Deciduous means "temporary" or "tending to fall off" (deriving from the Latin word decidere, to fall off).
When referring to teeth it means the teeth at the front of the mouth that grow and fall out and are replaced in childhood. They are called deciduous teeth.
In botany and horticulture, deciduous plants are trees, shrubs and herbaceous perennials which lose all of their leaves for part of the year. This is called abscission. Leaf loss happens in winter in temperate or polar climates.
With evergreens, foliage is shed differently from deciduous trees. They seem green year round. Plants that are intermediate may be called semi-deciduous; they lose old foliage as new growth begins. Other plants are semi-evergreen and lose their leaves before the next growing season, keeping some in winter or dry periods. Some trees, including a few species of oak, have desiccated leaves that stay on the tree through winter. These persistent dry leaves are dropped in the spring as new growth begins.
Many deciduous plants flower during the period when they are leafless, as this increases the effectiveness of pollination,Also the absence of leaves improves wind transmission of pollen for wind-pollinated plants and increases the visibility of the flowers to insects in insect-pollinated plants.
Plants with deciduous foliage have advantages and disadvantages compared to plants with evergreen foliage. Since deciduous plants lose their leaves to conserve water or to better survive winter weather conditions, they must regrow new foliage during the next suitable growing season; this uses resources which evergreens do not need to expend. Evergreens suffer greater water loss during the winter and they also can experience greater predation pressure, especially when small. Losing leaves in winter may reduce damage from insects; repairing leaves and keeping them functional may be more costly than just losing and regrowing them. Removing leaves also reduces cavitation which can damage xylem vessels in plants. This then allows deciduous plants to have xylem vessels with larger diameters and therefore a greater rate of transpiration (and hence CO2 uptake as this occurs when stomata are open) during the summer growth period.
Deciduous woody plants
The deciduous characteristic has developed repeatedly among woody plants. Trees include maple, many oaks and nothofagus, elm, aspen,and birch, among others, as well as a number of coniferous genera, such as larch and Metasequoia. Deciduous shrubs include honeysuckle, viburnum, and many others. Most temperate woody vines are also deciduous, including grapes, poison ivy, Virginia creeper, wisteria, etc. The characteristic is useful in plant identification; for instance in parts of Southern California and the American Southeast, deciduous and evergreen oak species may grow side by side.
Periods of leaf fall often coincide with seasons: winter in the case of cool-climate plants or the dry-season in the case of tropical plants, however there are no deciduous species among tree-like monocotyledonous plants, e.g. palms, yuccas, and dracaenas.
Forests where a majority of the trees lose their foliage at the end of the typical growing season are called deciduous forests. These forests are found in many areas worldwide and have distinctive ecosystems, understory growth, and soil dynamics.
Two distinctive types of deciduous forest are found growing around the world.
Temperate deciduous forest biomes are plant communities distributed in North and South America, Asia, Southern slopes of the Himalayas, Europe and for cultivation purposes in Oceania. They have formed under climatic conditions which have great seasonable temperature variability with growth occurring during warm summers and leaf drop in autumn and dormancy during cold winters. These seasonally distinctive communities have diverse life forms that are impacted greatly by the seasonality of their climate, mainly temperature and precipitation rates. These varying and regionally different ecological conditions produce distinctive forest plant communities in different regions.
Tropical and subtropical deciduous forest biomes have developed in response not to seasonal temperature variations but to seasonal rainfall patterns. During prolonged dry periods the foliage is dropped to conserve water and prevent death from drought. Leaf drop is not seasonally dependent as it is in temperate climates, and can occur any time of year and varies by region of the world. Even within a small local area there can be variations in the timing and duration of leaf drop; different sides of the same mountain and areas that have high water tables or areas along streams and rivers can produce a patchwork of leafy and leafless trees.
Deciduous Facts for Kids. Kiddle Encyclopedia.