Plant Biology

Understanding the biology of invasive plants is a fundamental part of invasive plant management. The biology of these species can teach us lots of things. With this information you can learn to identify these and other plants and why some plants become invasive. You can also better anticipate where certain invasive plants are more likely to be found. It can also help us understand which and why different control methods work best for each species.

Plant Life Cycle

The time it takes a plant to grow from seed to mature plant


Plants that germinate, reproduce, and die in one growing season

Cool season annuals: grow during the coldest parts of the growing season and can withstand frost. Two flushes, or crops, of these species are possible each year (spring and fall). Example: cheatgrass

Warm season annuals: grow during the warmer parts of the growing season and are not tolerant of heavy frost. Example: common sunflower

Cool season annual - Cheatgrass


Plants that complete their life cycle in two growing seasons.

  • During the first growing season only vegetative parts grow. Plants go dormant and may appear to die over winter.
  • During the second year reproductive parts are produced. The plant dies at the end of the second growing season. Example: musk thistle
Biennial - Musk Thistle


Plants that grow for more than two growing seasons.

Herbaceous perennials: have soft, nonwoody stems that may die back each year (note: while the dead stems or “carcass” may remain, new stems are produced each year). Example: common tansy

Woody perennials: have woody stems that do not die back. Examples: aspens and lodgepole pine

Herbaceous perennial - Common Tansy

Reproduction Strategies

How a plant makes new plants. Many invasive plants use both sexual and asexual reproduction. Sexual reproduction allows seeds to be spread to other areas while asexual reproduction allows invasive plants to form dense stands.


Reproduction through seeds or spores

Asexual or Vegetative

Plants create new plants from pieces of themselves

  • Roots: sprouting occurs spontaneously or by injury to roots. Example: Russian olive
  • Rhizomes and Stolons: modified stems that form new plants.
    - Rhizomes
    : underground. Examples: Canada thistle and oxeye daisy
    - Stolons
    : above ground. Example: strawberries
  • Tubers and Bulbs: modified, underground parts that can be divided to create new plants.
    - Tubers
    : modified stems with buds that produce new shoots. Example: potatoes
    - Bulbs
    : modified leaves that produce a shoot. Example: onions
  • Stem fragments or cuttings: cutting or fragmenting of a stem produces a new plant. Example: Redosier dogwood

Dispersal Mechanisms

How seeds and reproductive parts are moved

Wind: seeds may be winged or tufted. Examples: maple trees and dandelions 

  • Water: seeds are lightweight or buoyant. Examples: perennial pepperweed and Russian olive
  • Animals: seeds are contained in or on fruit that is edible to animals or have hooks/barbs that attach passersby. Examples: snowberry and houndstongue
  • Explosion: seeds are contained in pods that burst open flinging seeds away from the parent plant. Examples: lupine and leafy spurge
  • Humans: whether intentional or accidental, humans are responsible for spreading many plant species including native, beneficial, ornamental, and invasive species.

- Intentional: spreading seeds and plants for agricultural, ornamental, or other uses by humans. Examples: apple trees, Kentucky bluegrass, and dyer’s woad
- Contamination: seeds or plants can be moved in seed mixes or root balls of plants
- Carried: seeds with barbs/hooks can be moved on clothing and gear; seeds and reproductive parts in mud can be moved on equipment and shoes; and seeds and reproductive parts can be moved in other materials like packing materials.
- Disturbance: tilling or moving soil can spread or unearth seeds and reproductive parts.

Identifying Characteristics

Growth Habit

The general shape or form a plant takes under normal growing conditions.

  • Prostrate: grows flat along the ground
  • Spreading ascending: grows flat along the ground but tips grow upward
  • Erect shrub: grows from a single stem that is heavily branched or clump of stems
  • Erect or columnar: grows from a single stem with little or no branching
  • Vine: may be climbing or twining and is not self-supported

Leaf Arrangement

how leaves are arranged on the stem.

  • Alternate- one leaf occurs at each node, alternating sides up the stem
  • Opposite- two leaves occur at each node or in pairs up the stem
  • Basal- leaves occur in a whirl or clump at the base
  • Whorled- three or more leaves occur at each node

Leaf Shape

The shape of the entire leaf from the stem node


Consists of a single blade connecting to the stem. May be divided, but does not have leaflets

  • Linear- long and thin but generally uniform
  • Lanceolate- long and thin. Flat and wide at base and narrowing toward tip.
  • Oblong- long and wide but generally uniform
  • Eleptic- long and thin. wider at base
  • Oval- long but generally oval shaped
  • Ovate- long and rounded. Base is wider than tip.
  • Obovate- long and rounded. Tip is wider than base.
  • Reniform- kidney-shaped
  • Cordate- heart-shaped
  • Sagittate- arrowhead
  • Lyrate- lobed with largest lobe at the tip
  • Pinnately lobed- indented equally along the mid-vein
  • Palmately lobed- indented toward a central point

Made up of two or more distinct leaflets that connect to the stem.

  • Palmate- leaflets are whirled and attached at a central point
  • Pinnate- leaflets occur in pairs up the petiole. Some plants have a terminal leaflet giving them an odd number. Leaves may also be bi or tripinnately compound.

Leaf Margin

The edge of the leaf or leaflet

  • Entire- margin is smooth and uninterrupted
  • Serrate- pointed teeth with points facing toward tip
  • Crenate- scalloped or rounded teeth
  • Dentate- pointed teeth with points facing outward
  • Lobed- deep indentations toward midrib or central point
  • Undulate- wavy or curling


How flowers occur on the plant 

  • Solitary- flowers occur singly. May be terminal or along the stem.
  • Spike- flowers are attached on an elongated stem
  • Raceme- flowers are attached on short stalks to an elongated stem
  • Umbel- flowers are attached on short stalks that emerge from a common point
  • Panicle- a raceme that is branched or compound
  • Cyme- a cluster of flowers where the first flower to open is the the top or middle
  • Corymb- a raceme where the flower stalks are different lengths creating a flat topped or rounded shape
  • Head (capitulum)- dense clusters of flowers do not have stalks

Root Type

Structure of the root system including modified stems

  • Taproot- a single primary root that grows downward. Root hairs may be present.
  • Fibrous- thin, heavily branched roots originating from a central point.
  • Rhizomatous- underground, modified stems that produce new shoots
  • Stolons- horizontal, above ground stems that root and produce new shoots
  • Bulbs- modified leaves that store nutrients
  • Corms- modified stems that store nutrients
  • Tubers- modified stems that store nutrients

Identification Tools

The identification characteristics above can help you identify or narrow down which species of plants you have. You can use the tools below to confirm or pinpoint which species you have.

Smartphone Photos

iOS and Android systems can conduct a photo search from the photos you take. For both systems, start by taking a clear photo of the plant in question then follow the steps below for each type of device. You will need to be within cellular service or connected to wifi.

  • In the Photos app, click on the photo.
  • If the i icon has two stars, click to see photo information.
  • Click “Look Up - Plant” to have Siri conduct a photo search.
  • In the Photos app, click on the photo.
  • Tap the “Lens” feature to conduct a Google photo search.
Smartphone Apps:

Tried all the options and still stuck?

You can submit a clear photo of the plant to us using our Invasive Plant ID form.