Plants that go through photosynthesis use carbon dioxide to create their own nutrients. Most of these plants are green in color, because the green color comes from chlorophyll molecules that are a necessary part of the process of photosynthesis. Some plants do not create their own nutrients, but instead get them from other sources. These plants are not usually green in color.
Orobanche is the name of a group of holoparasitic plants. Holoparasitic plants are plants that are attached to a host plant. They get their nutrients directly from the host plant, which makes them a parasite. They do not use carbon dioxide and do not photosynthesize, which means they have no green parts, nor do they release oxygen. Often called broomrape, Orobanche numbers over 200 species. The seeds of broomrape lie dormant in the soil, sending out roots until they find the roots of a host plant to attach to. Once that happens, they flower. The flower is between 10 and 60 centimeters tall, and has pale blue flowers similar to a snapdragon. The broomrape and the host plant are only attached at the roots, so when the Orobanche is not flowering, no part of it can be seen above the soil.
Hydnoraceae is also the name of a group of holoparasitic plants. The group is composed of seven species that are native to Central and South America, Africa, Madagascar and Saudi Arabia. The flowers of the plant are highly unusual in that they do not contain any leaves. They can present above ground, or remain entirely underground. Like Orobanche, Hydnoraceae attach to the roots of the host plant.
A myco-heterophyte is a type of plant that is also connected to a host plant--usually a tree. Instead of drawing nutrients directly from the tree as holoparasitic plants do, myco-heterophytes are connected to the tree via a fungus. The fungus transfers the nutrients from the tree to the plant, in effect "feeding" it. Examples of myco-heterophytes include the bird's nest orchid and Indian pipe. Both holoparasitic and myco-heterophyte plants produce seeds and flowers, but because they do not go through the process of photosynthesis, there is conflict among scientists whether to even call these parasites plants.