Category Archives: Iris

Iris hexagona (or I. savannarum)

(Iris is Greek for rainbow.  Hexagona counts the angles on the seedpod.  Savannarum is where it lives.)

Iridaceae, The Iris Family

The geographical consequences of evolution do not always fit our tidy 18th Century classification categories,  iris for instance    My two favorite go-to references disagree on the species identify for the wild blue-violet iris around town.  No surprise.  Irises defy easy species classification:   they hybridize, they spread as clonal populations each with its own character,  they vary geographically.   You get the picture.  Messy.  Naming iris species is like naming clouds merging and separating across the sky.  A rich, dynamic tapestry of ever-evolving variation overmatches a classification system based on sorting dead pressed museum specimens..

Call it what you will, sometimes you just have to put a plant in the blog for its celebrity good looks.  What flower is prettier than these?  John and I stumbled upon a natural iris garden blossoming by a muddy pond near Jensen Beach, Florida.

Iris hexagona 5

The big showy droopers with yellow marks are the sepals.  Lying tightly on top of them with tips elevated are the styles.  The petals are upright between the sepals.   Photos by John Bradford.

Standby for pollination complexity. Those big showy drooping “falls” with the beckoning yellow nectar guides are the sepals, which in most other flowers are green no-count lobes upstaged by colorful petals.  The iris petals are less showy and less involved than the sepals, a case of role reversal.    Lying intimately atop the colorful sepals are the styles, likewise fancy and out of character.  In most flowers the styles are nondescript green stalks connecting the pollen-receptive stigma to the seed-making ovary. Ho hum.

Iris hexagona 1

But the iris style is a horse of a different color.   It is as colorful as the sepals, lying intimately atop them. The visiting bumblebee, the predominant pollinator in our species, pushes into the blossom squeezing between the sepal and style covering it.     The pollen-snatching stigma lies within a  hinged flap on the underside of the style, scraping pollen off of the inbound bee’s back.   Then deeper in the blue tunnel new pollen dabs onto the bee seeking its nectar reward.   As the bee backs out upon completing its mission, it pushes the stigma-covering flap closed, preventing self-pollination

Someday somebody’s going to study the hormonal life of rhizomatous clonal plants sprawling as single genetic individuals covering acres.  A single big plant with the leaves and flowers scattered across a broad network of rhizomes has a problem—how does a plant stretching all the way across a marsh communicate from one side to the other?   They do not have nerves or circulating blood.

Iris hexagona 4

The best way for the point of attack to communicate impending trouble perhaps is across the air.   Iris hexagona has attracted research attention in this connection, most prominently by biologist Susan Mopper in Louisiana.    Iris hexagona uses a hormone called jasmonic acid in conveying a danger signal probably over long distance, given that jasmonic acid volatilizes for airborne delivery.  This is extra interesting because jasmonic acid has not been a known plant hormone for very long.  And yes, it is named for jasmines where it was discovered.   Dr. Mopper and collaborators showed that saltwater stress prompted Iris hexagona to bolster its defenses against leaf-damaging insects, in other words, one “attack” spreading the alarm girding the plant for the next battle.

To linger a moment on jasmonic acid,  it seems more or less to form from damaged membranes, pretty ingenious, a warning based directly on the immediate debris of damage, sort of like pulling the fire alarm upon smelling smoke.

Ipomoea indica Baker Rd.

Morning Glory hanging around the iris, the same color.


Posted by on April 7, 2017 in Iris, Uncategorized

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