Various terms on plant classification are here reviewed grouping and describing plants according to their natural habitat or ecological adaptation. These terms facilitate communication and understanding about agricultural crops or potential crops for various purposes such as crop selection for gardening or crop farming, research and development, and plant collection. Substantial understanding of plant classification and plant adaptation is likewise important in applying more efficient methods for the commercialized production of crops.
In The Plants (1963), there is mention that the pygmy cedar (Peucepyllum) has the unique ability to live without soil water. It replenishes its water supply from the water vapor in the air at night time. This is amazing because it is always presumed that terrestrial plants naturally obtain water from the soil. After all, terrestrial plants have roots which are anchored on the soil.
With such information, it follows that it is possible to make productive any problem area by selecting crops which originated from similarly situated natural habitats. A list of crops under the different plant classifications, if available, will be a valuable reference.
Listed below in alphabetical order are various terms used in describing plants according to their natural habitat or environmental adaptation. Mostly examples of plants under each classification are provided.
1. Aquatic plants, hydrophytes, or hydrophytic plants, also called water-loving plants, are plants that are naturally adapted to growing in water or waterlogged soil. They may grow entirely or partly submerged, or floating on the water surface, or with their roots anchored to the ground in swamps or beside bodies of water.
They are able to thrive with watery places as their natural habitat due to special morphological and anatomical modifications mainly the presence of modified roots called "pneumatophores" which are responsible for oxygen absorption. Those pointed structures which protrude upward in some mangrove species (probably Sonneratia) during low tide are pneumatophores.
Some crops belonging to this plant classification are gabi or taro (Colocasia esculenta), lowland rice (Oryza sativa), members of water hyacinth family (e.g. Monochoria vaginalis), water lily (Nymphaea spp.), papyrus and umbrella plant (Cyperus spp.), lotus (Nelumbo nucifera), and bakawan (Rhizophora mucronata) and other mangrove species.
2. Acidifuge or calcicole plants, also called chalk-loving, lime-loving and acid-escaping plants, are plants that prefer calcareous or alkaline soils or soils with pH above 7.0. The alfalfa (Medicago sativa), blazing star (Chamaelirium luteum), and southern redcedar (Juniperus silisicola)are grouped under this plant classification (Stiling, 1999).
3. Calcifuge or acidicole plants, also called chalk-escaping, lime-hating, acidophilous, acid-loving, and acid soil plants, are those that prefer acidic soils or soils having pH levels below 7.0 but do not tolerate alkaline (basic) or calcareous soils. Crop examples under this plant classification are the rhododendrons and azaleas which have a low lime requirement and can live in soils with ph levels of 4.0 or less (Stiling, 1999).
4. Epiphytes or epiphytic plants, also called air plants and tree dwellers, are plants adapted to growing aboveground on another plant but they are not parasitic. They usually need the host only for physical support, deriving their nutritional requirements from the air and other sources.
Examples of common epiphytes are plants under the family Bromyliaceae including the ornamental bromyliads, and many plants belonging to the orchid and fern families.
A hemiepiphyte is a plant which starts growing as an epiphyte but, as it matures, becomes rooted to the soil. Example: strangler fig (Ficus).
5. Halophytes or halophytic plants, also called salt loving plants, are plants that can tolerate growing under saline conditions or in natural habitats which are excessively rich in salts. Included under the halophytic plant classification are the nipa (Nypa fruticans), talisay (Terminalia catappa), bakawan (Rhizophora mucronata) and many other mangrove species.
Coconut (Cocos nucifera), cashew (Anacardium occidentale), jackfruit (Artocarpus heterophyllus) and tamarind (Tamarindus indica) have varying tolerance to salinity. The common table salt is in fact used as a fertilizer for coconut.
6. Heliophytes or heliophytic plants, also called sun-loving plants, are those that require for their optimum growth full exposure to the sun. Examples are coconut, mango (Mangifera indica), sugarcane (Saccharum officinarum), corn (Zea mays). This plant classification applies more to the xerophytic plants.
7. Lithophytes or lithophytic plants are plants with special adaptation to growing on rocks or in rocky terrain having scant humus. They absorb nutrients from the air, rain, and decaying organic matter which accumulate on the rocks. Examples are orchids belonging to the genera Vanda, Ascocenda, Ascocentrum, and Trudelia.
