Plant Classification

I. GENERAL TERMINOLOGY

1. By growth habit:

• Succulent plants - herbaceous or herbs (succulent seed plants possessing self-supporting stems)
• Vine - a climbing or trailing herbaceous plant (Liana - a climbing or trailing woody plant)
• Trees - having a single central axis
• Shrub - having several more or less upright stems

2. By leaf drops:

• Deciduous - no living leaves during dormant (winter) season (apple)
• Evergreen - retaining functional leaves throughout the year (spruce)

3. By life span:

• Annuals - plants that normally complete their life cycle during a single growing season (lettuce, spinach, marigold)
• Biennial - plant that normally completes its life cycle during a period of two growing seasons (celery, carrot, parsnip)
• Vegetative (often rosettes) during the first growing season. The winter following the first growing season provides the low temperature necessary to stimulate to 'bolt' or to send up a seed stalk during the second growing season. Carrots, radish and beets are harvested as annuals at the end of the first growing season after they develop over-wintering storage organs.
• Perennial - plants that grow year after year, often taking many years to mature.
  Unlike annuals and biennials, the perennial does not necessarily die after flowering (fruit trees; asparagus, rhubarb whose above ground parts are killed each year (in temperate regions) but roots remain alive to send up shoots in the spring; subtropical perennials such as tomato and eggplant are considered annual in temperate regions; Rubus (raspberries) has perennial roots and biennial shoots)

4. By temperature tolerance:

• Tender plant - damaged or killed by low temperature
• Hardy plant - withstands winter low temperatures
• Wood hardy - a whole plant is winter hardy
• Flower-bud hardiness - ability of flower buds to survive low winter temperatures (peach, ginkgo tree)

5. By temperature requirements:

• Cool-season crop - prefers cool temperatures (peas, lettuce, cole crops)
• Warm-season crop - prefers warm temperatures (tomato, pepper)

6. By habitat or site preference:

• Xerophyte - prefers dry sites
• Shade plants - prefers low light intensity
• Acid loving - prefers low pH soils
• Halophyte - prefers salty soils (in contrast to glycophyte - plants which are not salt-tolerant and are damaged fairly easily by high salinity)

II. HORTICULTURAL PLANT CLASSIFICATION

1. Edibles

A. Vegetables

Plants grown for aerial portions:

• Cole Crops (broccoli, cabbage, cauliflower)
• Legumes (bean, peas)
• Solanaceous fruit crops (Capsicum pepper, eggplant, tomato)
• Cucurbits or vine crops (cucumber, melon, squash, pumpkin)
• Greens or pot herbs (chard, dandelion, spinach)
• Mushrooms (Agaricus, Lentinus)
• Other vegetables (asparagus, okra, sweet corn)

Plants grown for underground portions:

• Root crops:
  Temperate (beet, carrot, radish, turnip)
  Tropical (cassava, sweet potato, taro, yam)
• Tuber crops (Jerusalem artichoke, potato)
• Bulb and corm crops (garlic, onion shallot)

B. Fruits

Temperate (Deciduous):

• Small fruits
  Berries (blueberry, cranberry, strawberry)
  Brambles (blackberry, raspberry)
  Vines (grape, kiwifruit)
• Tree fruits
  Pome fruits (apple, pear, quince)
  Stone fruits (apricot, cherry, peach, plum)

Subtropical and tropical (Evergreen):

• Herbaceous and vine fruits (banana, papaya, passion fruit, pineapple)
• Tree fruits
  Citrus (grapefruit, lemon, lime, mandarin, orange)
  Non-citrus (avocado, date, fig, mango, mangosteen)

C. Nuts

• Temperate (almond, chestnut, filbert, pecan, pistachio)
• Tropical (Brazil nut, cashew, macadamia)

D. Beverage Crops

• Seed (cacao, coffea)
• Leaf (tea, mate)

E. Herbs and Spices

• Culinary herbs (dill, rosemary, sage)
• Flavorings (peppermint, spearmint)
• Tropical spices (cinnamon, clove, nutmeg, pepper)

2. Ornamentals

A. Florist Crops

• Cut flowers (rose, carnation, chrysanthemum, alstroemeria)
• Flowering pot plants (geranium, poinsettia, Easter lily, gloxinia)
• Foliage plants (philodendron, ficus, aglaonema)
• Bedding plants (petunia, impatiens, marigold, zinnia)

B. Landscape Plants

• Trees
  Deciduous (maple, elm, aspen, oak, willow)
  Evergreen (pine, juniper, spruce)
• Shrubs
  Deciduous (lilac, azalea, privet)
  Evergreen (juniper)
• Vines (ivy, bougainvillea, pyracantha)
• Herbaceous perennials (penstemon, peony, columbine)
• Ground covers (ivy, vinca, juniper)

C. Lawn and Turf Plants

Bermudagrass, bluegrass, fescue, perennial ryegrass, buffalograss

3. Industrial Crops

• Drugs and Medicinals (digitalis, quinine, opium poppy)
• Oil Seeds (oil palm, jojoba, tung)
• Extractives and Resins (Scotch pine, Para rubber tree)
• Insecticides (pyrethrin, neam plant)

III. NOMENCLATURE (SCIENTIFIC PLANT CLASSIFICATION)

Early classification started by the Greek philosopher Theophrastus who classified all plants into annuals, biennials, and perennials according to life spans, and into herbs, shrubs, and trees according to their growth habits.



