Rose flower diameter

According to the UPOV guidelines, the diameter is measured on a fully opened flower whose petals are carefully flattened horizontally for data accuracy. The value is recorded in centimeters and serves as a baseline parameter when creating a variety passport, with specific values varying significantly depending on the varietal group: from small in border and polyantha roses to large ones, reaching 15–16 cm, in hybrid teas.

In agronomy and breeding, this trait serves as a critical marker of commercial quality for cut flower varieties and a tool for classification. Since flower size can vary under the influence of agricultural practices, growing conditions, and plant age, it is always evaluated in conjunction with other characteristics, such as bud shape and growth type.