8. Metallophytes are plants adapted to natural habitats with toxic levels of metals such as Ni, Co, Cr and Mn. Examples of metal-tolerant plants are Myristica laurifolia, Shorea tenuiramulosa, Rinorea bengalensis, Phyllanthus balgooyi, and Walsura monophylla (ISES, 2010).
9. Mesophytes or mesophytic plants, also called moist-loving plants, belong to the terrestrial plants. Their natural habitats consists of moderate conditions for plant growth. These conditions are described as not excessively dry but not too wet. Many cash crops which are grown in tropical climates having even distribution of rainfall are mesophytes. Most tropical crops including palms, banana and other fruit trees,and vegetables are mesophytes.
10. Neutrophilus plants or neutrophiles, are plants that can tolerate either acidic or alkaline soils.
11. Parasites or parasitic plants, are plants which grow on another plant (host) which they need as a source of nourishment, either partially or entirely. Examples are the mistletoe ( family Cassytha and Loranthaceae), Rafflesia, and orchids classified under the genera Neottia and Corallorhiza.
12. Phreatophytes are plants adapted to arid conditions by growing long roots which obtain water from underground reserves. The mere presence of these plants indicate a stable supply of underground water and such knowledge has been applied by digging wells close to them. Examples are the mesquite (Prosopis), cottonwood tree (Populus) and California fan palm (Washingtonia filifera).
13. Saprophytes or saprophytic crops refer to the mushrooms. They are not plants but fungi which have no green tissues. Their natural habitat consist of the dead or decaying organic matter from which they obtain their food.
Knowledge of their natural habitat has been put into use in their commercialized production. Mushrooms are grown on organic substrates such as banana leaves, rice straws and other plant leaves, saw dust and logs.
Examples of commercially grown mushrooms are the straw mushroom (Volvariella volvacea), button mushroom (Agaricus bisporus), Shiitake mushroom (Lentinus edodes), Flammulina velutipes, Pleorotus pulmonarius, and Auricularia polytricha.
14. Sciophytes or sciophytic plants, also called shade-loving plants, are those plants with special ecological adaptation to reduced light intensity or partial sun. Most of these plants are found naturally growing on the forest floor and under the canopies of trees with thick foliage. Examples are most orchids, ferns and fern allies like whisk fern (Psilotum nudum), horsetail (Equisetum spp.), clubmosses (Lycopodium spp.) and Silaginella spp.
Commercially grown crops associated with this plant classification include the black pepper (Piper nigrum), cacao (Theobroma cacao), coffee (Coffea spp.), lanzones (Lansium domesticum), mangosteen (Garcinia mangostana), soursop (Annona muricata), hot pepper (Capsicum annuum)and ginger (Zingiber officinale). These crops can tolerate or require shade and are therefore suitable for intercropping under coconut or other perennial crops having wide canopies.
15.Terrestrial plants, also called land plants, are those that grow on land with their roots in the soil. Their body parts are divided into two main groupings: the aerial parts and the underground parts. Most farm crops belong to this plant classification and are further grouped into special classifications such as heliophytes, mesophytes, sciophytes, etc.
16. Xerophytes, xerophytic or xeric plants, also called dry loving plants, are those having plant adaptation to regions with scant or no water and hot conditions. Their natural habitats are the arid and semi-arid regions and those places with long summer drought. A specialized type of landscaping which emphasizes the use of xerophytes is termed xeriscaping.
Examples of xerophytes are the members of the Lamiaceae and Compositae, the olive (Olea), and the succulents such as the cacti and those belonging to the genera Asparagus, Euphorbia, Agave, Aloe, Crassula and Sansevieria (botany.wisc.edu, 2009). The pineapple and other bromeliads are also included under this plant classification.
By knowing the natural plant adaptation of the various farm crops, the probability of crop failure can be minimized or prevented. A hydrophyte is suited under waterlogged area; a xerophyte for the drought-prone farm; a sciophyte for intercropping with perennial crops. Otherwise, provide what is lacking. For the plant breeders, the genotype can always be manipulated.
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(Ben G. Bareja 2010)