Plant Classification

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Plant Classification

• Objectives of todays lecture
• learn some common terms used to group plants
• learn the scientific protocols used to name
  plants so they can be universally recognized
• learn about the terminology used to distinguish
  plants within a species

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Categorizing plants is an ancient practice

• The Greek philosopher Theophrastus (300 B.C.E.)
  published the first horticulture text book
  Historia Plantarum. In this text, plants are
  grouped together based on life span, growth
  habit, retention of leaves, and other traits
• Many of these characteristics are still used to
  classify plants

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Categorizing plants

• Thousands of plants are used today in various
  areas of horticulture
• Convenient to group plants together based on
  common characteristics
• life cycle
• growth habit
• environmental adaptation
• end use or function

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Classification based on life cycle

• Annuals
• plants that complete their life cycle (from seed
  to seed) in 1 year, e.g. petunia, peas

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Classification based on life cycle

• Biennials
• plants that require all or part of two growing
  seasons vegetative growth in the first year,
  followed by overwintering (low temperature)
  biennials flower in the second growing season,
  e.g. hollyhocks, carrot

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Classification based on life cycle

• Perennials
• plants that persist for more than two seasons and
  do not die after flowering, e.g. maple,
  forsythia, tulips, daylily

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Classification based on life cycle

• Note that many biennials and perennials are grown
  as annuals
• root crops such as carrots and beets are grown
  and harvested in one season, before they flower
• tomatoes and poinsettias are grown in the US as
  annuals, but in S. America they grow as perennials

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Classification based on growth habit

• Normally applied to perennial plants
• Woody plants
• have persistent vegetative structures, e.g. trees
  and shrubs

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Classification based on growth habit

• Herbaceous perennials
• do not have woody structures and vegetation does
  not persist, e.g. daylily, hosta

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Classification based on growth habit

• Vines
• climbing or trailing plants that require support,
  e.g. grapes, wisteria, clematis

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Classification based on growth habit

• Deciduous plants
• shed leaves for part of the year
• Evergreens
• never without leaves
• they still shed leaves or needles after new
  organs are formed

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Classification based on environmental adaptation

• Temperature
• Hardy, tolerant of low temperatures
• Tender, unable to survive low temperatures
• Warm season crops, e.g. corn, beans, melon
• Cool season crops, e.g. lettuce, peas, broccoli

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Classification based on environmental adaptation

• Temperature
• USDA hardiness zone map

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Classification based on environmental adaptation

• Requirement for water
• Aquatic plants, which live in water
• Xerophytes, which require very little water
• Soil conditions
• Halophytes are adapted to salty conditions
• Acidophytes require acid soils, e.g.
  rhododendrons
• Metallophytes require high levels of specific
  metals

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Classification based on usage

• Edible plants
• fruits (dessert or snack)
• vegetables (savory)
• Note that this classification differs from the
  botanical definition of a fruit. The strict
  botanical definition of a fruit is a structure
  that develops from the ovary in a flower. Using
  this definition, a tomato is a fruit while a
  strawberry is not.

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Classification based on usage

• Other culinary uses include
• nuts (hard seeded fruits)
• herbs (fresh or dried vegetative tissue)
• spices (dried fruit or bark)
• beverages (tea and coffee)
• Medicinal plants
• source of pharmaceuticals, e.g. digitalis from
  foxglove, taxol from a yew

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Classification based on usage

• Industrial plants
• provide raw materials for industrial use
• oils from oil palm or jojoba
• fibers from flax or hemp

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Classification based on usage

• Ornamental uses
• nursery crops, e.g. trees and shrubs
• ground covers, e.g. ivy and pachysandra
• bedding plants, e.g. petunias and pansies
• foliage plants, for indoor decoration
• pot crops, e.g. poinsettia and chrysanthemum
• floriculture crops, e.g. roses and carnations

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Limitations of these classification systems

• Classifications are very subjective
• Based on your perspective, a hazel shrub can be
  regarded as a source of nuts, an ornamental
  landscape shrub, or a weed.
• What is grown as an annual in one region is
  classified as a perennial elsewhere.
• Plants that are considered hardy in Florida or
  Georgia are considered tender in Indiana.

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Limitations of these classification systems

• These classifications are not understood
  throughout the world, in different languages or
  across cultures
• Common names can be confusing
• Same name used to describe different plants
• Different names to describe the same plant

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Scientific classification system

• Advantages of this system include
• common universal designation
• based on international convention
• uses Latin, a dead language that will not
  change
• All organisms are divided into a series of
  categories called taxa

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Scientific classification system

• Kingdom (plant, animal, bacteria, etc.)
• Division
• Class
• Order
• Family
• Genus
• Species
• Members of each successive category are more
  similar to each other

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Scientific classification system

• Developed by Carl von Linne, a Swedish physician.
  He is better known as Linnaeus, the father of
  taxonomy
• In 1753, Species Plantarum was published ,
  which described his new classification system

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Scientific classification system

• Linnaeus system of classification is based on
  stable morphological features, especially flowers
• Avoids features that can vary with age of the
  plant or the environment in which the plant is
  grown
• Incorporates the concept of evolution, i.e.
  plants with similar features share a common
  ancestor

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The Binomial System

• Each name has two components
• Genus specific epithet species
• Prunus persica (peach)
• belongs to the Genus Prunus
• species name is Prunus persica
• Conventions that apply to this system
• written in italics (or underlined)
• first letter of the Genus is capitalized

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The Binomial System

• Genus - a group of similar organisms, some of
  which may interbreed
• Species - members will interbreed and produce
  similar progeny
• No matter your origin or situation, Solanum
  tuberosum is recognized as referring to pomme de
  terre, kartoffel, potato

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The Binomial System

• Avoids confusion that can arise when using common
  names

Rose of Sharon
Rose of Sharon
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Additional terms used with the binomial

• Prunus persica (L.) Batsch
• (L.) indicates the authority, the individual
  who first named this species
• Linnaeus is indicated by (L.)
• Others are written out in full
• Amendments to the classification are added after
  the authority, e.g. Batsch

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Additional terms used with the binomial

• Botanical varieties
• Juniperus communis var. depressa
• Indicates a botanical variety within this species
  of juniper, in this case plants with a
  distinctive low-growing (depressed) habit

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Additional terms used with the binomial

• Interspecific hybrids
• Forsythia X intermedia
• X indicates these plants result from a cross
  between two different species (F.suspensa and F.
  viridissima) in the genus Forsythia

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Additional terms used with the binomial

• Prunus persica cv. Redhaven
• cv. Redhaven indicates a cultivar
• Also written as Prunus persica Redhaven
• single quotation marks indicates the cultivar
• Cultivars are cultivated varieties
• Cultivars are groups of plants within a species
  that share common characteristics and maintain
  their identity

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Summary

• Many different methods used to classify plants
  used in horticulture
• The scientific binomial system provides a
  universal protocol that does not depend on
  variable factors