Floral symmetries

Floral Symmetries

The flowers of roses, magnolias, buttercups, and water lilies are radially symmetric. That means that the petals are identical in design, and project from a central point or focus.

The flowers of orchids, peas, and most gesneriads are bilaterally symmetric. That means that for every part on the left-hand side of the flower, there is a matching part on the right-hand side (and vice versa). "Bilateral" means two-sided. A bilaterally symmetric flower has two sides (left and right) which are mirror images of one another.


Here is an example of each for a flower with five petals.


      Radial Symmetry             Bilateral Symmetry

            P                          Q   :   Q
                                           :
       P         P                         : 
            *                         R    :    R
                                           :
         P     P                           :
                                           S


In the left diagram, the P petals are all the same, "radiating"
from the central point (marked with an asterisk).  In the right
diagram, the two Q petals are mirror images of one another, as
are the two R petals.  The S petal it its own mirror image,
since it lies on the line of reflection (the row of dots).  In
a resupinate (see Glossary for definition) flower, the diagram
would be flipped vertically, with the S petal at the top.

The picture of Sinningia gertiana shows a bilaterally symmetric corolla whose main deviation from radial symmetry is in the bend of the corolla tube.

The picture of Vanhouttea lanata shows a flower which is definitely not radially symmetric.

The sinningia flowers which are the furthest from radial symmetry are those with a galea, in which the two upper petals (corolla lobes) are extended and fused into a kind of hood.

Regardless of how similar the petals look, there are two elements of sinningia flowers which are never radially symmetric. There are always four stamens, which are bilaterally symmetric. The fruit has a single chamber and splits into left and right halves (bilateral symmetry) when ripe.

Peloria

One sinningia species, Sinningia speciosa, does have radially symmetric flowers. These are the well-known "florist gloxinias". This condition is known as peloria, and such flowers are called peloric.

Many species which do not normally have radially symmetric flowers can have the occasional peloric flower. Normally, this is due to a non-hereditary quirk in the development of the flower concerned. Sometimes, however, the peloria is the result of a mutation, and is inheritable, as is the case for florist gloxinias.

Another species, Sinningia cardinalis, has a variety, called 'George Kalmbacher', with hereditary peloria.