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This study describes the biomorphology of plants living under variable watering conditions. Its outcome expands the concept of a modular organization as a constructive and representative approach to comparative-morphological analysis and unraveling the ways of biomorph evolution. The structural organization of biomorphs growing in sites composed of gradients of humidification stability (from floodplain meadows to coasts, water cuts, and beaches) is examined on a base of systemic and complementary approaches. Model plant species—Solanum ulcamara, Thalictrum simplex, Lysimachia vulgaris, Lycopus europaeus, Stellaria palustris Persicaria amphibia, and Erysimum cheiranthoides—are studied. It is determined that acceleration in the vegetative and generative spheres entails the appearance of monocarps in the hygrophilic evolutional line. It is shown that the ontogenesis of individuals of seed and vegetative origin is reduced to a single fruiting, and the specificity of the shoot-formation model is preserved in plants of all the considered biotopes. Such a specific sign is identified as the internode elongation in the shoots located in the substrate, in the supersubstrate parts under flooding, in grass rags, or in dense grass under low light. Another sign is a sympodial growth by formation of the replacement shoots. On the model species, it is determined that plant adaptability is supported by the changes in individual structural elements of the monocarpic shoots; the structural and functional zonation of the monocarpic shoots determines the autonomization of the individual’s parts. Our results confirm the idea that the monocarpic shoot and the system formed on its basis belong to the category of axes of an herbaceous plant as part of an architectural unit (in terms of D. Barthelemy and Y. Caraglio). Our data make it possible to conclude that reservoir settlement with flowering plants is possible for long-shoot long-rhizome grasses and subshrub vines. Two evolutional directions are possible: (1) the emergence of monocarpic annuals and (2) the emergence of short-lived and annual plants of vegetative origin associated with the formation of acentric and clearly polycentric stolon-forming and root-shoot biomorphs.

Based on a biomorphological analysis, the structural organization of the Nelumbo nucifera Gaertn. plant is described. The shoot system is represented by semiroselatte polycarpic vegetative–generator axes; the shoot formation model is a monopodial semiroselatte. The anatomical structure of the N. nucifera stem, petiole, and peduncle corresponds to representatives of monocotyledon plants.

On the basis of biomorphological analysis of Solanum dulcamara, four ecobiomorphs of this plant are identified and described. They are a semi-woody vine, a subshrub with ascending shoots, a root sucker subshrub, and short-lived plants of vegetative origin. The structural units of individual plants, the sympodial shoot axes, are characterized by three variants of shoots: monocarpic renewals and sylleptic, vegetative sylleptic shoots with an incomplete cycle of development. The structural and functional organization of shoots and the development of sympodial axes in different ecobiomorphs, ensuring the ecological plasticity of S. dulcamara, are described.

The biomorphological diversity of riverside and aquatic herbaceous plants represented mainly by annual and biennial plants of vegetative origin, which replace perennial and biennial plants and annual, biennial, and winter monocarpics, has been studied. Depending on the season and moisture conditions, some species are represented by different basic biomorphs and phenobiomorphs. The modes of morphological evolution have been determined at the levels of individuals (abbreviations), shoots and their parts (abbreviations and the corresponding prolongations), and roots (prolongations). The role of the developmental features of monocarpic shoots in the habitat specificity of annual and biennial plants of vegetative origin has been described.

The modularity of flowering plants is considered using well-substantiated module categories: elementary, universal, and basic. Their structural diversity, which is regarded as a result of heterochrony at the level of organs, their elements, and whole organisms is shown. The heterochrony is considered to be a process of changes in the ontomorphogenesis of individuals, structural elements, and their parts in flowering plants; some of them are realized as heterotopies.

Nine species of helophytes are described using a systematic approach: Alisma plantago-aquatica, Butomus umbellatus, Sagittaria sagittifolia, Sparganium emersum, Glyceria maxima, Phragmites australis, Scirpus lacustris, Typha latifolia, and T. angustifolia. The species are divided into four groups according to their characteristics: monopodial rosette plants with a short rhizome, sympodial semirosellate plants with a short rhizome, sympodial semirosellate tuberous plants, and sympodial plants with a long rhizome. It is determined that seed individuals and vegetative descendants of polycarpic plants tend to become short-lived. This trend is implemented in different ways.

On the basis of the concepts of I.G. Serebryakov (founder of the science of plant life forms, ecological morphology) and an analysis of current data, the main directions of research and achievements of Russian botanists in studying life forms and the prospects for the development of biomorphology are shown. Plants are assessed as a distinctive group of living beings in the context of biological systems integrity. New approaches to habit characteristics, morphogenetic stages in relation to individual variations in ontogeny, and classifications of plant life forms are considered. The role of systemic and dynamic approaches in the description of plant life forms as modular organisms and the role of time as the fourth dimension and fundamental category in plant habit formation are discussed. Serebryakov’s assumption about the evolutionary system of biomorphs as a system of parallel series of life forms similar to homologous series of genetic variation is confirmed.

The life form of G. conopsea (short-lived perennial with annual vegetative renewal) makes it possible to combine the long-term, complete ontogeny and polycarpy of the genet with the short life span and monocarpy of individual daughter ramets. Annual changes in the structural organization of daughter individuals allow the plants to adapt to changing environmental conditions and retain the territory they have occupied. Organismal mechanisms providing for the sustainable development of G. conopsea plants in marginal populations are considered in the context of the concept of multivariant plant ontogeny.