Flip-Flopper Flowers

07 Mar

Spurred Butterfly Pea

Centrosema  virginianum


Centrosema virginianum 7

John and George devoted much of the day to revising our Grass and Sedge web site (you will still see the “bad” old version), but today was too enticing to remain cooped up inside, so we took a botanical look at the Hawk’s Bluff Trail, a scrubby coastal dune area near Jensen Beach, and part of Savannas Preserve State Park.  Any witness would testify that the flower show today was Butterfly Pea, Centrosema virginianum.  Hundreds in bloom decorated the trail.

These are curious members of the Pea Family, with an odd twist.  To establish comparative context, let’s start with normal pea-type flowers.  There are  five petals (see the diagram, top yellow images).

  • A “banner,”  which is a showy billboard rising up above the rest of the flower
  • Two “wings” which stick out straight from the center of the flower.   These paired petals can be small or sometimes tough to see.  They are not important today.
  • And a “keel” at the base of the flower made of two petals joined to form a boat-shaped envelope, open-side-up serving as landing platform for bees.  The keel contains the business parts of the flower, the pollen-receptive stigma and the pollen-making anthers.   When a bee lights on the keel, the keel bends down, and the stigma and anthers pop up to contact the underside of the visitor.   This sort of normal pea flower is detailed in an earlier blog

Now, turn the beat around.  In Centrosema (and in similar Clitoria) the flower is essentially the same but flipped, with the keel on top and the banner at the base, the banner now serving as landing platform. When an insect visits these flowers, the keel with its stigma and anthers is above the bee.

Top: Standard pea-type flower Bottom: Flipped Centrosema flower

Top: Standard pea-type flower
Bottom: Flipped Centrosema flower

Side view, with X-ray vision, of Centrosema keel and the style hidden within

Side view, with X-ray vision, of Centrosema keel and the style hidden within

A similar flip-flop is seen in Orchids.  In a minority of Orchids the big showy petal (called the labellum) rises up just like the banner in normal Pea Flowers.  And the stigma/anther unit (called the column) serves as landing platform just as the keel hiding the stigma and anthers does in a standard Pea Flower.  (Such Orchids are called non-resupinate Orchids.)

The majority of Orchids, however, are flipped 180 to resemble Centrosema, that is, with the labellum (banner) as the welcome mat, and the stigma-anther unit arching above.   (Such Orchids are called resupinate Orchids.)  Here are some resupinate Orchids.   CLICK

You can see the odd resemblance of resupinate Orchids to Butterfly Peas.  And so can so-called “Orchid Bees,” that is, Euglossine Bees, caught in the act occasionally of visiting Centrosema.  BUZZ here  Is the Centrosema floral-flip a mechanism to poach Orchid bees*?

Those flowers are flip-floppers!

Those flowers are flip-floppers!



*Don’t let me over-state the “Orchid Bee” -Centrosema hunch, which has occurred to other botanists before today.  Euglossine bees are not limited to Orchids (and to Orchid lookalikes), and Centrosemas do have a variety of floral visitors.  But still, Orchido-centric bees visiting Orchid-mimicking flowers is fertile hunch fodder.

John and I enjoyed the common Centrosema virginianum,  but there are additional Butterfly Peas in Florida. Centrosema arenicola is state-listed as endangered; most of its range is Central Florida.  Another, presumed to be a garden escape, is Centrosema sagittatum.  (There are similar species of Clitoria also.)

Being good legumes, Centrosemas serve as cover crops,  green manures, and rubber, and as livestock fodder.


Posted by on March 7, 2014 in Butterfly Pea


Tags: ,

3 responses to “Flip-Flopper Flowers

  1. kim

    November 27, 2016 at 8:46 pm

    so where can we get some C. arenicola seeds to help the poor little beans out. I live in orange county, fl. so there ought to be some nearby somewhere.

    • George Rogers

      November 27, 2016 at 9:01 pm

      I don’t know. For any native species to check commercial availability I go first to

      • kim

        November 28, 2016 at 8:38 am

        Thanks for the tip George.


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