That's an easy one...Maclura pomifera (aka Osage-orange).

Best advice to you without actually seeing the edge concerned about, is, check with a local millwork shop. They can make you a wood trim that will be durable and pleasant to the eye. If you have a good carpenter handy, any type of finish edge can be made with some craftmanship and time. Tip, you can soak wood in water to get it to bend if that is needed, hope you find what you need.

Lots of things to consider. Where are you located? What state? Location has a lot to do with what you should and/or could plant. Stone fruit is usually advised to plant in full sun with good air circulation. Many even prune their trees open centered or vase shape to let more sun in and air flows better. Thus, growing stone fruit as a hedge may not be a good idea. Also, you need to think long-term, those tiny sticks can grow tall, far and wide. Planting only 1 ft from a fence will force you to consider a certain way of pruning it. A plum can put out 3-4 ft branches in all directions in a growing season. Let's start with what state do you live in?

Yes I've heard of tamarinds being used in salad dressing and also savory Indian and Mexican dishes.It could be tamarind,but OP E C hasn't chimed in to provide any more background info.I had tamarind candy that had Chile pepper in it that was a little strange at 1st taste,but became addictive.The size of pit next to nickel would fit with tamarind.