The Beauty and Function of the Iris Flower

The beauty of the iris bloom is captivating; and we are all desirous of owning the latest hybridized beauty.  Seldom do we consider nature’s design in the function of these beautiful flowers.  Flowers are specialized in shape and are designed to ensure that pollen grains are transferred to pollinators in their search for the nectar attractant. The genus Iris belongs to Iridaceae, a large family with some 200 flowering plant species with flowers consisting of parts in sets of three.  The three-part iris flowers can form either singly or severally on branches of the flower stalks.  Each iris flower is made up of six segments, three upright standards and three downward falls. The standards serve as colorful banners to attract pollinators, and the falls serve as landing pads for pollinating insects.   One or more iris buds are enveloped within two modified leaves called spathes.  The spathes may be papery or thicker in structure.  The standards and falls make up what is called the perianth. The six petals grow from a perianth tube, the bottom of which consists of the flower’s ovary. 

The Male Organs of the Iris Flower

  • ·Stamens are the pollen-bearing male organs of the iris flower.
  • ·Anthers bear the pollen grains and are located at the top of the stamens.  The anthers excrete nectar at their base.
  • ·Filaments are the stems of the stamens. 

The stamens are located under the style and facing the claw of the branches.  Three style branches also grow from the perianth tube.  These style branches arch over the anthers. 

The Female Organs of the Iris Flower 

  • ·Perianth Tube surrounds the pistils and connects the ovaries with the perianth.
  • ·Pistils are the female organs of the iris flower consisting of stigma, style, and ovary.
  • ·Stigma is the sticky top of pistil serving as receptive surface for pollen grains
  • ·Style is the stalk of the pistil, between the stigma and the ovary, through which the pollen tube grows.  The style connects the ovary with the style, which is positioned opposite the falls.
  • ·Style Arms are the small stiff portions of the bloom extending over the beard.

 ·Style Crests are two little “wings” or fringe on the ends of the style arms that shelter the stigma.  Gently lifting the end of the style crest causes separation to reveal the receptive stigmatic lips.  Located underneath this is the anther.  The stigma is the ridge or lip located at the top of the undersurface of the style arm, and it is here that pollen grains must be deposited to begin the pollination process.

  • ·Ovary is the enlarged base of the pistil containing the ovule.
  • ·Ovule become seeds upon fertilization.
  • ·Hafts are located at the base of the falls and standards where they begin narrow near the center where they connect to the stem of the flower. 

Located near the extremity on the underside of the style branch is the stigmatic surface through which the iris flower is fertilized.  A tunnel is formed with the style arms representing the roof of the tunnel and the hafts of the falls representing the floor of the tunnel.  The stigma has a downward trajectory, and at the mouth of the tunnel, located along the roof are the anthers.  On bearded species, there is a line of colored hairs located on the central line of the falls at the very heart of the flower.  These colored hairs are called the beard which either matches the flower color or can be a contrasting shade. These are nectar guides which direct pollinators toward the nectar source.  A patch of contrasting color surrounding the beard, often white or yellow, is called the signal.

The form, color, and aroma of the iris flower combine to attract pollinators to the iris flower.  The beard, signal, and structure of the falls both attract pollinators and provide a landing platform for them.  When insects or hummingbirds reach into the nectar bearing tube of the flower’s stamens, they pick up pollen grains when brushing by the pollen-bearing anther.  When visiting another flower for nectar, the pollinator brushes by the wet stigma and transfers pollen grains.

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