- Floral symmetry
Floral symmetry refers to whether, and how, a
flower can be divided into two or more identical or mirror-image parts.Most flowers are actinomorphic ("star shaped"), meaning they can be divided into symmetrical halves by more than one longitudinal plane passing through the axis, much as a pie can be cut into several equal and identical pieces. In these flowers, the
petal s are usually similar in shape, size, and color. Such flowers are also called radially symmetrical or regular flowers. Examples of actinomorphic flowers are thelily ("Lilium ",Liliaceae ) and thebuttercup ("Ranunculus ",Ranunculaceae ).Zygomorphic ("yoke shaped") flowers can be divided by only a single plane into two mirror-image halves, much like a
yoke or a person's face. Examples areorchid s and the flowers of most members of theLamiales (e.g.,Scrophulariaceae andGesneriaceae ). Zygomorphic flowers generally have petals of two more different shapes, sizes, and colors. Least commonly, flowers may be asymmetrical; they cannot be divided into two identical or mirror-image halves on any plane. Such flowers are typical of most members of theZingiberales , such as cannas and variousginger s. In most cases, different kinds of floral symmetry are linked to particular pollinators.Actinomorphic flowers are a basal angiosperm character; zygomorphic flowers are a derived character that has evolved many times.Losos, J. B., Mason, K. A, & Singer, S. R. "Biology, 8th. ed." New York, NY: McGraw Hill.]
Some familiar and seemingly actinomorphic flowers, such as those of
daisies anddandelions (Asteraceae ), are actually clusters of tiny zygomorphic flowers arranged into a radially symmetricinflorescence .Peloria or a peloric flower refers to an aberration in which a plant that normally produces zygomorphic flowers produces actinomorphic flowers instead. This aberration can be developmental, or it can have a genetic basis: the
CYCLOIDEA gene controls floral symmetry. Peloric "Antirrhinum " plants have been produced by knocking out this gene. Many modern cultivars of "Sinningia speciosa " ("gloxinia") have been bred to have peloric flowers as they are larger and showier than the normally zygomorphic flowers of this species.References
* P.K. Endress. 2001. Evolution of floral symmetry. "Current Opinions in Plant Biology" 4: 86-91 (abstract [http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=11163173&dopt=Citation here] )
* P.R. Neal, A. Dafni and M. Giurfa. 1998. Floral symmetry and its role in plant-pollinator systems: terminology, distribution, and hypotheses. "Annual Review of Ecology and Systematics" 29: 345-373 (abstract [http://www.jstor.org/view/00664162/ap010001/01a00130/0 here] ).
Wikimedia Foundation. 2010.
