Brassicaceae, Malvaceae, and Amaranthaceae

1.1. General characterization of the role of the three families in crop production

Crop production is based on a limited number of families that provide humanity with food, feed, fiber, and industrial raw materials. Brassicaceae, Malvaceae, and Amaranthaceae occupy a special place in this series because they include both ancient and relatively recently domesticated species, demonstrating a wide spectrum of economic uses (Judd et al., 2018).

Brassicaceae is one of the largest families of flowering plants, comprising about 338 genera and more than 3,700 species (Al-Shehbaz et al., 2006; Beilstein et al., 2008). The economic importance of this family is difficult to overestimate. It gives us:

• Vegetable crops: cabbage, broccoli, cauliflower, Brussels sprouts, kohlrabi, turnip, radish, black radish, horseradish, salad mustard.
• Oilseed crops: rapeseed, turnip rape, mustard (white, black, brown).
• Forage crops: fodder turnip, fodder cabbage, rapeseed for green fodder.
• Condiments and medicinal plants: mustard, horseradish, garden cress.
• Model biological organism: thale cress (Arabidopsis thaliana), widely used in genetics and molecular biology (Gupta, 2009).

Malvaceae in the broad sense (including the former Bombacaceae, Sterculiaceae, and Tiliaceae) comprises about 243 genera and more than 4,300 species (Bayer and Kubitzki, 2003). This family provides the world with:

• Fiber crops: cotton (Gossypium spp.) — the most important natural fiber crop.
• Food crops: cacao (Theobroma cacao), okra (Abelmoschus esculentus), durian (Durio zibethinus), cola (Cola spp.).
• Ornamental plants: hibiscus, mallow, hollyhock, linden.
• Timber crops: linden, some Sterculiaceae and Bombacaceae.

Amaranthaceae (including the former family Chenopodiaceae) comprises about 169 genera and more than 2,360 species (Kadereit et al., 2003; Judd et al., 2018). Economic importance:

• Sugar crop: sugar beet (Beta vulgaris subsp. vulgaris var. altissima) — the only sugar crop of the temperate zone, providing about 20–25% of world sugar (Draycott, 2006).
• Vegetable crops: table beet, Swiss chard, spinach (Spinacia oleracea).
• Grain pseudocereals: quinoa (Chenopodium quinoa), amaranth (Amaranthus spp.) — ancient crops of the Andes and Mexico with a unique amino acid composition (Bhargava and Srivastava, 2013; Paredes-López, 1994).
• Forage crops: fodder beet, amaranth for green mass.
• Weeds: white goosefoot (Chenopodium album), redroot pigweed (Amaranthus retroflexus) — noxious weeds, but at the same time genetic resources for breeding.

The diversity of life forms in these three families is impressive: from annual herbs (radish, spinach, amaranth) to perennial trees (linden, cacao, some Sterculiaceae). Ecological niches are also broad: from Arctic and temperate zones (cabbage, beet) to the tropics (cacao, cotton) and the high Andes (quinoa). Many species are xerophytes (amaranth, some mallows) or halophytes (beet, spinach), which makes them promising for cultivation under climate change (Bhargava and Srivastava, 2013; FAO, 2011).

1.2. Brassicaceae: vegetable, oilseed, and forage crops

The family Brassicaceae (order Brassicales, clade Malvids, group Rosids) is one of the most economically significant families of the temperate zone. Its center of origin is the Mediterranean and Southwest Asia (Gómez-Campo and Prakash, 1999). The key genus is Brassica, which includes the famous “Triangle of U” (U, 1935):

• B. oleracea (cabbage, broccoli, cauliflower, kohlrabi, Brussels sprouts) — diploid, 2n=18, CC genome.
• B. rapa (turnip, fodder turnip, Chinese cabbage, napa cabbage) — diploid, 2n=20, AA genome.
• B. nigra (black mustard) — diploid, 2n=16, BB genome.
• Allotetraploids: B. napus (rapeseed, rutabaga) — AACC, 2n=38; B. juncea (brown mustard) — AABB, 2n=36; B. carinata (Ethiopian mustard) — BBCC, 2n=34.

This triangle is a classic example of how knowledge of phylogeny and cytogenetics allows prediction of crossability and the creation of new crops. For example, rapeseed (B. napus) arose in nature as a spontaneous allotetraploid and was later domesticated and became a major oilseed crop (Gupta, 2009).

Other key genera:

• Raphanus (radish, black radish, daikon) — root crops.
• Sinapis (white mustard) — oilseed and condiment.
• Armoracia (horseradish) — spice-flavor crop.
• Arabidopsis — model organism, but not an agricultural crop.

Vegetable crops of Brassicaceae occupy huge areas: cabbage alone was cultivated on 3.2 million ha in 129 countries in 2005 (Prohens and Nuez, 2008). Oilseed crops (rapeseed, mustard) provide food and industrial oil, as well as biodiesel. Forage crops (fodder turnip, fodder cabbage) are used in animal husbandry. In addition, many species are sources of glucosinolates, which have anticarcinogenic properties (Cartea and Ordás, 2008).

1.3. Malvaceae: fiber, food, and ornamental plants

The family Malvaceae (order Malvales, clade Malvids, group Rosids) in its modern expanded circumscription includes four former families: Malvaceae s.str., Bombacaceae, Sterculiaceae, and Tiliaceae (Bayer and Kubitzki, 2003; Judd and Manchester, 1997). This is one of the clearest examples of how molecular phylogenetic data changed classification: what was previously considered four independent families turned out to be a single monophyletic group united by common characters (stellate hairs, mucilage cells, stratified phloem, palmate venation, valvate calyx, and trichomal nectaries).

