Ecological-Morphological Classification of I. G. Serebryakov

In botany, there are many definitions of life form (see, e.g., Warming 1908; Raunkiaer 1934). However, it is I. G. Serebryakov’s definition that is the most complete and biologically meaningful. He understood life form not merely as external appearance (habit), but as a peculiar general appearance of a particular group of plants, including their aboveground and underground organs, arising in ontogeny as a result of growth and development under specific environmental conditions and historically formed in given soil-climatic conditions as an expression of adaptation to those conditions (Serebryakov 1962).

Several important points follow from this definition:

Unlike the classification of the Danish botanist C. Raunkiaer, who used only one, albeit very important, trait – the position of renewal buds relative to the soil surface (Raunkiaer 1934) – I. G. Serebryakov proposed an integrated approach. Its essence is that the plant habit is determined by three groups of interrelated traits:

Based on these principles, I. G. Serebryakov identified four major divisions of life forms of seed plants (see diagram in Section 2):

Within each division, Serebryakov identified types, classes, subclasses, groups, and finally the life forms themselves, which are the basic taxonomic unit of the system (Serebryakov 1962). For example, in the division “Woody plants”, the type “Trees” is divided into classes: “Crown-forming trees with completely lignified elongated shoots”, “Rosette trees”, “Stem-succulent trees”, etc.

Thus, the ecological-morphological classification of I. G. Serebryakov is not just a field guide to appearance, but a deeply considered evolutionary system that allows one to read the history of a plant’s adaptation from its structure. This is precisely what makes it an indispensable tool for agronomists, foresters, or ecologists (more on practical significance in Section 4).

Serebryakov considered this criterion the leading one. It determines the assignment of a plant to one of the three main divisions of the classification (Serebryakov 1962).

As Serebryakov himself emphasized (1962), “the main content of the evolution of life forms in angiosperms from trees to herbs is associated with a reduction in the life cycle duration of aboveground skeletal axes.”

This complex criterion allows the differentiation of plants within each division. I. G. Serebryakov considered the following aspects (see also Barthélémy & Caraglio 2007; Serebryakova 1977):

For herbaceous perennials (polycarpics), the structure of the underground sphere is the key criterion determining membership in a particular subclass or group (Serebryakov 1962; Savinykh 2015).

I. G. Serebryakov and his followers identified the following main types:

As Savinykh (2015) notes, in modern biomorphology this scheme is supplemented by consideration of “phytocoenotic impact” (e.g., monocentric, polycentric plants) and the nature of morphological disintegration (ability to break down into partial shrubs). However, the foundations were laid precisely by I. G. Serebryakov.

Thus, the classification of life forms according to Serebryakov is a multi-stage system where the sequential application of criteria (axis longevity → growth pattern → underground organ structure) allows one to determine with high precision the place of any seed plant in the ecological-morphological space. The next section examines the main groups of this classification.

This group includes trees, shrubs, and dwarf shrubs. From an agronomic viewpoint, not only the perennial nature of aboveground skeletal axes is important, but also the nature of their growth and fruiting.

This division (semi-shrubs and dwarf semi-shrubs) includes species in which the lower part of the shoots lignifies and persists for several years, while the upper part is herbaceous and dies annually. Typical examples: lavender, wormwood, winterfat, some species of astragalus (Serebryakov 1962).

Agronomic significance: the need for periodic deep pruning for rejuvenation and to prevent the lower part of shoots from becoming bare; an important component of pasture ecosystems in arid zones (as forage plants).

This is the most extensive and agronomically diverse group. It is here that Serebryakov’s classification becomes an indispensable tool for a differentiated approach to cultivating forage grasses and controlling weeds.

Taproot perennials. The main root persists throughout life. Vegetative reproduction is absent or weak (alfalfa, goat’s-beard, dandelion, some clover species). Agronomic significance: they tolerate trampling and intensive grazing poorly, but their powerful taproot system facilitates deep soil loosening and the bringing up of nutrients from lower horizons (Williams 1922, cited in Serebryakov 1962). In agrophytocenoses, they are often edificators.

Fibrous-root and short-rhizome perennials. The main root dies early, and the plant is supported by a bunch (fibrous mass) of adventitious roots. Vegetative regeneration occurs via buds on a shortened caudex. Examples: timothy, orchard grass, meadow foxtail. Agronomic significance: these grasses form a loose tuft, regrow well after mowing, but do not spread. They are the basis of high-yielding hay meadows (Serebryakov 1962; Dmitriev 1948, cited in Serebryakov 1962).

