Inflorescence

Main axis (axis of inflorescence, floral axis). This is the central stem from which lateral branches arise. The stem bearing the entire inflorescence is called the peduncle (Yakovlev et al., 2008; Bell, 1991). If the inflorescence consists of a single flower, its stem is usually called the pedicel (see below).

Lateral axes. These are branches of various orders arising from the main axis. On them, in turn, may be axes of the next order or the flowers themselves. The totality of all axes of the inflorescence forms its architecture.

They are often smaller, may have a simple shape, be membranous, scaly, or reduced to inconspicuous outgrowths.

In some plants, bracts are, on the contrary, large and brightly colored, serving as attractants for pollinators (e.g., white bracts in dogwood, red bracts in poinsettia).

In some cases, bracts may be completely absent. Such inflorescences are called ebracteate (naked) (Serebryakova et al., 2006).

Raceme. Main axis elongated, flowers on well-developed pedicels of approximately equal length. Examples: bird cherry, lupine, cabbage (in seed).

Corymb. A variant of a raceme with a shortened main axis and unequal pedicel length: lower pedicels longer than upper ones, so that all flowers are at approximately the same level. Example: pear, spirea (Yakovlev et al., 2008).

Spike. Main axis elongated, but flowers sessile (without pedicels). Example: plantain, orchis. In grasses, the compound spike (see below) is the most important inflorescence of cereal crops (Sakuma et al., 2020).

Spadix. A spike with a greatly thickened, fleshy main axis. Often surrounded by a large bract – a spathe. Characteristic of aroids (calla lily), as well as maize, where the female inflorescences are cobs (Bell, 1991).

Catkin. A pendulous spike (rarely a raceme), usually bearing unisexual flowers and falling as a whole after fruiting. Typical of wind-pollinated trees (birch, willow, poplar) (Yakovlev et al., 2008).

Head. Main axis greatly shortened and expanded, flowers sessile or on very short pedicels, gathered in a dense cluster. Example: clover, alfalfa.

Capitulum. A specialized head with a flattened, dish-shaped receptacle on which sessile flowers are densely arranged. The capitulum is surrounded externally by an involucre of modified bracts. This is the characteristic inflorescence of the family Asteraceae (Compositae) – sunflower, aster, dandelion (Ahn, 2025; Yakovlev et al., 2008).

Umbel. Pedicels of approximately equal length arise from the apex of a shortened main axis. A simple umbel is characteristic of cherry, primrose.

Panicle. A compound, repeatedly branched inflorescence in which the degree of branching of lateral axes decreases from base to apex (pyramidal form). Partial inflorescences are simple racemes or spikes. Examples: lilac, grape, oat, rice (Dreccer et al., 2019; Park et al., 2012). In grasses, oats, millet, and rice have a panicle.

Compound spike. The main axis bears sessile partial inflorescences – spikelets, each of which is a simple spike (in grasses, of several flowers covered by scales). This is the typical inflorescence of wheat, rye, barley (Sakuma et al., 2020).

Compound umbel. Partial inflorescences (simple umbels called umbellets) arise from the apex of the main axis on rays of unequal length. Characteristic of the Apiaceae family (Umbelliferae) – dill, carrot, coriander.

Compound corymb. Partial inflorescences (short racemes or corymbs) are arranged on the main axis such that they all lie in approximately the same plane. Example: rowan, viburnum.

Dichasium. Under the terminal flower, two opposite lateral axes develop, which also end in flowers and can branch similarly. The result is a forked inflorescence. Example: chickweed, carnation.

Monochasium. After flowering of the main axis, only one lateral axis develops, which also ends in a flower. Depending on the arrangement of subsequent flowers, helicoid cyme (flowers arranged spirally) and scorpioid cyme (flowers arranged zigzag in one plane) are distinguished. Examples: forget-me-not, gladiolus (Bell, 1991; Hayashi and Konishi, 1991).

Xylem (from Greek xylon – wood) provides the upward flow of water and minerals from the roots to the flowers and leaves of the inflorescence.

Phloem (from Greek phloos – bark, bast) provides the downward flow of organic substances, mainly sucrose, from photosynthetic leaves to growing flowers and ovules (Serebryakova et al., 2006).

Collenchyma is located directly under the epidermis and consists of living cells with unevenly thickened walls. It provides strength to young, growing inflorescence axes.