The most important genus is Gossypium (cotton). It is the number one fiber crop in the world. Cultivated cotton species are divided into two groups:

• Diploid (2n=26): G. herbaceum (Asiatic cotton), G. arboreum (tree cotton) — Old World.
• Tetraploid (2n=52): G. hirsutum (Upland cotton, 90% of world production), G. barbadense (Egyptian cotton, Pima) — New World, arose as a result of natural hybridization between Asiatic and American diploid species (Kubitzki, 2003).

Polyploidy played a key role in cotton evolution: tetraploid species have longer and stronger fiber, which made them the basis of the modern textile industry.

Other important genera:

• Theobroma cacao (cacao) — source of chocolate, one of the most important food products of the tropics. Belongs to the former Sterculiaceae.
• Abelmoschus esculentus (okra) — vegetable crop.
• Hibiscus (hibiscus, kenaf, roselle) — ornamental, fiber, medicinal.
• Tilia (linden) — timber, honey, ornamental crop.
• Alcea (hollyhock), Malva (mallow) — ornamental and medicinal.
• Cola (cola) — source of caffeine, tonic.

The economic importance of Malvaceae is multifaceted: fiber (cotton, kenaf, jute from Corchorus, which also belongs to the mallows in the broad sense), food products (cacao, okra, durian), timber (linden, some Sterculiaceae), ornamental plants (hibiscus, hollyhock), medicinal plants (mallow, marshmallow). Many species are important components of tropical agroecosystems.

1.4. Amaranthaceae: sugar crop, vegetables, and grain pseudocereals

The family Amaranthaceae (order Caryophyllales, clade Superasterids) in its modern circumscription includes the former family Chenopodiaceae (Kadereit et al., 2003; Judd et al., 2018). This is an example of how molecular data united two morphologically different groups: amaranths (with glomerulate inflorescences and dry nut-like fruits) and chenopods (with small inconspicuous flowers, often wind-pollinated). The unification is based on common characters: presence of betalains (red and yellow pigments), ring or spiral cambia, curved embryo, perisperm in the seed.

The most important genus is Beta (beet). Cultivated beet (B. vulgaris) includes several groups:

• Sugar beet (var. altissima) — biennial plant, root crop with high sucrose content (16–20%). It provides about 20–25% of world sugar (Draycott, 2006).
• Fodder beet (var. crassa) — large root crops for livestock.
• Table beet (var. conditiva) — vegetable crop with red roots.
• Leaf beet, or Swiss chard (var. cicla) — leafy vegetable.

Beet is the only sugar crop of the temperate zone competing with tropical sugarcane. Its wild ancestor is Beta maritima (sea beet), growing along the shores of the Mediterranean and Black Seas (Biancardi et al., 2012). Genetic resources of wild beet are actively used in breeding for resistance to diseases (nematodes, Cercospora leaf spot, rhizomania).

Another important genus is Spinacia (spinach). S. oleracea is a vegetable crop rich in iron and vitamins, but containing oxalates.

The genus Chenopodium (goosefoot) includes quinoa (C. quinoa) — an ancient grain crop of the Andes with a unique amino acid composition (Bhargava and Srivastava, 2013; FAO, 2011). Quinoa contains all essential amino acids, including lysine, and is gluten-free. This makes it a promising crop for food security. Other species include white goosefoot (C. album) — a weed, but also an edible plant.

The genus Amaranthus (amaranth) includes grain and vegetable crops. A. hypochondriacus, A. cruentus, A. caudatus are grain amaranths, producing small seeds with high protein content (15–18%), lysine, and squalene. A. tricolor is vegetable amaranth. Amaranth is a C4 plant, resistant to drought and high temperatures, which makes it promising under climate change (Paredes-López, 1994).

Forage importance: fodder beet, amaranth for green mass. Weeds: goosefoot, pigweed — noxious weeds, but at the same time genetic resources (resistance to herbicides, drought).

1.5. Comparative analysis and significance for the agronomist

Thus, the three families demonstrate a wide spectrum of economic uses:

• Brassicaceae — vegetables, oilseeds, forage, condiments, model organism.
• Malvaceae — fiber, food, ornamental, timber.
• Amaranthaceae — sugar crop, vegetables, grain pseudocereals, forage, weeds.

Knowledge of the systematics of these families is necessary for the agronomist for several reasons. First, it allows prediction of plant properties: for example, all Brassicaceae contain glucosinolates, which determine their taste, nutritional value, and protective functions. Second, phylogenetic relationships indicate potential sources of genes for resistance to diseases and pests. For example, resistance to clubroot (Plasmodiophora brassicae) in brassicas is often found in wild relatives from the genus Brassica and closely related genera (Prohens and Nuez, 2008). Nematode resistance in beet is found in wild Beta maritima (Biancardi et al., 2012). Third, understanding evolutionary pathways (polyploidy, hybridization) helps breeders create new forms, as happened with Brassica allotetraploids or tetraploid cottons.

2.1. Phylogenetic position and monophyly

The family Brassicaceae, together with related families (Capparaceae, Cleomaceae, Resedaceae, etc.), forms the order Brassicales. The monophyly of Brassicales is reliably confirmed by molecular phylogenetic data (Judd et al., 2018). The key synapomorphy of the order is the presence of glucosinolates (mustard oils) — sulfur-containing secondary metabolites that, when tissues are damaged, are hydrolyzed by the enzyme myrosinase to release pungent isothiocyanates. These compounds are responsible for the characteristic pungent taste and odor of mustard, horseradish, radish, and cabbage.

