The importance of classification
All objects are named and classified for practical purposes. Human beings, animals, birds, and insects have special names and classes. Even non-living entities have their names and classes. A special set of terms and names is
associated with every business, trade, andprofession. Crop plants are no exception. Classification helps in the identification of related crop plants used for various purposes such as food, feed, and fiber. Moreover, classifi-
cation is essential for orderly reference and avoiding confusion in identification. For example, there are more than 300 kinds of clover, which are similar in appearance but differ from one another in specific ways. It is
difficult to ideritify and refer to them unambiguously without proper naming and classification.
Although many plants have common names, some species are so limited in extent or little known that they have not been commonly named. The common names in different countries are different according to the local language. Even within the same country and the same language, the common names are different in different parts of the country. The situation becomes more difficult when the same common name is given to a totally different species in different countries or parts of the country. Long ago it
This is the most important and oldest classification of plants. This idea has been developed and updated many times since its introduction in 370 B.C. by Theophrastus. Carl Van Linne (1707-1778), commonly known as Carolus’
Linnaeus, introduced another system of recognizing plants. His nomenclature remains the conventional system; The plant kingdom may be divided on the basis of structural characteristics into the following four divisions or
1. Thallophyta. These are the lower forms of plants. They do not have roots, stems, or leaves. They Include the algae, bacteria, and fungi. The most familiar plants of this group are mushrooms and bread molds. The nitrogen-
fixing bacteria in symbiosis with leguminous plants which increase soilfertility and productivity are thallophytes. Many of the principal causes of serious plant diseases like smuts and rusts arc fungi.
2. Bryophyta. The bryophytes are small green plants higher in the scaleof plant life than the thallophytes. They include the mosses, liverworts, and
hornworts. They grow in wet places and are widely distributed worldwide. None of them are cultivated for human use, and they so far have no economic importance.
3. Pteridophyta. These are green plants with vascular tissues, roots, leaves, and stems. They do not have flowers and seeds, hut reproduce themselves by spores. Psilophytes, club mosses, horsetails, and ferns belong to this
group. They do not have any agronomic value except as ornamentals.
4. Spermatophyta. This group includes the most highly developed forms of plant life. The spermatophyta produce seeds and bear true flowers. This division is further divided into two subdivisions.
Monocotyledons are those plants which have a single cotyledon in the seed. Germination is usually hypogeal, the cotyledons remaining below the ground. The most important plants in this group, such as maize, wheat, sorghum, and barley, belong to the grass family Gramineae.
Dicotyledons are those plants which have two cotyledons in the seed. Germination is usually epigeal, that is, the cotyledons come out above the ground during germination. The plants are usually broad- leaved. Typical dicotyledonous plants are gram, soybean, cucurbits, cotton, and tobacco.The basic unit in plant classification is the species. It is the working unit for agronomists, breeders, and botanists. A species can be defined as a
group of plants that normally breed among themselves and have many characters in common. Usually species do not cross with dissimilar groups of plants under natural conditions. Closely related species are grouped together into a genu-s, (plural genera and adjective generic). Closely related genera are then grouped into a family. Closely related families are grouped into orders; orders in turn are grouped into classes; and then classes into divisions or phyla. Taking common wheat as an example, it will be categorized in the following manner.