Sclerenchyma consists of dead cells with evenly thickened, often lignified walls (sclereids or fibers). It forms a continuous cylinder or strands in the cortex and pith, providing exceptional resistance to bending and compression (Yakovlev et al., 2008).

Trichomes can perform a protective function (against insect herbivory, overheating) and participate in creating a microclimate around young buds.

Glandular hairs and nectaries are often located on the inflorescence axes and bracts. They secrete nectar, which attracts insect pollinators. In some plants (e.g., cotton), there are extrafloral nectaries on the bracts and pedicels (Yakovlev et al., 2008; Spitzer-Rimon et al., 2019).

Photoperiodic sensitivity. In many species (especially plants of temperate latitudes), inflorescence initiation is induced by a specific day length. For example, in the short-day plant Cannabis sativa, under long-day conditions (16 h) solitary flowers form in leaf axils, but upon transition to short days (12 h) intense branching occurs, forming compound racemose inflorescences (Spitzer-Rimon et al., 2019). Thus, photoperiod influences not only flower initiation but also inflorescence branching architecture.

Light intensity and quality. Low light or shading generally leads to elongation of internodes in the inflorescence (etiolation), which can reduce its compactness. High far-red (FR) light content, characteristic of shaded conditions, in many species stimulates inflorescence branching and can cause “vegetative reversion” — transformation of flowers into vegetative shoots (Dreccer et al., 2019; González-Suárez et al., 2025).

Effect on phenology. Elevated temperature accelerates inflorescence development and maturation, shortening the time from budding to flowering. This can lead to a reduction in flower number due to faster progression through initiation phases (Dreccer et al., 2019). Low temperatures, conversely, slow growth and may promote an increase in flower number per inflorescence, as the meristem remains in the vegetative phase longer (González-Suárez et al., 2025).

Temperature stresses. High temperatures (heat) during generative organ formation often lead to pollen sterility, manifesting as reduction of apical flowers (abortion) and reduced seed set per fruit (Chabert and Mallinger, 2025; Sakuma et al., 2020). In cereals, heat stress during meiosis causes spikelet sterility. Low freezing temperatures (frosts) during flowering can damage flowers, leading to empty grains and crop failure.

Vernalization. In winter and biennial crops, a prolonged exposure to low temperatures (vernalization) is required for the transition to inflorescence formation. Without such treatment, the plant remains in a vegetative state (González-Suárez et al., 2025).

Nitrogen. High soil nitrogen content stimulates vegetative growth but can also increase inflorescence size (raceme length, flower number) in many crops, if not exceeding a certain threshold (Landrein et al., 2025). However, excess nitrogen often leads to excessive internode elongation, stem lodging, and reduced inflorescence strength. Nitrogen deficiency, on the contrary, reduces flower number and causes premature cessation of inflorescence development.

Phosphorus. Phosphorus deficiency is critical at the stage of flower initiation. Phosphorus starvation slows inflorescence formation, reduces flower number, and lowers fertility (number of set seeds) (Chabert and Mallinger, 2025).

Effect on branching. In tomato and other solanaceous plants, improved mineral nutrition can enhance inflorescence branching by extending the period of meristem activity (Park et al., 2012). Conversely, nutrient deficiency often leads to reduction of lateral inflorescence branches.

Flower reduction. Drought during budding and flowering causes massive flower abortion, especially in the upper (apical) part of the inflorescence, where the youngest, most competitive flowers are located (Hayashi and Konishi, 1991). This phenomenon is well studied in cereals (wheat, maize) and legumes (soybean).

Ovary abortion. With prolonged water deficit, the processes of pollination and fertilization can be disrupted, and developing ovaries may die. This manifests as the formation of “empty” fruits without seeds (Chabert and Mallinger, 2025).

Structural changes. In some species, under moisture deficiency, inflorescences become more compact, with shortened internodes, which is an adaptive response to reduce transpiration (Doidy et al., 2024).

Pruning (removal of lateral shoots). In tomato, pepper, eggplant, and other solanaceous crops, removal of excess vegetative shoots (suckers) redirects assimilates to the remaining inflorescences. A more drastic operation — removal of part of the inflorescences (crop load regulation) — allows obtaining larger and more uniform fruits (e.g., in large-fruited tomato, pepper varieties) (Park et al., 2012).

Topping (removal of inflorescence apex). In maize, removal of the male inflorescence (tassel) at the tasseling stage (topping) stimulates assimilate flow to the developing ears and is used to produce seed maize and prevent unwanted cross-pollination. In ornamental crops, topping the main shoot induces inflorescence branching (e.g., in chrysanthemum).