Long-rhizome perennials. Characterized by the presence of long underground shoots – rhizomes – bearing renewal buds. Classic noxious weed – couch grass (Agropyron repens). Capable of quickly occupying large areas; during plowing, fragments of rhizomes give rise to new plants. Agronomic significance: knowledge of the life form allows choosing the correct control strategy – rhizome exhaustion (stubble peeling, deep plowing), combing out, application of herbicides acting on the underground sphere (Kott 1948, cited in Serebryakov 1962). At the same time, some long-rhizome grasses (smooth brome) are valuable forage plants on loose, well-aerated soils (Williams 1922, cited in Serebryakov 1962).

Stoloniferous and creeping perennials. Propagate via aboveground or underground stolons – thin, short-lived shoots that root at nodes. Examples: strawberry (aboveground runners), creeping buttercup (rooting creeping shoots), field mint. Agronomic significance: thanks to stolons, plants quickly occupy territory, which is useful as ground cover crops but harmful in crops due to eradication difficulty. Capable of vegetative juvenility: mother shoots die after fruiting, and daughter rosettes become independent plants (Vysotsky 1915, cited in Serebryakov 1962).

Tuber-forming and bulbous perennials. Form specialized storage organs – tubers (potato, Jerusalem artichoke) or bulbs (onion, garlic, tulip). Agronomic significance: this is a key group of vegetable crops. Understanding the morphogenesis of stolons and tubers (in potato) and bulbs (in onion and garlic) underlies storage, vernalization, and seed production technologies. Ephemeroid bulbous plants (tulips, squills) are used in landscaping.

These include species that complete their life cycle within one growing season. They lack perennial underground organs; they overwinter in the seed stage. This is the vast majority of grain crops (wheat, barley, oats, rice) and oilseeds (sunflower, mustard), as well as many weeds (pigweed, white goosefoot, gallant soldier).

Agronomic significance: their cultivation and control strategy is based on managing the soil seed bank. For spring crops, this involves crop rotation and sowing timing selection; for winter crops, the use of the vernalization stage (Lysenko 1949, cited in Serebryakov 1962). Control of annual weeds is reduced to provoking germination (early pre-sowing tillage) and their destruction by mechanical or herbicidal methods before seeding.

Thus, the “agronomic reading” of Serebryakov’s classification consists of a quick assessment of the root system type, regeneration and reproduction method, and the lifespan of aboveground and underground axes. This knowledge is the basis for decisions on tillage systems, crop rotation, pruning, mowing timing, and herbicide application.

The most widely known system worldwide (especially in phytocoenology and biogeography) is that of the Danish botanist Christen Raunkiaer (Raunkiaer 1934). It uses a single criterion: the position of renewal buds relative to the soil surface during the unfavorable season (winter or drought). Raunkiaer distinguished five main types: phanerophytes (buds high above ground), chamaephytes (buds low, up to 25-30 cm), hemicryptophytes (buds at soil level, protected by dead leaves), cryptophytes (buds under ground or water), and therophytes (annuals that survive the unfavorable season as seeds).

Strengths of Raunkiaer’s system: it is very simple, convenient for geobotanical descriptions, and allows comparisons of life form spectra of different climatic zones. For example, the “hemicryptophyte climate” is characteristic of the temperate zone, while the “therophyte climate” is typical of Mediterranean deserts (Raunkiaer 1934; see also Belousova et al. 2015). Due to this, Raunkiaer’s system has become an indispensable tool for global ecological comparisons.

Limitations of Raunkiaer’s system: it does not account for internal diversity within each group. For example, the hemicryptophyte group includes both short-rhizome grasses and rosette herbs and taproot perennials – with completely different agronomy and biology. The cryptophyte group includes long-rhizome, tuberous, and bulbous plants. Raunkiaer’s system is rather an “ecological” classification based on adaptation to climate (mainly to winter or drought conditions), whereas Serebryakov’s classification is “ecological-morphological,” considering the ontogenetic architecture of the plant (Serebryakov 1962; Savinykh 2015).

Conclusion: Raunkiaer’s system answers the question “how is the plant adapted to survive the unfavorable season?” Serebryakov’s system answers the question “how is the plant structured as a whole, what is its growth, regeneration, and space-occupying strategy?” They do not contradict but complement each other. Ideally, a botanist should use both classifications: the Raunkiaer spectrum for assessing the climatic condition of the flora, and the detailed Serebryakov classification for understanding population structure and vegetation dynamics (see, e.g., the use of both Raunkiaer and Serebryakov classifications in the work of Belousova et al. 2015 on weed plants of the Leningrad region).

