The crested flower form is subdivided into double and single crested. The crest or central disc petals are the dominant feature in either flower form.
The center contains numerous short petals tightly clustered. Surrounding this crest are the ray petals, broader and flatter. If there is only one row of ray petals surrounding the crest it is considered a single crested flower form. If there are three or four rows of ray petals, it is a double crested French marigold. There have been many recent introductions in the double crested form. At this time there are no hybrid French marigolds.
In the garden, the T. patula marigolds are considered dwarf French. They range in height from 6 to 14 inches when mature. A gardener can choose from 1 inch to 2-1/2 inches for flower size. This species is the most popular of all marigolds. Easy to grow under most weather and soil types, French marigolds are reliable annuals.
Source: National Garden Bureau