Within the order, Brassicaceae occupy a rather isolated position. Molecular data show that the family is monophyletic and clearly delimited from the closely related Capparaceae and Cleomaceae. The main morphological synapomorphies of Brassicaceae are:

• Flowers usually bisexual, actinomorphic, with a double perianth.
• Calyx of 4 sepals, corolla of 4 petals arranged crosswise (hence the name “crucifers”).
• Androecium of 6 stamens, of which 4 are long and 2 short (tetradynamous).
• Gynoecium of 2 fused carpels, ovary superior, with parietal placentation.
• Fruit a silique or silicula, opening by two valves, with a false septum (replum) between them.
• Seeds without endosperm, with a curved embryo.

These characters together make the family easily recognizable (Gupta, 2009). However, within the family there is considerable morphological diversity, especially in fruit structure, which is associated with adaptations to various seed dispersal mechanisms.

2.2. Morphological features and adaptations

Brassicaceae are predominantly herbaceous plants, annual, biennial, or perennial. Among them are subshrubs and shrubs (for example, some species of Brassica and Sinapis), but trees are absent. Leaves alternate, simple, often pinnately or palmately lobed, without stipules. Characteristic is the presence in tissues of myrosin cells containing the enzyme myrosinase, and idioblasts with glucosinolates.

Flowers are gathered in racemose or corymbose inflorescences. Pollination is predominantly entomophilous (bees, flies, butterflies), but in some species self-pollination or cleistogamy is observed. Many Brassicaceae are characterized by sporophytic self-incompatibility controlled by a single S locus with many alleles. This mechanism ensures outcrossing and maintains a high level of genetic diversity in populations (Prohens and Nuez, 2008).

Fruits of Brassicaceae are extremely diverse and have important taxonomic significance. Main types:

• Silique — long, opening by two valves, with seeds attached to the septum (e.g., cabbage, rapeseed, mustard).
• Silicula — short, often rounded or heart-shaped (e.g., shepherd’s purse).
• Nutlet — indehiscent one-seeded fruit (in some species).
• Segmented silique — breaking into segments (in radish, black radish).

Seeds are usually small, rich in oil (up to 40–50% in oilseed forms) and protein. Embryo curved, radicle directed toward the hilum. Endosperm absent or represented by one cell layer.

2.3. Key genera and the “Triangle of U”

The central place in the economic systematics of Brassicaceae is occupied by the genus Brassica L. This genus includes about 39 species, among which are the most important cultivated plants. In 1935, the Japanese cytogeneticist Nagaharu U (U, 1935) established the phylogenetic relationships between the six main cultivated species of Brassica, combining them into the famous “Triangle of U” (Fig. 1).

Diploid species:

• B. oleracea L. (2n = 18, CC genome) — cabbage, broccoli, cauliflower, Brussels sprouts, kohlrabi, leaf cabbage.
• B. rapa L. (2n = 20, AA genome) — turnip, fodder turnip, Chinese cabbage, napa cabbage, rapeseed (some forms).
• B. nigra (L.) Koch (2n = 16, BB genome) — black mustard.

Allotetraploid species (natural hybrids):

• B. napus L. (2n = 38, AACC) — rapeseed, rutabaga. Originated from crossing B. oleracea × B. rapa.
• B. juncea (L.) Czern. (2n = 36, AABB) — brown mustard, Indian mustard. Originated from B. rapa × B. nigra.
• B. carinata A. Braun (2n = 34, BBCC) — Ethiopian mustard. Originated from B. nigra × B. oleracea.

This triangle is a classic example of how knowledge of cytogenetics and phylogeny allows prediction of crossability and the creation of new forms. For example, rapeseed (B. napus) arose in nature spontaneously and was later domesticated and became a major oilseed crop of the temperate zone. Triploid and tetraploid hybrids are widely used in breeding for transferring resistance genes and improving quality (Gupta, 2009).

Other important genera of Brassicaceae:

• Raphanus L. — radish (R. sativus), black radish, daikon. Root crops rich in vitamins and minerals.
• Sinapis L. — white mustard (S. alba), black mustard (S. nigra). Oilseed and spice-flavor plants.
• Armoracia Gaertn. — horseradish (A. rusticana). Spice-flavor crop.
• Arabidopsis Heynh. — thale cress (A. thaliana). Model object of genetics, molecular biology, and plant physiology. The complete genome was sequenced in 2000.
• Lepidium L. — garden cress (L. sativum). Salad crop.
• Capsella Medik. — shepherd’s purse (C. bursa-pastoris). Weed and medicinal plant.
• Eruca Mill. — arugula (E. vesicaria subsp. sativa). Salad crop.

2.4. Important cultivated species and their uses

Vegetable crops. Cabbage (B. oleracea) is one of the oldest vegetable crops. Depending on which organ is formed for food, several cultivar groups are distinguished (Prohens and Nuez, 2008):

• Acephala — leaf cabbage, kale, fodder cabbage.
• Capitata — headed cabbage (white cabbage, red cabbage).
• Sabauda — Savoy cabbage.
• Gemmifera — Brussels sprouts.
• Gongylodes — kohlrabi.
• Botrytis — cauliflower.
• Italica — broccoli.
• Alboglabra — Chinese broccoli (gai lan).

Napa cabbage (B. rapa subsp. pekinensis) and pak choi (B. rapa subsp. chinensis) are important vegetables in East Asia. Turnip (B. rapa subsp. rapa) and fodder turnip (B. rapa subsp. rapifera) are root crops of the temperate zone.

