Ecuador, along with the rest of South and Central America apparently, has perfect weather conditions for growing fruit, particularly along the coast and in the Amazon basin. Thus for a gringo such as myself, attempting to purchase fruit or juice can be rather intimidating, because not only do I usually lack the word, but I can't even recognize by sight things other than bananas and strawberries. However, I have learned enough to offer a short discourse on the subject and make recommendations for my fellow travelers.
Most days my breakfast consists of pieces of papaya and banana or mango. These easily recognizable ones are served with a fruit juice and homemade jam, both of which consist of blended fruit, water and sugar. The only main differences are that the jam simmers for a few hours in a pan and has less water. Along with this my house mom always eats pitajaya, which is a yellow fruit roughly the size and shape of a pineapple grenade that is clear with black seeds on the inside. It tastes quite good, but it's main purpose is to keep the intestines chugging—or float the stomach, as she says.
Tomate de arbol (yes, tree tomato) is also delicious, and almost always served as a juice. Its appearance is quite similar to a roma tomato on drugs, which is to say about three times larger. It's one of the more common juices offered in restaurants, and seems to go quite well with a bagel and cream cheese (and the local gringo market).
Maracuya is another popular fruit for juice. To be entirely honest I don't know what it looks like, having just discovered that it is quite refreshing. Based on Ecuadorian Juice Theory I would guess that it is somewhat bitter with a strong flavor as a juice. I devised Ecuadorian Juice Theory after we had a school-sponsored fruit tasting session with about 20 different samples. It was amazing how many of them were horrible to eat—but as our teachers told us, the horrible ones are almost always great as juice. The reason, of course, is that any quantity of sugar added to a drink is quite acceptable in Ecuador.
By far my favorite fruit is guanabana, which I became acquainted with in Mexico. I made the mistake of buying one to make juice a few weeks, and paid the price with an hour of picking out the slippery black seeds from the white, stringy fruit that is somewhat larger than a pineapple. The result of my labor, however, was the best-tasting juice available in Ecuador, as apprized by myself and the neighbor girl that is eight years old.