The tightly-packed black mystery seeds from last week belong to the plant commonly known as pyracantha or sometimes firethorn.
The fruit are bright red, making it a lovely plant this time of year.
Several species in the genus Pyracantha are grown as landscape plants throughout the world, but Pyracantha fortuneana is the most common species in the desert Southwest. It was originally from China.
The berries are edible, but not sweet. They can be used to make jelly, for example using this recipe.
Birds, such as the Northern mockingbird, eat the fruit as well.
Do pyracantha grow where you live?