Radish (Raphanus sativus) is a popular vegetable crop rich in vitamin C, anthocyanins, and glucosinolates. Black radish (R. sativus var. niger) and daikon (R. sativus var. longipinnatus) are also widely cultivated.

Oilseed crops. Rapeseed (B. napus) is the third most important oilseed crop in the world after oil palm and soybean. Its oil is used as food and industrial oil (biodiesel, lubricants). Mustard (Sinapis alba, S. nigra, B. juncea) is a source of mustard oil and condiment. Camelina (Camelina sativa) is a promising oilseed crop with a high content of omega-3 fatty acids (Gupta, 2009; Gupta, 2009, ch. 17).

Forage crops. Fodder turnip, fodder cabbage, rapeseed for green fodder, rutabaga (B. napus subsp. rapifera) are important forage plants for livestock.

Spice-flavor and medicinal. Mustard, horseradish, garden cress, arugula are sources of pungent condiments. Many species are used in folk medicine as antiseptic, anti-inflammatory, and expectorant remedies.

Ornamental. Matthiola (Matthiola), sweet alyssum (Lobularia), candytuft (Iberis), dame’s rocket (Hesperis) are popular garden plants.

2.5. Wild relatives and genetic resources

Wild relatives of cultivated Brassicaceae grow mainly in the Mediterranean, Southwest Asia, and Europe. Many of them are valuable sources of genes for resistance to diseases and pests, as well as adaptation to abiotic stresses (Gupta, 2009, ch. 3).

For example, wild cabbage B. oleracea occurs on the Atlantic coast of Europe (from Spain to Great Britain). It represents the ancestral form for all cultivated forms of cabbage (Snogerup, 1980; Hodgkin, 1995). Wild species of Brassica and closely related genera (Diplotaxis, Erucastrum, Sinapis) possess resistance to clubroot (Plasmodiophora brassicae), black rot (Xanthomonas campestris), downy mildew, nematodes, and other pathogens. These traits are actively used in breeding (Prohens and Nuez, 2008).

Genetic resources of Brassicaceae are conserved in major gene banks worldwide: the International Plant Genetic Resources Institute (IPGRI, now Bioversity International), the US National Plant Germplasm System (NPGS), the European Brassica Database (Bras-EDB), the N.I. Vavilov All-Russian Institute of Plant Genetic Resources (VIR), etc. (Prohens and Nuez, 2008). The most important task is conservation of intraspecific diversity and wild populations, which may be lost due to climate change and habitat destruction.

3.1. Phylogenetic position and expanded circumscription of the family

For a long time, Malvaceae was treated as a narrow family including only herbs and shrubs with characteristic palmate leaves and fused stamens (e.g., mallow, hollyhock, hibiscus). However, molecular phylogenetic studies of the late 20th and early 21st centuries showed that four traditional families — Malvaceae s.str., Bombacaceae (baobab family), Sterculiaceae (sterculia family), and Tiliaceae (linden family) — form a single monophyletic group (Judd and Manchester, 1997; Bayer et al., 1999; Alverson et al., 1999). As a result, in modern taxonomy they are united into one expanded family Malvaceae sensu lato (Bayer and Kubitzki, 2003; Judd et al., 2018).

The monophyly of the expanded family is confirmed both by molecular data (sequences of rbcL, ndhF, ITS, etc.) and by morphological synapomorphies:

• stellate hairs;
• mucilage cells, canals, and cavities in all tissues;
• stratified phloem with hard and soft layers and triangular primary rays;
• palmate leaf venation;
• valvate calyx (sepals joined in bud);
• trichomal nectaries (nectar-bearing hairs), usually located on the inner side of sepals;
• characteristic structure of anthers and pollen grains (Bayer and Kubitzki, 2003; Judd et al., 2018).

The order Malvales, also including Bixaceae, Cistaceae, Dipterocarpaceae, Thymelaeaceae, and other families, is monophyletic and characterized by mucilage cells, stellate hairs, a valvate calyx, and cyclopropanoid fatty acids (Judd et al., 2018). Within the order, Malvaceae occupy a central position, divided into nine subfamilies: Byttnerioideae, Grewioideae, Tilioideae, Brownlowioideae, Helicteroideae, Sterculioideae, Dombeyoideae, Bombacoideae, and Malvoideae (Bayer and Kubitzki, 2003; Judd et al., 2018). This division reflects both phylogenetic relationships and morphological diversity, which previously served as the basis for separating individual families.

3.2. Morphological features and adaptations

Malvaceae are trees, shrubs, lianas, and herbs. Among them are giant trees (baobab Adansonia digitata, kapok Ceiba pentandra), epiphytes, herbs, and even succulents. Leaves alternate, simple, often palmately lobed or palmately compound, with stipules. Stellate hairs are characteristic and may be glandular, as are lush crowns and large bright flowers.

Flowers usually bisexual, actinomorphic (less often zygomorphic), with a double perianth. Calyx of 5 (less often 3–4) sepals, often fused into a tube; corolla of 5 petals, free or fused with the bases of the stamen filaments. A characteristic feature is the presence of an epicalyx of 3 or more bracts, especially in Malvoideae. Androecium consists of 5 or numerous stamens, often fused into a tube (column) surrounding the style. Gynoecium of 2–5 (less often 10–40) carpels, ovary superior, with axile placentation. Fruits diverse: capsules, nuts, berries, drupes, follicles, often with hairs (cotton) or wings.

Pollination is predominantly entomophilous (bees, flies, butterflies, beetles), but in some tropical genera (baobab, kapok, durian) it is chiropterophilous (bats) or ornithophilous (birds). Malvaceae are characterized by sporophytic self-incompatibility ensuring outcrossing (Bayer and Kubitzki, 2003).

