P&PDL Picture of the Week for
June 1, 2009

Single Versus Double

B. Rosie Lerner, Extension Consumer Horticulture Specialist, Department of Horticulture & Landscape Architecture, Purdue University

Why are some flowers referred to as "single", and others as "double", and still others as "semi-double"?

The answer lies in the petal count. A single flower has a single count of petals, such a this single rose bloom. Different species of plants vary what is considered a single number of petals. Five is the most common single flower petal count among the various horticultural species, but some species have 3, others have 4.

A double flower has some multiple of single petal count. Semi-double would be a multiple number between single and double count.

How these terms are exactly defined may vary depending on the species. The American Rose Society has established the following definitions for petal count on roses.

SINGLE - 4 to 8 petals
SEMI-DOUBLE - 9 to 16 petals
DOUBLE - 17 to 25 petals
FULL - 26 to 40 petals
VERY FULL - more than 40 petals

The terms 'fully double' and 'very double' are often seen in publications but are not official, nor have petal counts been assigned to these terms.

Click image to enlarge

Single

Single

Double

Double

Semi Double

Semi Double

Full

Full

Very Full

Very Full

Purdue Plant & Pest Diagnostic Lab Purdue Cooperative Extension Service