A distinction between monandrous and other flowers is particularly relevant in the classification of orchids. A few hypotheses have been proposed to explain worker policing in the monandrous "P. chinensis". A distinction between monandrous flowers and others is especially important in the classification of orchids. The female then selectively chooses her mate and begins a monandrous relationship. "M. rotundata" has been found to be a monandrous bee species. A monandrous flower is one that has only a single stamen. Like many others before him, Dressler believed that the monandrous orchids form a monophyletic group. After mating the female is unreceptive to other males and remains monandrous. The flowers are monandrous in the subfamilies Vanilloideae, Orchidoideae, and Epidendroideae. The monandrous female must choose which type of male can help her reproduce successfully. In animals, a monandrous system occurs when females have one mate at a time. The monandrous orchids form a clade consisting of the subfamilies Orchidoideae, Vanilloideae, and Epidendroideae. In botanical terms, monandrous simply means to have a single stamen. "D. subobscura" is monandrous, a behavior not usually seen among "Drosophila". However, many other species of bees, including bumblebees, such as "Bombus terrestris", are monandrous.