Our mystery seeds from last week were from the natal plum, Carissa macrocarpa.
(Photograph of natal plum flower and fruit by Forest Starr and Kim Starr Creative Commons Attribution 3.0 Unported license).
As you can see, the fruit of the natal plum resembles a plum, hence the common name.
The seeds inside, however, do not resemble a "plum pit." They are flat and occur in a cluster.
Natal plum is a perennial shrub native to South Africa. It is currently grown in warm regions throughout the world. It is quite frost sensitive, dying back in cold winters even here in the low desert.
The healthy leaves are a deep green, which contrast with nicely the large white flowers.
Some people do eat the natal plum fruit, especially cooked with sugar in the form of jams and jellies. The plant and fruit contains a milky sap that oozes out of breaks in the skin and can look unappetizing.
Do natal plums grow where you live?