

Third, understanding evolution makes it possible to predict which traits may be present in still unstudied species. For example, if we know that a family is characterized by a certain type of fruit, we can expect that new species of this family will have the same type of fruit. This is important for the identification and classification of plants (Judd et al., 2018).

Fourth, understanding evolution makes it possible to understand the direction and rate of evolutionary changes. For example, we know that the loss of natural seed dispersal in grasses occurred more slowly than the increase in seed size. This knowledge helps interpret archaeobotanical data and understand the processes of domestication (Fuller, 2007).

7.4. Why understanding evolution is necessary for breeding

Breeding is the science of creating new varieties of cultivated plants. Modern breeding is built on genetic and evolutionary principles (Soltis et al., 2014; Fuller, 2007).

Understanding evolution is necessary for breeding for several reasons.

First, understanding evolution makes it possible to identify the wild relatives of cultivated plants. Wild relatives are a source of genes for resistance to diseases, drought, and cold. For example, wild species of wheat are a source of genes for resistance to rust. Understanding phylogenetic relationships makes it possible to find these relatives and use them in breeding (Judd et al., 2018; Soltis et al., 2014).

Second, understanding evolution makes it possible to understand the genetic mechanisms underlying economically valuable traits. For example, understanding that polyploidy leads to an increase in the size of cells and organs makes it possible to use polyploidization to create new varieties with large fruits (Soltis et al., 2014; Mauseth, 2016).

Third, understanding evolution makes it possible to predict the consequences of breeding decisions. For example, if we select plants with large seeds, we can expect that this will lead to a decrease in the number of seeds or to a decrease in resistance to diseases. Understanding evolutionary trade-offs makes it possible to avoid undesirable consequences (Fuller, 2007; Soltis et al., 2014).

Fourth, understanding evolution makes it possible to use evolutionary mechanisms to create new varieties. For example, hybridization makes it possible to combine valuable traits of different species, and polyploidy — to increase productivity. Understanding these mechanisms makes it possible to purposefully create new varieties (Soltis et al., 2014; Yakovlev et al., 2006).

7.5. The evolutionary tree of plants and the agrosphere: the final picture

Let us summarize. The evolutionary tree of plants is a sequence of key aromorphoses, each of which created new ecological possibilities and prerequisites for economic use. We can represent this sequence in the form of a scheme:

This scheme shows that evolutionary heritage determines which traits are available for domestication. Understanding this heritage allows us to better understand why some groups of plants became cultivated and others did not (Fuller, 2007; Judd et al., 2018; Soltis et al., 2014).