Fruits and seeds of Malvaceae demonstrate a wide range of adaptations for dispersal: from samaras in Tilia and Pterospermum to fibrous seeds in Gossypium (cotton) and fleshy fruits in Theobroma (cacao). Seeds often contain endosperm or perisperm, embryo curved or straight.

3.3. Key genera and important cultivated species

3.4. Economic importance

Fiber. Cotton (Gossypium) is the main fiber crop of the world. Cotton fiber consists of almost pure cellulose, has high strength, hygroscopicity, and dyeability. In addition to cotton, fiber is produced by kenaf (Hibiscus cannabinus), jute (Corchorus spp., subfamily Grewioideae), and kapok (Ceiba pentandra). These fibers are used for producing fabrics, ropes, burlap, and stuffing materials.

Food crops. Cacao (Theobroma cacao) is the basis of the chocolate industry. Okra (Abelmoschus esculentus) is a vegetable crop. Durian (Durio zibethinus) is a popular fruit of Southeast Asia. Cola (Cola spp.) is a source of tonic drinks. Linden (Tilia) is a honey plant.

Timber crops. Linden (Tilia) produces soft wood used in carpentry, for making musical instruments, pencils, and plywood. Balsa (Ochroma pyramidale) is the lightest wood, used in modeling, aircraft construction, and life jackets. Kapok (Ceiba) and other Bombacoideae provide wood and fiber.

Ornamental plants. Hibiscus (Hibiscus), hollyhock (Alcea), mallow (Malva), lavatera (Lavatera), linden (Tilia) are popular ornamental plants in gardens and parks. Large bright flowers of hibiscus and hollyhock are especially valued.

Medicinal plants. Mallow (Malva), marshmallow (Althaea officinalis) are sources of mucilages used as demulcent and anti-inflammatory agents. Hibiscus (karkade) is a source of anthocyanins with antioxidant properties. Linden is a diaphoretic and anti-inflammatory agent.

3.5. Genetic resources and breeding

Genetic resources of Malvaceae are vast but unevenly studied. Most important for breeding are wild relatives of cotton possessing resistance to diseases and pests, as well as to abiotic stresses (drought, salinity). Wild species of Gossypium grow in arid regions of Australia, Africa, and America. Their genomes (A, B, C, D, E, F, G, K) represent a valuable reserve for introgression of genes into cultivated tetraploids (Bayer and Kubitzki, 2003).

For cacao (Theobroma cacao), wild populations from Amazonia are important, possessing resistance to diseases (e.g., witches’ broom — Moniliophthora perniciosa). Genetic resources of okra, hibiscus, and linden are also conserved in gene banks, although their study is less advanced.

Modern breeding of Malvaceae uses marker-assisted selection (MAS), genome editing (CRISPR/Cas9), as well as traditional hybridization and polyploidization. For example, for cotton, genetic maps have been developed that allow identification of QTLs controlling fiber quality, disease and pest resistance (Judd et al., 2018).

4.1. Phylogenetic position and expanded circumscription of the family

For a long time, Amaranthaceae and Chenopodiaceae (goosefoot family) were regarded as two separate, although closely related, families. Molecular phylogenetic studies of the late 20th and early 21st centuries showed that Chenopodiaceae are paraphyletic relative to Amaranthaceae, and in 1998 in the APG system they were united into a single expanded family Amaranthaceae sensu lato (APG, 1998; Kadereit et al., 2003; Judd et al., 2018). This unification is confirmed both by molecular data (sequences of the genes rbcL, matK, ITS, ndhF, etc.) and by a number of morphological and biochemical synapomorphies:

• the presence of betalains (red and yellow pigments), rather than anthocyanins;
• ring-shaped or spiral cambia (anomalous secondary growth);
• curved or spirally coiled embryo;
• perisperm in the seed (storage tissue developing from the nucellus);
• small, inconspicuous flowers, often wind-pollinated;
• characteristic structure of pollen grains (polyporate, with spiny or wrinkled surface).

The order Caryophyllales, which also includes Cactaceae, Caryophyllaceae, Phytolaccaceae, Nyctaginaceae, Aizoaceae, Portulacaceae, Droseraceae, Polygonaceae, and others, is monophyletic and is characterized by the presence of betalains, free-central or basal placentation, a curved embryo, and perisperm (Judd et al., 2018). Within the order, Amaranthaceae occupy a central position, splitting into several subfamilies, the most important of which are Amaranthoideae, Chenopodioideae, Betoideae, Spinacioideae, Corispermoideae, Polycnemoideae, and others (Kadereit et al., 2003; Judd et al., 2018). This division reflects both phylogenetic relationships and morphological diversity, which previously served as the basis for separating individual families.

4.2. Morphological features and adaptations

Amaranthaceae are predominantly herbaceous plants, annual or perennial, less often subshrubs, shrubs, and small trees. Among them there are succulents (some species of Suaeda, Salicornia), halophytes (salt-tolerant plants, for example, Salicornia, Atriplex), xerophytes (drought-tolerant, for example, Amaranthus, Salsola), and even aquatic plants. Leaves alternate or opposite, simple, often fleshy, without stipules. The presence of mucilage cells and idioblasts with calcium oxalate is characteristic.

Flowers usually small, inconspicuous, bisexual or unisexual (plants monoecious or dioecious), gathered in compound inflorescences — glomerules, spikes, panicles. Perianth simple, calyx-like, of 3–5 (less often 1–2 or 6) free or fused tepals, often membranous or fleshy. Androecium consists of 1–5 (less often more) stamens opposite the perianth tepals. Gynoecium of 2–5 carpels, ovary superior or semi-inferior, with basal, free-central, or axile placentation. Fruits diverse: nutlets, achenes, capsules, berries, often fused with the perianth. Seeds small, with perisperm and a curved embryo.

