Growth Habits in Plants
Growth habits in plants refer to the distinctive forms and structures that plants evolve based on genetic and environmental factors. The development of a plant body occurs through growth, which involves the increase in cell number and size, typically achieved through two methods: geometric increase, where many cells divide simultaneously, and arithmetic increase, where division occurs in a localized manner. These growth habits are influenced by conditions such as light, water availability, and soil quality, which drive adaptations aimed at survival and reproduction.
Plants exhibit a variety of growth habits, including climbing, clump-forming, dense, erect, mat-forming, mound-forming, open, prostrate, scandent, spreading, and stemless forms. Each of these forms has evolved to optimize a plant's ability to thrive in specific environments and to withstand challenges like grazing, wind, and limited resources. For example, climbing plants, or vines, utilize support structures to reach sunlight, while dense plants grow close together to maximize space and resilience in their habitats. Understanding these diverse growth habits provides insight into how plants interact with their ecosystems and adapt to changing environmental conditions.
Growth Habits in Plants
Categories: Angiosperms; gardening; physiology
Growth of Plants
Development of a plant body is accomplished through growth, defined as increase in number of cells and size of a species. Rates of growth in plants are achieved in two ways: first, by geometric increase, in which all cells of the organism divide simultaneously, especially in a young embryonic plant; second, by arithmetic increase, in which only one cell undergoes division, especially in mature plants with localized growth in a region at the root and shoot apices. Generally, plants grow by a combination of both kinds of cell division to produce variations of form that finally develop a specific habit that is unique to a particular plant species.
Evolution of Growth Habits
The primary purpose for the evolution of different growth habits in plants is adaptation for permanent survival and reproduction of new individuals, typically under changing climatic conditions. Water availability, especially during the growing season, is the single most important environmental factor that limits plant distribution and productivity on a global basis. Competition in the past among plants for available water, nutrients, space, and light enhanced the evolution of adaptive growth forms in plants.
Some plants developed wood as a mechanism to counteract the destructive effects of wind, ice, mechanical damage, and fire. Erect and dense growth habits evolved to resist wind effects and other mechanical damages. Plants without wood adapted prostrate, mat-forming, spreading, creeping, or climbing habits.
As animals interacted with plants and in the past, both evolved simultaneously. Various plants developed prostrate and mat-forming habits in order to endure intense grazing and trampling, or erect and tall growth forms to escape browsing and grazing.
In the past, individual plants that were able to adapt, survive, and produce more offspring were selected naturally for success. Different plants with varied growth habits colonized different habitats, becoming the dominant plants (largest or most abundant), and thereby the principal contributors in characterizing and sustaining different biomes. The various kinds of growth habits which evolved result in a variety of forms. It is not uncommon for one species of plant to exhibit growth habits among its different varieties.
Climbing Plants
Climbing plants are also called vines. The stems trail along or coil around other plants or structures as they grow upward. Examples include cucumber (Cucumis sativus), morning glory (Ipomea species), and grape vine (Vitis species). Climbers characterize moist forests and woodlands.
Clump-Forming Plants
Clump-forming or tussockyplants exhibit an aggregate of several shoots growing in a bunch from a common base, especially in grasses. Examples include the bunch grasses Andropogon and Aristidamosses (such as Polytrichum species) and sedges (Carex stricta). They characterize grasslands and are common in the prairies of the United States. They also grow in sandy locations, wetlands, and disturbed habitats.
Dense Plants
Dense plants grow many small, woody canes or stems very close together in an upright fashion. The majority are shrubs. Examples include Ephedra, southern arrowwood (Viburnum dentatum), mountain laurel (Kalmia latifolia), and creosote bush (Larrea tridentata). They characterize woodlands, grasslands, coastal vegetation, and deserts.
Erect Plants
In erect plants, one main stem grows in an upright position clearly above ground level. This is common in trees. Examples include banana (Musa), oak (Quercus), pine (Pinus), maple (Acer), and palm. They mainly characterize forests and woodlands and some grasslands.
Mat-Forming Plants
Mat-forming plants have many stolons (creeping stems) that grow in a trail along soil or water surfaces and spread out to produce a matlike cover. Examples include the grasses Cynodon and Digitaria, Kentucky bluegrass (Poa pratensis), crab grass (Digitaria sanguinalis), the aquatic fernsSalvinia and Azolla, and mosses, such as Sphagnum. They characterize grasslands, bogs, wetlands, secondary forest floors, and cultivated habitats.
Mound-Forming Plants
Mound-forming plants grow to form a rounded shape resembling a mound or swollen bump. Examples include the barrel cactus (Ferocactus and Echinocactus), several other species of cacti (such as Gymnocalycium), and Euphorbia gymnocalycioides. They characterize deserts, grasslands, and the tundra.
Open Plants
Upright, woody stems or canes growing in an erect fashion characterize open plants. Their growth resembles a dense habit but has fewer stems and an open, airier structure. Examples include some bamboos (Bambusa), black willow (Salix nigra), smooth alder (Alnus serrulata), and meadowsweet (Spirea). This is characteristic of some shrubs and small trees of forests, woodlands, wetlands, and grasslands.
Prostrate Plants
The stems of prostrate plants grow flat on the soil surface or almost touching (hugging) the ground but not trailing. Examples include the herbaceous milk-purslane weed (Euphorbia supina), common mullein (Verbascum thapsus), and some species of juniper. They are common in the tundra, grasslands, wetlands, and disturbed habitats.
Scandent Plants
Scandent plants have prominent stems in a leaning position. Examples include sugarcane (Saccharum officinarum), coconut palm (Cocos nucifera), bearberry (Arctostaphylos uva-ursi), blackberry (Rubus fruticosus), and some bamboos (Bambusa). They characterize the dwarfed, woody trees in the timberline of the tundra, savanna, forest undergrowth, and coastal habitats.
Spreading Plants
Spreading plants exhibit a sprawling type of growth, resulting from profuse lateral branching in mostly woody or succulent stems. Examples include common juniper (Juniperuscommunis), blueberries (Vaccinium), prickly-pear cactus (Opuntia), Sumacs (Rhus), and ferns (such as Adiantum). They characterize forest undergrowth, grasslands, sandy coastal areas, deserts, cultivated lands, and some areas of the tundra.
Stemless Plants
Stemless plants have no visible stem aboveground and are composed mainly of leaves or leaflike structures. Examples include common dandelion (Taraxacum officinale), Aloe vera, sisal (Agave), onion (Allium cepa), and liverworts (such as Marchantia polymorpha). They characterize aquatic and wetland vegetation, deserts, some grasslands, cultivated land, and wasteland.
Bibliography
Bold, H. C., et al. Morphology of Plants and Fungi . New York: Harper and Row, 1987. Provides extensive detail on growth forms in all families of plants. Includes illustrations, bibliographical references, and index.
Mauseth, James D. Botany: An Introduction to Plant Biology . Sudbury, Mass.: Jones and Bartlett, 1998. Discusses the broad variety of plant life-forms that colonize different biomes of the world. Includes good pictures, illustrations, and index.
Pearson, Lorenz C. The Diversity and Evolution of Plants . Boca Raton, Fla.: CRC Press, 1995. The author discusses the origins of the wide variety of plants and the different life-forms that exist.
Rost, Thomas L., et al. Plant Biology. New York: Wadsworth, 1998. Outlines the essentials of plant growth and organization and relates the facts to good descriptions of biomes and plant habits.