Our mystery fruit/seeds from last week were from a yellow oleander, Thevetia peruviana.
Yellow oleander is named for its bright yellow flowers (although some varieties have light orange flowers).
Yellow oleander is originally from tropical regions of Central and South America, but now is grown throughout the world. Being tropical, it is quite frost sensitive. Here in the Sonoran Desert it is often used in landscapes next to houses or walls, which radiate heat. It is grown as a tall shrub or small tree.
The trees are evergreen and flower over an extended period.
The down side to these plant is that yellow oleanders are toxic. All parts are poisonous if eaten, and the sap can irritate the skin in sensitive people.
Even the seeds within these oddly-shaped seed capsules are poisonous.
The seed capsules are hard and have a raised area or ridge that is often apparent even when they are fresh and green.
Do yellow oleander grow where you live?