Dry fruits that break open to free the seeds while still attached to the plant are described as dehiscent. Some examples are legumes (pea pod), which develop from a single ovary that splits down both sides and capsules that grow from a compound ovary and open at the top (poppy). The pericarp of indehiscent fruits remains closed until after it falls off the plant; examples of these types of fruits are corn and nuts.
species, made up of a generic name (the genus) plus a specific name that defines the species. It was developed by Carolus Linnaeus in the eighteenth century (Figure 2.3). Linnaeus built upon the work of many prior botanists. The earliest records made by the fathers of botany date from the fifth century B.c. to the third century a.d. and recount knowledge from Mesopotamia, Egypt, Greece, and Rome. Arab and Asiatic botanical records from the eighth to the twelfth century a.d. and the work of botanists from the 1500s to the 1700s were also described by Linnaeus.
Binomial nomenclature was created in Latin, as this was a language common to botanists from different countries. The genus name is a Latin noun that may be the name of a person who discovered the plant or it may somehow describe a common trait of all the plants in the genus. The species name is a Latin adjective that modifies the noun based on a particular characteristic of the species, such as the color of the flowers or size of the plant. The genus is always capitalized; the species name is in lowercase and the full name is either italicized or underlined. (For example, the binomial name for corn is Zea mays.) The genus can be abbreviated by the first letter followed by a period in instances where it has been previously referred to in a manuscript. Sometimes the specific epithet is designated as sp. or spp. (plural) in cases where it is either not known or if the writer wants to refer to all plants in the genus.
The binomial nomenclature, or Latin name, may be modified to reflect a botanical variety or a horticultural cultivar that is noticeably different from other plants of the same species (though all members of a species—including the unique varieties and cultivars—can interbreed). The modification accounts for differences that occur in plants because of growth in various types of soil or spontaneous mutations that may produce a different color flower or variegated leaves, among other traits.
Varieties are plant specimens identified in their natural environment, whereas cultivars are those that were cultivated and bred by man. However, many subspecies of vegetables are called
varieties and the two terms are often used interchangeably. The cultivar or variety name is set in single quotes, is not italicized, and is limited to three words. The cultivar name either follows the binominal or is used in place of the species name. Collections of cultivars may be combined into larger horticultural groups.
Examples of Latin names, followed in parentheses by the common name(s), for the culinary species of thyme include Thymus vulgaris (common thyme, garden thyme), T. herba-barona (caraway thyme, herb baron) and Thymus x citriodorus (lemon-scented thyme). The x in T. x citriodous is used to designate it as a hybrid. Hybrids are a result of cross-breeding as described in the next chapter. T. serpyllum 'Coccineus' (red creeping thyme) is not an edible plant but is appropriate for use in a garden path or rock garden because of its creeping habit and colorful flowers. The word 'Coccineus' set in single quotation marks indicates that it is a cultivar name.
Plants need to be described before they can be identified. Plant anatomical and morphological characteristics are used to generate descriptions of plants and to group them according to their similarities in order to identify and name them. The best times to describe plants are when they are in full flower. Alternately, fruiting structures will yield a great deal of information. The order of the description follows the growth of the plant. It begins with the roots, moves to the stem and leaves, and ends with a description of the reproductive structures (flowers and fruits).
Once these features have been noted, one can consult a botanical text with a dichotomous key, field guides, illustrated encyclopedias, seed and plant catalogs, garden centers, botanical gardens, and herbariums for descriptions of similar plants that have been previously identified and named. A dichotomous key consists of paired statements that describe the characteristics of a plant. One of the statements will apply to the plant and directs the user to another set of paired statements. This continues until the plant is named. Pictures, illustrations, or dried specimens can be very helpful in the identification of plants.
Dried specimens are made by pressing the whole plant between sheets of paper, then mounting with glue. Herbariums are collections of pressed, dried plants that have been identified by botanists and can be found in botanical gardens, at universities, and in private collections (Figure 2.4). Dried specimens can
be brought to an herbarium for identification by comparison to other plants in the collection.
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