Use of growth regulators. Retardants (e.g., chlormequat chloride, paclobutrazol) inhibit cell elongation, leading to shortening of inflorescence internodes, increased stem strength (lodging resistance), and sometimes increased flower number (Landrein et al., 2025). Flowering stimulants (gibberellins) can induce inflorescence development in some crops under unfavorable conditions, but their use must be cautious, as they can cause vegetativization (prolification) (González-Suárez et al., 2025).

Assessment of yield components. In cereal crops, direct counting of the number of productive spikes per unit area, number of spikelets per spike, and number of grains per spikelet underlies yield structure calculations (Sakuma et al., 2020). In sunflower, the number of achenes per capitulum correlates with the capitulum diameter, which is easy to measure. In tomato and legumes, the number of flowers per inflorescence (raceme) is a predictive trait of potential yield (Park et al., 2012).

Breeding for desired architecture. Genes controlling inflorescence branching are targets for breeding. For example, in tomato, alleles of the COMPOUND INFLORESCENCE (S) gene, which cause formation of compound branched inflorescences, have been fixed in some varieties to increase yield (Park et al., 2012). In cereals, genes responsible for spikelet number (FRIZZY PANICLE, etc.) are used to create forms with more productive compound spikes or panicles (Sakuma et al., 2020; Ahn, 2025).

Use of heterosis. For many cross-pollinated crops (rye, sunflower, maize), the production of hybrid seeds requires an effective system for controlling pollination. Understanding the structure of male and female inflorescences, as well as the phenology of their flowering, is critically important for organizing hybridization (Chabert and Mallinger, 2025).

Selection of pollinator varieties. When establishing an orchard or sowing a field, it is important to place inter-fertile varieties in close proximity to each other. The flowering periods of the varieties must coincide, and their inflorescences must be compatible with respect to genetic self-incompatibility (SI) or early inbreeding depression (EID) factors (Chabert and Mallinger, 2025). For example, for the apple variety ‘Antonovka’, suitable pollinators with simultaneous flowering are ‘Anis’, ‘Shtreifling’.

Use of pollinators. In protected cultivation (greenhouses), bumblebees (Bombus terrestris) or honeybees are used for pollination of tomatoes, peppers, and eggplants. Pollination efficiency directly depends on inflorescence architecture: in tomato, the raceme should be open and accessible to insects (Dreccer et al., 2019).

Phenological forecasts. Knowledge of inflorescence development phases (budding, flowering) allows timely application of fertilizers, irrigation, pest control treatments, and accurate determination of harvest dates. For stone fruit crops (cherry, apricot), it is important to forecast flowering dates to choose optimal timing for protective measures against frost.

Fungal diseases. Loose smut of cereals (Ustilago tritici, U. nuda) infects the inflorescence at the heading stage, turning the spike into a mass of dark spores. Septoria and Fusarium head blight cause death of flowers and grains. Fungicide treatments must be carried out strictly at the stem elongation and early heading stages (Sakuma et al., 2020).

Bacterial and viral diseases. Fire blight of fruit crops penetrates through flowers, causing wilting and blackening of inflorescences. Tobacco mosaic virus (TMV) infects tomatoes through pedicels.

Pests. Apple blossom weevil (Anthonomus pomorum) lays eggs in buds, causing them to dry out. Thrips and aphids often concentrate in inflorescences. Agronomic monitoring of the budding phase is necessary for timely application of insecticides.

Use of resistance. Breeding varieties with dense, closed inflorescences (e.g., cabbage – head) that are less accessible to pests and pathogens is an important direction.

Adaptation to drought. In drought-tolerant wheat and barley varieties, the inflorescence (spike) often has a waxy bloom, small scales, and the ability to abort the least valuable (apical) flowers under water deficit (Hayashi and Konishi, 1991; Sakuma et al., 2020).

Lodging resistance. Short, compact inflorescences with thick peduncles and well-developed mechanical tissue (sclerenchyma) are less prone to lodging. This trait is selected for in cereals and ornamental crops (Ahn, 2025).

Use of stress protectants. Treatment of plants with salicylic acid, brassinosteroids, or abscisic acid at the budding stage can increase inflorescence thermo- and drought tolerance, reducing flower abortion (Chabert and Mallinger, 2025; Landrein et al., 2025).