Those lovely purple-leafed plum trees (Prunus cerasifera) that dot city streets and suburban communities, as long as they are not a non-fruiting cultivar, can produce a large crop of small purple fruits. Most of the time, however, these end up as a nuisance on the ground and nobody consumes them.
For those curious, however, the wealth of plums can be put to a purpose other than being a stain on the sidewalk. Because nobody eats them, ornamental plum fruit are often regarded as not being edible. This is supported if you just pop one into your mouth, because when eaten out of hand most ornamental plum fruit are very sour, though you will run into the occasional sweet one. They are very edible, however, and can be delicious if used properly.
The anti-oxidant juice from these plums is very tart, not very sweet, and has a nice floral fragrance. I run these plums whole through a food mill and produce a plum puree that is excellent on pancakes, ice cream, and in yogurt. It is even very useful as a part of a marinade for meats, especially in combination with barbecue sauce.
If you have a flowering plum tree that drops huge numbers of purple fruit each year, try making plum sauce. Not only will it put an unused food source to use, but it can open a new and interesting dimension to your diet.