Plant Structures: Flowers

pdf logoPrint this CMG GardenNotes

green line
green line

questionThought Questions

Explain the science behind the following gardening questions:

1, My zucchini is blooming but doesn’t set any fruit.  Why??



green line

Flowers are the reproductive structures of a flowering plant.  Flowers are the primary structures used in grouping plant families.

Function

  • Reproduction, beginning with pollination and fertilization.
  • Advertisement and rewards to lure a pollinator.
  • Horticultural uses
  • Aesthetic qualities
  • Cut flowers and potted blooming plants
  • Edible flowers and herbs
  • Plant identification

Structure

  • Pistil – Central female organ of the flower.  It is generally bowling-pin shaped and located in the center of the flower.

  • Stigma – Receives pollen, typically flattened and sticky
  • Style – Connective tissues between stigma and ovary
  • Ovary – Contains ovules or embryo sacs
  • Ovules – Unfertilized, immature seeds

  • Stamen – Male flower organ

  • Anthers – Pollen-producing organs
  • Filament – Stalk supporting anthers

  • Petals – Usually colorful petal-like structures making up the “flower”, collectively called the corollaThey may contain perfume and nectar glands. 

  • Sepals – Protective leaf-like enclosures for the flower buds, usually green, collectively called calyx.  Sometimes highly colored like the petal as in iris.

  • Receptacle – Base of the flower

  • Pedicel – Flower stalk of an individual flower in an inflorescence

Parts of a flower
Figure 1. Parts of a flower


Monocot or Dicot Flower

The number of sepals and petals is used in plant identification.  Dicots typically have sepals and petals in fours, fives, or multiples thereof.  Monocots typically have flower parts in threes or multiples of three.

Monocot and dicot flowers

Figure 2. Monocot and dicot flowers.


Terms Defining Flower Parts

  • Terms referring to flowers

  • Complete – Flower containing sepals, petals, stamens, and pistil
  • Incomplete – Flower lacking sepals, petals, stamens, and/or pistils

  • Perfect – Flowers containing male and female parts
  • Imperfect – Flowers that lack either male or female parts

  • Pistillate  – Flowers containing only female parts
  • Staminate – Flowers containing only male parts

  • Terms referring to plants

  • Hermaphroditic – Plants with perfect flowers  (apples, tulips)
  • Monoecious – Plants with separate male flowers and female flowers on the same plant  (corn, squash, and pine)
  • Dioecious – Plants with male flowers and female flowers on separate plants  (maple, holly, and salt brush)

  • Gynoecious – Plants with only female flowers
  • Andromonoecious – Plants with only male flowers

Inflorescence (flower arrangement on a stem)

  • Catkin – A spike with only pistillate or staminate flowers (alder, poplar, walnut, and willows)

  • Composite or Head – A daisy-type flower composed of ray flowers (usually sterile with attractive, colored petals) around the edge and disc flowers that develop into seed in center of the flat head (sunflower and aster)  On some composites, the ray and disc flowers are similar (chrysanthemums and dahlias)

  • Corymb – Stemlets (pedicels) arranged along main stem.  Outer florets have longer pedicals than inner florets giving the display a flat top. (yarrow, crabapple)

  • Cyme – A determinate, flat or convex flower, with inner floret opening first. 

  • Panicle – An indeterminate flower with repeated branching.  It can be made up of racemes, spikes, corymbs, or umbels.  (begonia)

  • Raceme – A modification of a spike with flowers attached to a main stem (peduncle) by stemlets (pedicel). (snapdragon, bleeding heart, Canterbury bells)

  • Solitary (or single) – One flower per stem  (tulip, crocus)

  • Spadix – Showy part is a bract or spathe, partially surrounding the male and female flowers inside.  (calla, caladium)

  • Spike – Flowers attached to main stem, without stemlets, bottom florets open first.  (gladiolus, ajuga and gayfeather)

  • Umbel – Florets with stemlets attached to main stem at one central point, forming a flat or rounded top.  Outer florets open first.  (dill, onion)

  • Symmetrical – Symmetrical flowers  (lily)

  • Asymmetrical – Asymmetrical flowers  (snapdragon)

Flower Inflorescence

Figure 3. Types of inflorescence (flower arrangement on stem)



green line
green line

Authors: David Whiting (CSU Extension, retired) with Michael Roll and Larry Vickerman (former CSU Extension employees). Artwork by Scott Johnson and David Whiting.

  • CMG GardenNotes are available online at www.cmg.colostate.edu
  • Colorado Master Gardener/Colorado Gardener Certificate Training is made possible by a grant from the Colorado Garden Show, Inc.
  • Colorado State University, U.S. Department of Agriculture, and Colorado counties cooperating
  • Extension programs are available to all without discrimination.
  • Colorado Master Gardener LogoNo endorsements of products mentioned is intended nor is criticism implied of products not mentioned.
  • Copyright. 2003-14. Colorado Master Gardener Program, Colorado State University Extension. All Rights Reserved. CMG GardenNotes may be reproduced without change or additions, for nonprofit educational use.

Revised October 2014

green line