Pollination predominantly wind (anemophily), but in some genera (for example, Amaranthus, Celosia) — entomophilous. Many Amaranthaceae are characterized by high seed productivity (up to 100,000 seeds per plant in white goosefoot), which makes them successful colonizers of disturbed habitats. Many species are C4 plants, which ensures high photosynthetic efficiency under conditions of high temperatures and drought (for example, Amaranthus, Salsola, Atriplex).

4.3. Key genera and most important cultivated species

4.4. Economic importance

Sugar crop. Sugar beet (Beta vulgaris var. altissima) is the only sugar crop of the temperate zone, providing about 20–25% of world sugar. Major producers: France, Germany, the USA, Russia, Ukraine, Poland, Turkey, and China (Draycott, 2006).

Vegetable crops. Garden beet, chard, spinach, quinoa (as a vegetable green), vegetable amaranth, and salicornia are important vegetable crops rich in vitamins, minerals, and antioxidants.

Grain pseudocereals. Quinoa and amaranth are ancient grain crops possessing a unique amino acid composition and high nutritional value. They are promising for the production of gluten-free products, baby food, and dietary nutrition (Bhargava and Srivastava, 2013; Paredes-López, 1994; FAO, 2011).

Forage crops. Fodder beet, amaranth for green mass, saltbush, and saltwort are important forage plants, especially in arid and saline areas.

Medicinal plants. Many species are used in folk medicine: goosefoot, amaranth, beet, spinach, and glasswort.

Ornamental plants. Celosia, gomphrena, amaranth, kochia, iresine, and alternanthera are popular ornamental plants.

Weed plants. White goosefoot, redroot pigweed (Amaranthus retroflexus), and saltwort (Salsola spp.) are noxious weeds that reduce the yield of cultivated plants. However, they are also genetic resources for breeding (resistance to herbicides, drought, and salinity).

4.5. Genetic resources and centers of origin

Centers of origin of the most important cultivated Amaranthaceae:

• Beet — Mediterranean, Western Asia. Wild ancestor — Beta maritima (Biancardi et al., 2012).
• Spinach — Western and Central Asia.
• Quinoa — the Andes (Peru, Bolivia, Ecuador, Chile, Argentina). Center of diversity — the Lake Titicaca region (Bhargava and Srivastava, 2013; FAO, 2011).
• Amaranth — Mexico, Central America, the Andes. Centers of diversity — Mexico, Guatemala, Peru, Bolivia (Paredes-López, 1994).

Genetic resources of Amaranthaceae are conserved in major gene banks of the world: in the International Potato Center (CIP, Peru), in the US National Plant Germplasm System (NPGS), in the European database (EURISCO), in the All-Russian Institute of Plant Genetic Resources (VIR), etc. Particular attention is paid to the conservation of wild relatives of cultivated plants possessing resistance to diseases, pests, and abiotic stresses.

5.1. Phylogeny and identification of taxa

The first practical application of phylogeny is accurate identification of species, varieties, and hybrids. Traditional identification by morphological characters is often difficult because of phenotypic plasticity, convergent evolution, and the presence of cryptic species (Judd et al., 2018). Molecular markers (RAPD, AFLP, SSR, SNP, ITS, rbcL, matK, etc.) make it possible to construct phylogenetic trees and unambiguously determine taxa.

Brassicaceae. The famous “U triangle” (U, 1935) is a classic example of how cytogenetics and phylogeny ordered the identification of six major cultivated species of Brassica. Molecular data confirmed that B. napus (AACC), B. juncea (AABB), and B. carinata (BBCC) are allotetraploids that arose from natural hybridizations between diploid species (Gupta, 2009, ch. 2). This allows breeders to predict crossability and use synthetic amphiploids to transfer genes. In addition, DNA barcoding (for example, by the matK gene) helps distinguish closely related species of Brassica, Sinapis, Diplotaxis, and Erucastrum, which is important for phytosanitary control and identification of weed plants (Warwick and Sauder, 2005).

Malvaceae. Molecular phylogenetic studies of the late 20th century showed that four traditional families — Malvaceae s.str., Bombacaceae, Sterculiaceae, and Tiliaceae — form a single monophyletic group (Judd and Manchester, 1997; Bayer et al., 1999; Alverson et al., 1999). This led to their unification into the expanded family Malvaceae sensu lato (Bayer and Kubitzki, 2003). Such reclassification is important for identification: for example, cacao (Theobroma cacao), previously assigned to Sterculiaceae, is now considered Malvaceae (subfamily Byttnerioideae), and baobab (Adansonia) — Malvaceae (Bombacoideae). Molecular markers make it possible to accurately determine species of Gossypium, Hibiscus, Tilia, and their hybrids.

Amaranthaceae. The unification of Amaranthaceae and Chenopodiaceae into one family (APG, 1998; Kadereit et al., 2003) is also based on molecular data. This is important for identification of quinoa (Chenopodium quinoa), white goosefoot (C. album), amaranth (Amaranthus spp.), and beet (Beta vulgaris). Molecular markers make it possible to distinguish closely related species of Chenopodium and Amaranthus, as well as to detect hybrids and polyploids (Bhargava and Srivastava, 2013; Paredes-López, 1994).

Thus, phylogeny provides a reliable basis for identification of taxa, which is necessary for breeding, seed production, quarantine, and conservation of biodiversity.