Variety and cultivar, At present three terms, botanical variety, variety, and cultivar are used. When a group of plants occurring in nature is different from the general species originally described, and the botanical binomial name is not enough to identify it, it is classified as a botanical variety below that of species. In general; the term variety has been used to refer to a group of similar plants within a particular species that is distinguished by one or more than one character and given’ a name. A cultivated variety is different from a botanical variety and is called a eultivar. ‘Cultivar’ is the contraction of ‘cultivated variety’, in which ‘var’ tands for varietas, Latin for ‘variety’. In order to avoid confusion with the botanical variety, the term cultivar has been suggested as the preferred term’. There are two main categories of cultivars: clones and lines. A cultivar propagated by vegetative methods is called a clone, and one propagated by ed is called a line. In common usage, the line is further divided into three categories: line, open-pollinated, and hybrid. A line is the product of a pure-breeding or self-pollinating plant. An open-pollinated cultivar is the product of open or cross-pollination. A hybrid cultivar results from controlled cross-pollination repeated each time new seed is produced. A cultivar is distinctly different from any plant already in cultivation. It may have a different flower color, number of spines, or presence or absence of pubes-
cence. The word cultivar is abbreviated ‘cv.’, and the plural is ‘cvs.’. The cultivar name is always capitalized but never underlined or italicized. It may be identified as a cuItivar by single quotation marks, e.g. ‘Golden Delicious’
Nomenclature or naming of plants. Most plants are usually known by their common local names, which are different from country to country and locality to locality. For example, in the USA ‘pumpkin’ refers to the species
Cucurbita pepo, a large, round, orange-yellow fruit, while in Britain ‘pumpkin’ can refer to any of several species of squash, e.g. Cucurbita moschata or C. maxima. In order to avoid confusion and to facilitate international com-
munication, in scientific writing a plant is given one name-its scientific, technical, or botanical mime. According to the internationally accepted rule, each plant has a two-word or binomial name given in Latin. The first name
refers to the genus and the second to the species. The initial of the person (authority) who names a plant species or variety is listed after the species name. For example, in the name Triticum aestivum L., ‘L’ means Linnaeus,
who named the wheat plant. The generic name always begins with a capital letter and the species name with a lower-case letter. These names are underlined if written by hand or typewriter and italicized when printed. The name
or abbreviated name of the authority appears in Roman (not italic) type.
Agronomic use classification
The major agronomic crop plants are grouped according to the way they are used. For example:
Cereal crops. A cereal is defined as a grass grown for its edible seed. Cereals are also known as grain crops. The major cereal crops are wheat, maize, rice, barley, oat, rye, triticale, sorghum, and millet.
Forage crops. Those crops which are grazed by animals or harvested for green chop, hay, silage, or soiling are classified as forage crops. More technically, forages have been defined as plant material with a dry-matter fiber content over 25%. When maize, sorghum, or other coarse grasses are harvested as whole plants and cured for animal feed, they are termed fodder. Most of the forage crops belong either to the grass family Gramineae or the Leguminoseae, e.g. grasses and clovers, respectively.
Fiber crops. These are crops which are grown for their fiber and are used in making textiles, ropes, and rugs. Important fiber crops are cotton, jute, flax, sunkukra, sunhemp, kenaf, and sial.
Sugar crops. Sugar crops include sugarcane, sugar beet, and sweet sorghum.
Oilseed crops. These are crops which are grown for the purpose of extracting oil from their seed. The main oilseed crops are rape and mustard, groundnut or peanut, sunflower, safflower, soybean, sesame, castor bean,
linseed, and flax.
Pulses or grain legumes. These crops belong to the family Leguminoseae and are grown for their edible seed. Chickpea or gram, pea, pigeonpea, cowpea or lobia, mung bean, mash bean, faba bean, field bean, lima bean,
and lentil are major leguminous crops.
Root and tuber crops. These are vegetable crops grown for underground parts like roots, bulbs, rhizomes, corms, and stem tubers, e.g. carrot, radish, turnip, onion, garlic, calocasia, and potato.
Narcotic or drug crops. This category includes those crops which have some narcotic or drug value, e.g. poppy, tobacco, tea, coffee, and peppermint. These are also known as medicinal crops.
Vegetable or garden crops. Vegetable crops which are grown for their edible leaves, shoots, flowers, fruits, and seeds. Asparagus, broccoli, cabbage, cauliflower, spinach, cucumber, pumpkin and squash, tomato, eggplant, and
okra or lady’s finger are grouped together as vegetable crops.
Condiment crops. Crops which are grown and consumed as condiments, e.g. coriander, mint, and chilies.
Special purpose classification
Sometimes certain crops are grown for specific purposes under various circumstances.
Green manure crops. Some crops are grown and plowed under in the green or mature form in order to improve soil fertility. These include dhain- cha, brassica, berseem, and guara.
Silage crops. These crops are cut and preserved as silage in a succulent condition by partial fermentation in silos. In Western countries, silage making is practiced by almost every dairy or beef cattle iarmer, while in Pakistan it is practiced mostly on military dairy farms. Crops used for silage are oat, maize, soybean, sorghum, and grasses. The resulting product is also known as haylage.
Soilage or green chop crops. These crops are harvested when still green and succulent and are fed directly to animals without curing, e.g. berseem, shaftal, and maize. This is also called soiling, zero grazing, or green feed.
Cover Crops. Some crops are planted to cover the ground and reduce soil erosion and nutrient losses by leaching.