Floral Structures

Probably the most interesting aspect of botany, or plants in general are the flowers. It isn’t hard to understand why, as they are used to decorate lawns, gardens, and our homes. Understanding flowers and floral structure are integral to us understanding how plants reproduce. Because let’s face it, without the flowers there wouldn’t be many species of plants in the world.

Furthermore, being able to differentiate small details in inflorescence can be very important when trying to identify flowers that are in bloom. Sometimes there are only tiny details on a flowerhead that can separate species (see Ironweed for example). And these tiny details can be incredibly interesting.

In this section I will attempt to show you some of the different bloom structures you may encounter, and to provide you with some example blooms from my own collection that will hopefully help you in understanding.

Glossary of floral terms

antherPart of a stamen that holds pollen
awna tiny bristle on an organ on grasses
axileplacenta on the central axis of an ovulary with at least 2 cells
berrya fruit with fleshy walls containing many seeds
bracta small, reduced or tiny leave often located at the base of flowers, on the backside of flower heads
bristlea slender hair on the surface,edges, or top of an organ.  Usually stiff/strong relative to it’s size
BulbA swollen structure made up of layers, like an onion
calyxThe outer parts of a flower made up of sepals
capsulea dried fruit with seeds.  They split open when mature
carpela single pistil or part of a compound pistil
central placentationSeeds and ovules on a central axis in a pistil (1-celled)
ciliatewhen something is marginally fringed with spreading hairs.
columnwhen multiple stamens are fused together.  Normally occurs in orchids or Mallow family
compound pistil2 or more carpels that are united
connectiveextra length of filament between or beyond two pollen sacs of the stamen
cormA short, thick portion of underground base of a vertical stem scales or leafless.  Similar to a bulb, but solid.
corollaAll petals of a flower combined
corymba flowerhead that is flat-topped or rounded.  Flowers with at the outermost places open first
cymea grouping of flowers broad in shape where the terminal flower of the cluster blooms first
disc flowerA flower without rays/petals in the Asteraceae family
female flowerA flower with pistils, but no stamens that bear pollen
filamentthe thin part of the stamen below the anther
herba plant that herbaceous, annual, biennial, or perennial.  The stems/stalks will die back to ground in Winter
hypanthiumA cup-shaped or saucer-shaped organ beneath the ovulary.  Sepals, petals, and stamens are attached near the edges of the hypanthium
inflorescenceA complete flower cluster including bracts or axis.  
Involcurebracts that are beneath, below, or around a single flower or head of flowers
irregularflowers that are of different shapes but of the same set or sets
legumea fruit that opens along the top and bottom edges containing seeds.  In the pea or Fabaceae family
liguleA flat, but petal like part of some corollas common to the Asteraceae family
lipThe upper or lower part of the corolla / calyx of flowers of the mint family.  Also the loest or odd petal in Orchids.
Male FlowerA flower with stamens but no functional pistil
ocreastipule that is tubular in shape around the stem of a node
ovularyThe part of the pistil that contains the ovules (future seeds).
paniclea flower cluster that rebranches, of the raceme type
papilionaceousHave keel petals and wings, like the corolla of some pea flowers
pappushairs, scales, or bristles that grow from the top of achenes that represents the calyx.  Common on the Asteraceae.
pedicelThe individual stalk of a flower (single flower)
peduncleThe main flower stalk that contains a single or cluster(s) of flowers
perfectused to describe flowers that have stamens and pistils that are both functional
perigyniumA bract that encloses that achene and pistil of a carex
petalone section of the corolla, separate or united.
phyllariesbracts that surround a single flower in the Asteracea family (composite family)
pistilthe center organ of a flower that contains the ovules
pistillateWhen a flower has pistils but no pollen-bearing stamens
pricklea sharp, ‘prickly’ feature on the outside edge of some stems, flowers, or bracts
racemeA series of single flowers on their own stalks attached along a common axis
receptaclethe common component that joins flower to flower stalk
regularflowers in a set that are of equal size
sepalpart of the calyx 
spathea large bract that frequently encloses inflorescence.  This only applies to monocotyledons.
Spikea type of flower cluster where you have flowers attached to a common axis without any stalk
spura tubular or sac-like extension of a part of a flower
stamenthe organ of a flower that makes pollen.  It is generally made up of an anther & filament
staminateWhen a flower has stamens and no functional pistil
stigmaThe part of a pistil that receives pollen
stylethe part of the pistil between the stigma and ovluary. This is where pollen gets transferred to the ovary
umbelA cluster of flowers where the stalks rise to a point, similar to the rib of an umbrella.  Can be single or compound.
unisexualwhen a flower has only stamens or only pistils
Sources [1] [2] [3] [4] [5]

How a flower gets pollinated

In the diagram at right, the pollen is dispersed from a the anthers. This gets transferred to the stigmas (often by bees), where the pollen is received. Pollen then travels through the ‘style‘ to the ovary, where ovules are present, and become fertilized. [1]

A fertilized flower will produce a viable seed.

