If you read ingredients on processed foods, you will see mono- and diglycerides listed frequently. Fats are triglycerides - there are three chains of fatty acids trailing off the glycerol head of the molecule. Mono- and diglycerides act as emulsifiers because they can bond to both water and oil, and I believe they may also be used as dough conditioners. Lecithin is the best known diglyceride; it makes up a large part of egg yolks and is famous for its ability to emulsify. My question is, what are other naturally occurring mono- and diglycerides, and do they have any use for the home cook?
Lecithin is a mixture of stuff, which also involves mono and diglycerids. As far as I recall, there is no product naturally produced in nature which is pure mono or diglycerid. Fats in nature follow a lot of synthetic paths, not only for energy storage, but also for structural needs (the cell membrane, for example). For this reason, you are very unlikely to find a biological system synthesizing only one molecular species, and I would be surprised it actually exists.
As for what kind of mono and di, it's hard to say. The metabolic pathways synthesize oleic, palmitic, stearic, arachidonic, butirric chains, among others. The broad set of different combinations, and their proportions lead to oil, or butter, or whatever else. In addition, some residues are phosphated, or they are used to create Sphingolipids. The proportions are decided by the plant/animal metabolism and general conditions.