It is considered to be an Italian herb, but since it was popularized in America in the late 1940s, oregano, Origanum vulgare, has become more popular in Italian-American cuisine than it is in Italy. It is now the traditional ‘pizza herb’ for American style pizza. Oregano happens to be one of the few herbs that is preferred dried rather than fresh. Only foliage is used, either before or after bloom.
Prior to bloom, foliage is low to the ground, on wiry stems. Blooming stems stand vertically as tall as two feet, with more foliage and tiny purplish flowers that are not very flashy. The flavor of the foliage on the upright blooming stems is distinct from that of the prostrate vegetative stems. The opposite leaves are only about an inch long, or slightly longer. Flavor can be variable with weather.
Flavor is also variable by cultivar. Some are spicier than most. Some are more bitter. Some cultivars were marketed to be more visually appealing in the garden than flavorful in the kitchen. ‘Nana’ is a dwarf. ‘Aureum’ is variegated with yellow. The famously flavored ‘Greek Kaliteri’ has compact growth, with atypically thick and slightly fuzzy leaves that are dark on top and purplish underneath.