5.2. Phylogeny as a basis for searching for donors of economically valuable traits

One of the main practical applications of phylogeny is the search for wild relatives possessing resistance to diseases, pests, and abiotic stresses. The closer a wild species is phylogenetically to a cultivated one, the higher the probability of successful hybridization and gene transfer (Harlan and de Wet, 1971). Let us consider specific examples.

5.3. Phylogeny and understanding genomic evolution for breeding

Phylogeny not only indicates relationships but also helps understand the genomic structure of crops, which is critically important for breeding.

Brassica. The U triangle shows that allotetraploids contain complete genomes of two diploid species. This means that genes absent in one genome can be taken from the other. For example, B. napus (AACC) can obtain resistance genes from B. rapa (AA) or B. oleracea (CC). Synthetic amphiploids (for example, synthetic B. napus) are used to expand the genetic diversity of cultivated forms (Gupta, 2009, ch. 2).

Gossypium. Polyploidy in cotton led to gene duplication and neofunctionalization, which contributed to improved fiber quality. Understanding the genomic structure (A, D, AD) makes it possible to purposefully transfer genes from diploid species into tetraploids (Bayer and Kubitzki, 2003, ch. 6).

Amaranthaceae. Quinoa is a tetraploid, amaranth — diploids and polyploids. Polyploidy played a key role in adaptation to the high-mountain conditions of the Andes. Knowledge of genomic structure helps breeders use wild relatives to increase yield and resistance (Bhargava and Srivastava, 2013; Paredes-López, 1994).

5.4. Molecular markers and genomic technologies in phylogeny-based breeding

Modern breeding is unthinkable without molecular markers and genomic technologies. Phylogeny provides the basis for their application.

• Marker-assisted selection (MAS). Makes it possible to select plants with the desired genes at early stages, without waiting for phenotypic manifestation. Examples: MAS for resistance to clubroot in Brassica (QTLs on chromosomes 1, 2, 9), to nematodes in Beta (genes Hs1pro-1, R6m-1), to diseases in Gossypium (QTLs for resistance to Verticillium wilt).
• QTL mapping and GWAS. Make it possible to identify loci controlling complex traits (yield, quality, resistance). Examples: QTLs for fiber quality in cotton, QTLs for sugar content in beet, QTLs for protein content in quinoa.
• Genome editing (CRISPR/Cas9). Makes it possible to purposefully modify genes, including transferring alleles from wild species into cultivated ones. For example, editing glucosinolate genes in Brassica to improve taste and nutritional value (Gupta, 2009; Prohens and Nuez, 2008).

5.5. Conservation of genetic resources: priorities based on phylogeny

Phylogeny helps determine priorities for the conservation of genetic resources. Species phylogenetically close to cultivated ones should be conserved first, since they are potential donors of genes. For example:

• For Brassica, priority is given to wild populations of B. oleracea on the Atlantic coast, B. rapa in the Mediterranean, and B. nigra in Western Asia.
• For Beta — populations of B. maritima along the shores of the Mediterranean and Black Seas.
• For Gossypium — wild species in Australia, Africa, and America.
• For Chenopodium — wild populations of quinoa in the Andes, C. album in Eurasia.
• For Amaranthus — wild species in Mexico, Central America, and the Andes.

Conservation of these resources requires both ex situ (gene banks) and in situ (habitat protection) measures. Phylogenetic analysis helps identify “hotspots” of diversity and plan collection expeditions (Biancardi et al., 2012; Bhargava and Srivastava, 2013; FAO, 2011).

6.1. Three families — three pillars of world crop production

Brassicaceae, Malvaceae, and Amaranthaceae are not simply three taxa in a classification system. They are three pillars on which the food, industrial, and forage security of humanity rests.

Brassicaceae (mustards, crucifers) give us vegetables (cabbage, radish, turnip, broccoli, cauliflower), oilseed crops (rapeseed, mustard), forage (turnip, fodder cabbage), condiments (mustard, horseradish, cress), medicinal and ornamental plants. The model object Arabidopsis thaliana has made this family central to all modern plant biology (Gupta, 2009; Prohens and Nuez, 2008).

Malvaceae (mallow family) in the expanded circumscription includes cotton, the most important textile crop in the world, cacao — the basis of the chocolate industry, okra, durian, cola, linden — a source of wood and honey, hibiscus and hollyhock — popular ornamental plants. The unification of four former families (Malvaceae s.str., Bombacaceae, Sterculiaceae, Tiliaceae) into one monophyletic family became possible thanks to molecular systematics (Bayer and Kubitzki, 2003; Judd et al., 2018).

Amaranthaceae (amaranths) in the expanded circumscription (including Chenopodiaceae) include sugar beet, which provides about 20–25% of world sugar, spinach and garden beet, quinoa and amaranth — ancient grain pseudocereals with a unique amino acid composition, forage and medicinal plants, as well as noxious weeds that are simultaneously genetic resources (Kadereit et al., 2003; Bhargava and Srivastava, 2013; Draycott, 2006; Paredes-López, 1994).

Together, these three families cover virtually the entire spectrum of economic uses of plants: from food to clothing, from feed to medicines, from industrial raw materials to ornamental horticulture.

6.2. Diversity of life forms and ecological niches

One of the key observations we made during the lectures is the colossal diversity of life forms and ecological adaptations within each family.

