Botany
KEY CONCEPTS I. Plant Parts II. Plant Processes III. Environmental Factors IV. Groupings of Plants Classification by life cycle Annuals Biennials Perennials Classification by Winter Leaf and Needle Loss Deciduous Evergreen Classification by Plant Growth Patterns Binomial Nomenclature Return to Introduction		IV. GROUPINGS OF PLANTS CLASSIFICATION BY LIFE CYCLE There are three groupings of herbaceous plants based on life cycle. ANNUALS Annuals are plants that can go through their entire life cycle, from seed germination to seed production and death, in one growing season. Common examples of annuals are corn, marigolds, zinnias, beans and California poppies. BIENNIALS Biennials are plants with a two-year growing cycle. The first year includes germination, leaf, root, compact stem and stored food production. The plant lives through winter. The second year it forms a vertical stem, flowers, fruits, and seeds. Then the plant dies. Examples of biennials are carrots, beets, onions, raspberries, hollyhocks, Sweet Williams and Canterbury bells. PERENNIALS Perennials are plants that live for many years, forming flowers and seeds each year. The above-ground parts may die back during winter and regrow in spring from the roots. Examples of perennials include delphinium, Stoke's aster, sedum, hosta, asparagus and strawberry.   CLASSIFICATION BY WINTER LEAF AND NEEDLE LOSS Woody plants are divided into deciduous and evergreen categories. DECIDUOUS Deciduous plants lose their leaves or needles in winter. Many shrubs fall into this group: spirea, forsythia, privet, lilac and mock orange. Examples of deciduous trees include fruit trees, buckeye, catalpa, maple, bald cypress and larch.   EVERGREEN Evergreen plants keep their leaves or needles year-round. Evergreens do drop old leaves or needles, but only those that are two or more years old. The autumn needle drop of pines often startles gardeners even though it is natural. Common evergreen shrubs and trees are pine, spruce, hemlock, yew, rhododendron, holly and azalea. The evergreen group includes two basic types: needle evergreens (spruce, hemlock, pine, yew and cypress) and broadleaf evergreens (rhododendron, holly, Oregon grape holly and mountain laurel).   CLASSIFICATION BY PLANT GROWTH PATTERNS The vascular (xylem and phloem) systems are different in certain groupings of plants. The vascular system of MONOCOTS has the conducting tubes scattered throughout the stem. In those plants grouped as DICOTS, the xylem and phloem are arranged in a ring. The arrangement affects the stem's ability to grow in girth. Monocot leaves are narrow with parallel veins, while dicots have broader leaves with net veining. Another distinction between monocots and dicots is the way the plant emerges from the seed. Monocots thrust up one seed leaf, and dicots push out two seed leaves. Monocots include grasses, sedges, lilies and onions. Dicots include trees, shrubs, most flowers and vegetables.   BINOMIAL NOMENCLATURE Horticulturists and serious gardeners use a two-name system to identify plants. This "scientific" or "Latin" name system is called binomial nomenclature. Many times gardeners use common names, but these can vary from person to person as well as region to region. The meaning of binomial nomenclature comes from breaking the word down into its roots: "bi" means "two" and "nomial" means "name." This is a universal naming system that also indicates relationships within groups of plants. The two names used in this system are the GENUS and SPECIFIC EPITHET. The genus name is always first and capitalized. The specific epithet is second and not capitalized. Together these two names describe the particular plant species. Genus is a cluster of plants with common characteristics that are easily recognized. Species is a group of plants that can generally interbreed only among themselves. They show persistent differences from members of closely related species. A good example of binomial nomenclature can be seen in maple trees. The scientific name for maple is "Acer" and many species of Acer are available for the gardener. They include the following: Acer campestre : Hedge Maple Acer japonicum : Japanese Maple Acer rubrum : Red Maple Acer saccharinum : Silver Maple Properly written scientific names are underlined or italicized. Binomial nomenclature gives many descriptive clues about the plant. It can indicate color, form, who discovered it or where it originated. It is worthwhile for the home gardener to become familiar with this binomial nomenclature because many excellent gardening magazines and reference books will refer to plants by their scientific names. Plants also are grouped together within a species. These subgroups are varieties and cultivars (cultivated varieties). A variety is a group of plants that developed a new characteristic through naturally occurring hybridization. Cultivars or cultivated varieties are new or hybrid plants that are hybridized by human manipulation. An example of a cultivar is Acer rubrum 'Red Sunset'. You occasionally may see it written Acer rubrum cv. Red Sunset.
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