Orchids are herbs (having no woody tissue) and are placed in a major subclass of the plant kingdom known as the monocotyledons. Other plants in this subclass include grasses, lilies, gingers, and palms. All plants of this type have some features in common, in particular sheathing leaf bases, parallel venation, and a single seed leaf. All orchids have three petals and three sepals which may be alike or dissimilar, however, the third sepal is nearly always greatly modified and very different in size, shape, structure and often color from the others. This is known as the labellum or lip, and it plays a major role in the pollination of orchid flowers. Another significant development of orchids is the combination of the male and female sexual parts into a central structure known as the column. The anther and stigma are separate on the column, although both organs are often situated close together. Orchid seeds are also highly interesting, being minute and dust-like. A single capsule may contain anywhere from 1,000 to nearly 4,000,000 seeds, depending on the size of the fruit and the species. Individual orchids are judged according to a number of factors, including the flower's color, the number of blossoms per spray, the size of the flowers, and their presentation on the spray. Additionally, flowers should show no spotting, no reflexing of sepals or petals, and have an overall round and pleasing shape.