Peloria is an unusual regularity in the form of a flower that is usually irregular. A flower that is usually asymmetric (say with three petals) is peloric when it “doubles” the number of petals to six and then appears symmetric in shape.
In 1744 Carl Linnaeus observed this phenomenon in toadflax and first used the term peloria to describe the condition. Peloria comes from the Greek and means “monster”. Since then peloria has been observed in many species and has generated much research to determine its cause.
Peloria can be genetic or developmental in origin. Several plants, some orchids and gloxinia for example, are specifically bred to exhibit this trait. The CYC gene controls floral symmetry and removing this gene artificially induces peloria. When all flowers in an inflorescence or plant that is normally irregular are symmetric the cause is usually genetic.
If scattered flowers or only the terminal flower exhibit pelorism, environmental factors are more likely to be causative. Nutrient deficiency, insect pests, lack of water, temperature extremes and radiation during floral formation are some of the possible stressors inducing peloria.
Northern water plantain (Alisma triviale) flowers normally have three petals and three sepals.
While photographing northern water plantain flowers between the North and South Elkins Barns at Ash Creek Wildlife Area (Modoc County CA) in July, I noted a single unusual flower. Instead of being asymmetric, this flower had six petals and sepals and was symmetric – a peloric flower.
Another term used instead of peloria is epanody.
A previous post, Northern Water Plantain 08-17-21, provides more information about this wildflower.