Plant Taxonomy


Plant Origin & Classification
All Materials © Cmassengale


Overview of Plants:

  • All plants are multicellular & contain chlorophyll inside of chloroplasts
  • Plants (also called autotrophs or producers) trap energy from the sun by photosynthesis & store it in organic compounds
  • Heterotrophs or consumers get their energy directly or indirectly from plants
  • Plants also release oxygen needed by consumers
  • All plants are multicellular, eukaryotic organisms that reproduce sexually
  • Many medicines are produced by plants
  • Plants are very diverse & may be terrestrial or aquatic
  • Vary in size from 1 mm in width to more than 328 feet
  • May live a few weeks or some over 5000 years
  • Kingdom Plantae is divided into 12 phyla or Divisions
  • More than 270,000 plant species identified, but new species still unidentified in tropical rain forests

Terrestrial Adaptations:

  • Plants probably evolved from green algae

  • Both algae & plants have chlorophyll a & b, have cell walls made of cellulose, and store energy as starch
  • First land plants had to develop adaptations to scarcity of water & climate changes (air temperature changes more rapidly than water temperature)
  • Moving onto land allowed more sunlight, nutrients,  & CO2 for photosynthesis
  • A support adaptation included a compound called lignin (a hard substance that strengthens cell walls so they can support additional weight)
  • The origin of vascular tissue (specialized tissue for carrying food , water, & minerals) was an evolutionary breakthrough in the colonization of land
  • Plants with vascular tissue are known as Tracheophytes
  • Two types of vascular tissue developed — xylem & phloem

  • Xylem carries water & inorganic nutrients from the roots to the stem & leaves
  • Phloem carries carbohydrates made by the plants to wherever they’re needed or stored in the plant

Copyright Holt, Rinehart, & Winston

  • Some plants formed woody tissue from xylem for extra support, while others kept a flexible, non-woody stem (herbaceous plants)
  • Greater amount of water lost by evaporation (transpiration) on land
  • A waxy covering or cuticle developed on all plant parts exposed to air which slowed transpiration (water loss)

  • Gases (carbon dioxide & oxygen) had to be able to move into & out of the plant
  • Openings in the cuticle called stomata allowed movement of gases
  • Two guard cells on each side of a stoma helped open & close the opening

Copyright Holt, Rinehart, & Winston

  • When guard cells lose water & shrink, the stoma closes (prevents water loss in the hotter times of the day)
  • When guard cells swell with water, the stoma opens for gas exchange 

copyright McGraw-Hill

  • Other structural adaptations to land included roots for absorption of water and minerals leaves for gas exchange and photosynthesis

Reproductive Adaptations:

  • To be successful on land, plants had to develop protective seeds for their embryos with stored food or endoderm

Copyright Holt, Rinehart, & Winston

  • Seeds are better at dispersal than spores

Classification of Plants:

  • They’re are 12 Divisions of plants divided into two main groups based on the presence of vascular tissue
  • Nonvascular plants lack vascular tissue and do not have true roots, stems, or leaves (mosses, liverworts, & hornworts)
  • Most plants have vascular tissue with true roots, stems, & leaves, but may or may not produce seeds

Copyright Holt, Rinehart, & Winston

  • Ferns, horsetails, & club mosses are seedless vascular plants that reproduce by spores
  • Plants that reproduce by seeds are divided into 2 groups — gymnosperms & angiosperms
  • Gymnosperms have “naked” seeds usually protected by cones & includes pines, cedars, spruce, fir …

  • Angiosperms are flowering plants whose seeds are produced & protected within the fruit

Plant Life Cycles:

  • Plants have 2 phases in their life cycle called alternation of generation
  • The haploid gametophyte stage produces eggs & sperm, while the diploid sporophyte stage produces spores 

Copyright Holt, Rinehart, & Winston

  • Plant gametes are not directly produced by meiosis but rather by mitosis from the haploid multicellular stage
  • Meiosis instead produced specialized haploid cells called spores
  • These spores are released by most Seedless plants, but are retained by Seed plants
  • In nonvascular plants, the Gametophyte stage is dominant (mosses)

  • In vascular plants, the Sporophyte stage is dominant
  • Seedless vascular plants usually have a separate, small gametophyte plant
  • Sexual reproduction in plants ensures that there will be genetic recombination

Seed-Bearing, Vascular Plants:

  • The development of seeds with their protected embryo & stored food supply increased the reproductive success of seed plants
  • Seeds remain dormant or inactive when conditions aren’t favorable
  • Moisture & warmer temperature cause seeds to germinate or sprout
  • Young plant embryos use their endosperm as energy for early growth

  • Seeds plants are divided into 2 groups based on  the type of seed they produce


  • Gymnosperms  produce seeds that not protected within an ovary
  • The seeds are exposed on the upper surfaces of a spore producing structure (e.g. cone scales in conifers)
  • Called “naked” seeds
  • Gymnosperms do not produce flowers or fruit
  • The four phyla of gymnosperms alive today include the cycads (Cycadophyta), the ginkgo (Gingkophyta), the gnetophytes (Gnetophyta), and the conifers (Coniferophyta)


GingkoFir Tree


  • All gymnosperms have vascular tissue to conduct food, water & minerals and produce woody tissue
  • Two types of cones are made by gymnosperms — pollen cones & seed cones
  • Pollen cones are small & produce pollen containing the male gametophyte which is spread by wind or insects to the female gametophyte
  • Seed cones are larger and contain eggs on scales that form seeds when they are fertilized

Division Cycadophyta:

  • Dominated earth when dinosaurs lived, but only about 100 species are alive today & are endangered
  • Most are slow growing, palm-like plants found mostly in tropical areas
  • All cycads bear cones, which are made up of seed bearing leaves (sporophylls)
  • They have large compound leaves, a short thick trunk, and are dioecious (either male or female plant)
  • Cycads bear naked seeds

Zamia (native to Georgia)

Division Gingkophyta:

  • Ginkgoes were common in the Mesozoic period,  but today only one species of ginkgo remains (Ginkgo biloba)
  • Gingko trees have distinctive fan shaped leaves & are dioecious (each tree is either male or female but not both)
  • Commonly planted as an ornamental tree
  • Gingkoes are not native to North America (they are found growing wild only in China)
  • Deciduous tree (loses leaves in fall) with plum-shaped, fleshy seeds with a foul odor

Division Coniferophyta:

  • Largest group of gymnosperms
  • Called conifers 
  • Found in abundance in temperate zones
  • Include cedars, pines, spruce, fir, juniper, & bald cypress trees
  • Their leaves are characteristically needle-like, but may be scale-like
  • Usually trees or shrubs
  • Evergreens (don’t lose their leaves in the fall)
  • Almost all conifers are monoecious, producing both male and female cones on the same tree
  • Female cones are larger than male cones with woody scales containing the seeds


Pollen ConeSeed Cone


  • Conifers are dependent on the wind for pollination
  • Pollen grain has air bladders to help it stay aloft in the wind
  • Important source of wood, paper, turpentine, ornamental plants, Christmas trees
  • Redwoods and Giant Sequoia trees are the largest living organism on earth
  • Bristlecone pines are the oldest living organism on earth


Redwood TreeBristlecone pine Tree


Division Gnetophyta:

  • The phylum Gnetophyta consists of 3 genera that are not very closely related
  • Ephedra is the largest genus and consists of plants that resemble horsetails & grow in deserts
  • Welwitshcia is found only in the desert area of south western Africa and has 2 single, long leaves




Division Anthophyta (Angiosperms):

  • Flowering plants are the most successful group of plants today
  • They live in almost all possible habitats
  • All flowering plants produce both flowers & fruit

  • Fruit is a ripened ovary with its seeds (acorns, apples, dandelion seeds, etc)

  • Flowering plants co-evolved with their insect pollinators
  • May be herbaceous (grasses & snapdragons or woody (oaks & grape vines)
  • Rafflesia, the stinking corpse lily, is the world’s largest flower

  •  Flowering plants have diverse lifestyles (Sundew is carnivorous on insects; Spanish moss is an epiphyte living on another host plant; some orchids are saprophytes living on soil fungi)
  • Subdivided into 2 classes based on the number of seed leaves or cotyledons in the plant embryo — Monocotyledons & Dicotyledons
  • Monocots have a single seed leaf, leaves with parallel venation, vascular tissue scattered in bundles throughout the stem, and flower parts in 3’s or multiples of 3

  • Dicots have a 2 seed leaf, leaves with net-veined venation, vascular tissue in rings in the stem, and flower parts in 4’s or 5’s multiples of 4 or 5

  • Monocots are usually herbaceous, while dicots often produce wood