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Flowers are pollinated be several ways:

  1. Pollinated by wind
  2. Pollinated by bees, butterflies, or other pollinating insects
  3. Self-pollination by wilting

Self Pollination

If pollen is transferred from the anther to a stigma on the same flower, you have self-pollination. This process is known as autogamy. For autogamy to occur, both the stamen and pistil must be fertile at the same time.

Additionally pollen may be transferred from the stamen of one flower to the pistil of another flower on the same plant, a process known as geitonogamy.

Self-pollination can occur due to wind or bee or insect visiting the bloom. And should a flower not be pollinated in these preceding ways, it can sometimes self-pollinate after wilting where the petals collapse onto itself, and force the anthers into it’s own stigma.

Cross Pollination

A flower is cross-pollinated when pollen from the stigma of a flower from one plant reaches the pistils of a flower on a different plant. Like with self-pollination, cross-pollination will occur primarily due to the wind or insects.

Cross pollination is sometimes desirable to create new varieties of fruits and vegetables, or cultivars of plants. Think of all the different species of tomato that have been created over the years, or different breeds of apple. This all occur due to cross-pollination.

Flower anatomy

In general, the key organs or parts of a flower are present on most species. Although there are certain flowers that only have male or female flowers, or even only male or female on the whole plant (like Spicebush).

The image at right is reproduced from the Image reproduced from Wildflowers of New York, H. D. House, 1918. [2] This is what is known as a ‘perfect’ flower containing all components. [2]

(A) petals, all of them forming the corolla;

(B) sepals, all of them forming the calyx;

(C) the stamen, composed of (C) the filament, and (C1) the anther, which produces the pollen;

(D) the pistil, consisting of the large and somewhat swollen base (ovary), a more slender shank (style), and the larger or branched tip (stigma).

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The image at right shows the cross-section of a botanically perfect flower. A flower that is ‘botanically’ perfect contains a stamen (anthers and filament, the male organs), a pistil (stigmas, style, and ovary) the female organs.

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An example of the Labiatae family. Note the two-lipped floral structure with several stamens. The plants pictured are commonly known as Bee Balm, Mountain Mint, and Self-Heal. [2]

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For some floral examples of legumes, we can see Blue False Indigo, Showy Tick Trefoil, and Partridge Pea. Note that each of the flowers have a similar florm, and all of these plants will produce seed-pods, just like green beans or peas. [2]

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Diagram of the flower from the Asteraceae Family. Frequently members of this family will have both disc and ray flowers such as in Rudbeckia or Echinacea. You can save seed by both pulling the petals of Echinacea, or dislodging the seed from the disc flowers through vibration. [3]

By far one of the most expansive families of flowers, the Asteraceae has hundreds of species.

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Some more examples of the Asteracea family. Ironweed, Asters, Sunflowers, and even dandelions are all within this family. It is quite a large and diverse grouping.

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How flowers are arranged on a plant

When you encounter a flower in bloom, it is often not a single flower, but many. As you gain experience you will start to recognize these floral structures naturally. But, they are important to note.

The diagrams below show different arrangements of inflorescence. Each circle represents an individual flower. Study this image, and think now to flowers you grow in your yard or see out in nature. They all correspond to one of these arrangements.

Sources [1] [3] [4] [5]

Examples of flowering spike plants would include Liatris Spicata and White Turtlehead.

Chelone glabra turtlehead bloom
A flower spike of White Turtlehead

Some examples of raceme flowering plants plants would include many members of the Lobelia genus such as Cardinal Flower and Great Blue Lobelia.

Panicle flowering plants would include the Cup Plant and Smooth Blue Aster.

Examples of simple umbel flowers include Yellow Wood Sorrel and Butterfly Weed (Asclepias tuberosa).

Asclepias Tuberosa Butterfly Weed

Queen Anne’s Lace and would be and example of a compound umbel inflorescence.

And finally, Ironweed would be a good example of a corymb inflorescence.

A corymb of Ironweed flowers

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[1] – Taylor, Norman, The Science of Plant Life. P.F. Collier & Son Company. 1922.

[2] – House, H. D., Wildflowers of New York. Albany, University of the State of New York, 1918.

[3] – Duncan, Wilbur H., and Marion B. Duncan. Wildflowers of the eastern United States. Vol. 20. University of Georgia Press, 2005.

[4] – Wilhelm & Rericha; Illustrated Glossary of Botanical Terms. Flora of the Chicago Region. Indiana Academy of Science (IAS). 20SEP2020. Accessed 22JAN2022.

[5] – Lindley, John. The Elements of Botany, Structural, Physiological, & Medical: Being a 6th Ed. of the Outline of the First Principles of Botany, with a Sketch of the Artificial Methods of Classification, and a Glossary of Technical Terms. Bradbury & Evans, 1849.