Brassicaceae are predominantly herbs, but among them there are annuals, biennials, and perennials adapted to temperate, subtropical, and even Arctic conditions. Malvaceae are trees (baobab, ceiba, linden), shrubs, lianas, and herbs occupying tropical, subtropical, and temperate niches. Amaranthaceae are herbs, subshrubs, and shrubs, among which there are xerophytes (amaranth, saltwort), halophytes (beet, glasswort, saltbush), succulents, and even aquatic plants (Judd et al., 2018; Bayer and Kubitzki, 2003; Kadereit et al., 2003).

Such diversity means that representatives of these families can be cultivated almost everywhere — from the high Andes (quinoa) to arid deserts (amaranth, saltwort), from tropical plantations (cacao, cotton) to temperate fields (cabbage, beet, rapeseed). This makes them strategically important for adapting agriculture to climate change.

6.3. Phylogeny as a working tool for the agronomist

We have repeatedly emphasized that phylogeny is not an abstract scheme, but a practical tool. Molecular phylogenetic studies have made it possible to:

• Refine the circumscription of families. For example, the unification of Amaranthaceae and Chenopodiaceae (APG, 1998; Kadereit et al., 2003) and the expansion of Malvaceae through Bombacaceae, Sterculiaceae, and Tiliaceae (Bayer et al., 1999; Judd and Manchester, 1997).

• Understand the origin of crops. The “U triangle” (U, 1935) explains the origin of the allotetraploids Brassica napus, B. juncea, and B. carinata. Polyploidy in Gossypium (tetraploids AADD) and Chenopodium quinoa (tetraploid) has also been deciphered using cytogenetics and molecular markers (Gupta, 2009; Bayer and Kubitzki, 2003; Bhargava and Srivastava, 2013).

• Find donors of economically valuable traits. Wild sea beet Beta maritima is a source of resistance to nematodes (Biancardi et al., 2012). Wild species of Brassica and closely related genera are a source of resistance to clubroot (Prohens and Nuez, 2008). Wild species of Gossypium are a source of resistance to diseases and pests (Bayer and Kubitzki, 2003). Wild populations of quinoa and amaranth are a source of resistance to drought and salinity (Bhargava and Srivastava, 2013; Paredes-López, 1994).

• Apply molecular markers and genomic technologies. MAS, QTL mapping, GWAS, CRISPR/Cas9 — all these tools rely on phylogenetic knowledge about relationships and the genomic structure of crops.

6.4. Practical conclusions for the agronomist

What should an agronomist-practitioner take away from this course?

First. Knowledge of systematics makes it possible to correctly identify crops and their weed relatives. For example, to distinguish cultivated beet from wild Beta maritima, quinoa from white goosefoot, cultivated amaranth from redroot pigweed. This is important for phytosanitary control, seed production, and plant protection.

Second. Understanding phylogenetic relationships helps predict crossability and choose the correct breeding strategies. For example, to transfer resistance genes from B. carinata into B. oleracea, one must take into account their genomic constitutions (BBCC and CC, respectively), which determines the methods of hybridization and selection (Gupta, 2009).

Third. Knowledge of genetic resources and centers of origin makes it possible to purposefully search for donors of desired traits. For example, for drought resistance in quinoa, one should turn to populations from arid regions of Bolivia and Peru; for nematode resistance in beet — to populations of B. maritima from the Mediterranean (Bhargava and Srivastava, 2013; Biancardi et al., 2012).

Fourth. Understanding the biology and ecology of families helps develop agronomic technologies. For example, knowledge of C4 photosynthesis in amaranth explains its high productivity under high temperatures; knowledge of the halophytic nature of beet and quinoa allows them to be cultivated on saline soils (Paredes-López, 1994; FAO, 2011).

6.5. Prospects and challenges

Under conditions of global climate change, population growth, and reduction of arable land, the role of systematics and taxonomy in the agrosphere will only increase. Humanity faces challenges that cannot be solved without knowledge of biodiversity and phylogeny:

• Food security. Quinoa and amaranth are ancient crops that can become the basis of sustainable nutrition in regions where traditional cereals (wheat, rice, maize) suffer from drought, salinity, and diseases. Their systematics and genetic resources must be studied and conserved (FAO, 2011; Bhargava and Srivastava, 2013).

• Sustainable agriculture. Wild relatives of cultivated plants are a source of genes for resistance to diseases, pests, and abiotic stresses. Their conservation in situ and ex situ is a priority task (Biancardi et al., 2012; Prohens and Nuez, 2008).

• Bioeconomy. Oilseed Brassicaceae (rapeseed, mustard, camelina) are a source of biodiesel, lubricants, and bioplastics. Cotton is not only fiber but also a source of oil, cellulose, and biocomposites. Systematics helps identify new promising species (Gupta, 2009, ch. 17).

• Conservation of biodiversity. Many wild species of Brassicaceae, Malvaceae, and Amaranthaceae are threatened with extinction due to habitat destruction. Their conservation is not only an ethical but also a practical task, since they may contain genes necessary for future breeding.

6.6. Concluding word

We have examined three great families of plants that feed, clothe, heal, and adorn humanity. We have seen how molecular systematics and phylogeny have transformed our ideas about relationships and the circumscription of taxa, how knowledge of evolution and genomics helps breeders create new varieties, and how the conservation of genetic resources ensures food security.

Systematics and taxonomy are not simply “the science of names.” They are the foundation on which all agronomy is built. Without knowing what plant is in front of us, to which family and genus it belongs, what relatives it has and what traits they carry, it is impossible either to cultivate it effectively, or to improve it, or to protect it.

Remember: every variety of cabbage, every cotton plantation, every field of sugar beet, every cup of quinoa coffee is the result of millennia of evolution, human selection, and scientific knowledge. And systematics is the compass that helps us navigate this endless diversity of the plant world.