The modern taxonomy for plant classification is based on Linnaeus (a 18th century Swedish physician, now considered "father of taxonomy") who revolutionized the fields of plant and animal classification.

1. The Plant Kingdom

Kingdom Plantae
Division (Anthrophyta)
Class (Dicotyledonae)
Order (Rosales)
Family (Rosaceae)
Genus (Malus)
Species (pumila)
Variety
Form
Individual

Horticulture deals with mostly family, genus, species, and cultivars.

- Botanical names are binomial.
- Underline or italicize genus and species: Genus species (or Genus species)
- Do not underline the family and cultivar names: Rosaceae, Golden Delicious
- Variety names may be underlined.

Examples:
Juniperus communis var. depressa (Prostrate Juniper)
Malus domestica cv. Red Delicious (Red Delicious Apple)
Malus domestica 'Red Delicious' (Red Delicious Apple)
Malus pumila cv. Red Delicious (Red Delicious Apple)

2. Some frequently used terms

Variety - a group of variants within a species which have similar characteristics.
Cultivar - cultivated variety
Ecospecies - a subdivision of species that are formed by ecological barrier. i.e., Cercis canadensis (Redbud)
Clone - a group of plants all of which arose from a single individual (the ortet) through asexual propagation.
Clonal cultivar - asexually propagated clones (potato, rose, etc.).
Pure line cultivar - homozygous inbred lines grown from seed.
Hybrid cultivar - a cultivar composed of hybrids between genetically diverse parental lines uniform phenotype, genetically heterozygous)

A botanical name (binomial name) is a formal scientific name conforming to the International Code of Nomenclature for algae, fungi and plants (ICN) and, if it concerns a plant cultigen, the additional cultivar and/or Group epithets must conform to the International Code of Nomenclature for Cultivated Plants (ICNCP). The purpose of this name is to have a single name that is accepted and used worldwide for a particular plant or plant group.

Examples of names governed by the ICN for Cultivated Plants:
Clematis alpina 'Ruby' : a cultivar within a species; the cultivar epithet is in single quotes and capitalized.
Magnolia 'Elizabeth' : a cultivar within a hybrid between two or more species.
Rhododendron boothii Mishmiense Group : a Group name; both the name of the Group and the word "Group" are capitalized and not enclosed in quotes.
Paphiopedilum Sorel grex : a grex name; the name of the grex is capitalized but the word "grex" (if present) is not and quotes are not used.
Apple 'Jonathan' : permitted use of an unambiguous common name with a cultivar epithet.
+Crataegomespilus : a graft-chimaera of Crataegus and Mespilus.

In scholarly texts, at least the first or main use of the binomial name is usually followed by the "authority" a way of designating the scientist(s) who first published the name. The most valuable initial function of author citations in biology is probably to distinguish between homonyms, in other words taxa which coincidentally share the same name but in fact represent different entities. In botany, it is customary (though not obligatory) to abbreviate author names according to a recognised list of standard abbreviations (Rubus ursinus Cham. & Schldl. or Rubus ursinus Cham. et Schldl. or Rubus ursinus von Chamisso & von Schlechtendal or Rubus ursinus von Chamisso et von Schlechtendal).

The multiplication symbol (not italicised) indicates a hybrid in the Latin binomial nomenclature.
Placed before the binomial it indicates a hybrid between species from different genera - intergeneric hybrid:
Fatshedera lizei, a hybrid between Hedera helix and Fatsia japonica
For Interspecific plant hybrids the multiplication sign goes before the epithet:
Dianthus allwoodii, a hybrid between Dianthus caryophyllus Dianthus plumarius
The hybrid may get a normal botanical name for naturally occurring hybrids:
Iris albicans, a sterile hybrid which spreads by rhizome division.

In botany, the correct name according to the International Code of Nomenclature for algae, fungi, and plants (ICN) is the one and only botanical name that is to be used for a particular taxon, when that taxon has a particular circumscription, position and rank. If there are two or more legitimate names for the same taxon (with the same circumscription, position and rank), then the correct name is the one which has priority, i.e., it was published earliest, although names may be conserved if they have been very widely used. Validly published names other than the correct name are called synonyms.
The correct name has only one correct spelling, which will generally be the original spelling (although certain limited corrections are allowed). Other spellings are called orthographical variants.

See also Plants Dictionary