In the 1970s, the British ecologist John Philip Grime proposed the concept of three primary plant strategies (CSR theory), based on resource allocation among three factors: competitiveness ©, stress-tolerance (S), and ruderalism ® – the ability to survive in disturbed conditions (Grime 1979).

This concept, which has gained wide international recognition, allows predicting plant behavior in ecosystems. However, for its practical application, one needs to know clearly the morphology and biology of the plant. Here, Serebryakov’s classification provides the missing links:

Relation between Serebryakov’s classification and Grime’s CSR strategy: the habit traits described in detail by Serebryakov (internode length, root system type, ability for vegetative spreading, etc.) are the direct morphological expression of the ecological strategy. If CSR theory tells “why” the plant behaves as it does (function), then Serebryakov’s classification tells “how” this is implemented in structure (form).

Thus, knowledge of the life form according to Serebryakov allows the agronomist and ecologist to quickly determine the plant’s strategy type according to Grime (see Section 5), without resorting to lengthy physiological experiments. For example, a long-rhizome grass (couch grass) is clearly a C-strategist with strong competitive abilities; a short-rhizome grass (timothy) is closer to a mesophytic strategy, while a dense-tussock grass (fescue) is an S-strategist, tolerant to stress.

In summary, Serebryakov’s classification, being “detailed-morphological” and “ontogenetic” in nature, fits organically into the global system of ecological concepts, providing concrete morphological content for more abstract functional models (Raunkiaer, Grime). It is this unique ability – to link external form with internal biology and species history – that has determined its long life and recognition in world science.

The composition of life forms in the grass stand or weed component of a crop serves as a reliable indicator of edaphic conditions. This is because each life form has specific ecological amplitudes with respect to moisture, aeration, density, and soil fertility.

Soil moisture and aeration. Long-rhizome perennials (couch grass, smooth brome, ground elder) are typical inhabitants of loose, well-aerated soils with adequate moisture (Williams 1922, cited in Serebryakov 1962). Their predominance in the weed component indicates relatively favorable water-air conditions. In contrast, dense-tussock grasses (sheep’s fescue, tufted hairgrass, moor grass) and many rosette herbs (greater plantain, dandelion) dominate on dense, poorly aerated soils, under conditions of overcompaction or excessive moisture (Williams 1922; Serebryakov 1962). The presence of rhizomatous sedges (Carex pilosa, Carex acutiformis) indicates temporary excess moisture and stagnant conditions.

Soil trophic status and acidity. Taproot perennials, especially legumes (alfalfa, red clover, sainfoin), are indicators of calcium-rich soils with a neutral reaction. Their presence in the grass stand indicates high potential fertility. Short-rhizome grasses (timothy, orchard grass) prefer moderately rich soils with good drainage. On acidic, poor podzolic soils, dense-tussock grasses (red fescue, common bent) and some fibrous-root perennials (sheep sorrel) dominate.

Example: In the study by E. N. Belousova and co-authors (2015) on weed plants of the Leningrad region, it was found that annual therophytes dominate (up to 38.5%) in fields (segetal habitats). On field edges and roadsides (ruderal habitats), the proportion of perennial hemicryptophytes increases sharply (up to 51.7%). Moreover, the floristic similarity between fields and surrounding biotopes is higher for perennial species, indicating that it is the perennial weeds not subject to plowing on field edges that are the main source of field infestation (Belousova et al. 2015). Thus, analyzing the life forms of the weed component allows not only assessing the agronomic background but also identifying reservoirs of harmful species.

The change in life forms over time is a classic indicator of restorative successions (stages of fallow or cutover overgrowth). Knowing the ecological-morphological features of plants, one can predict with high accuracy the course of the restoration process.

Knowing this sequence allows the agronomist and land user to make informed decisions: when it is advisable to bring fallow land back into crop rotation (at the stage dominated by annuals and rhizomatous grasses, when the soil is not yet overly structured), and when cultural measures (uprooting, rotary tilling) are needed to suppress perennial rhizomatous and root-sprouting weeds.

Serebryakov’s classification directly determines the choice of agronomic practices and plant protection products. Knowing the life form, one can predict the plant’s response to treatment.

Thus, agroecological assessment of a territory based on plant life forms is not an abstract academic exercise. It is a direct path to optimizing crop rotations, selecting tillage implements, developing integrated plant protection systems, and ultimately to increasing the productivity of agrocenoses and the sustainability of agricultural landscapes.