Our wrinkly mystery "nuts" in the wrinkly fruit last week were from jujube or Chinese date, Ziziphus zizyphus (older: Ziziphus jujuba).
Jujube have interesting fruit.
At first the fruit look (and smell) like a oval apple.
Over time the fruit become reddish brown and wrinkly, as you can see towards the top in this photograph.
Once dried, they look like dates.
Inside the fruit is a "nut" or "pit" rather like from an olive. It turns out that I mislead you last week because this is not really the seed.
(Illustration by L.H. @ USDA-NRCS PLANTS Database)
As you can see from this drawing, inside the "nut" are two seeds lying side by side. It would require a sharp knife and patience to get them out.
The tree looks somewhat like a spindly pear tree and has similar growth habits. It is deciduous in the winter and requires a brief chill to properly set fruit. Although originally from Asia, they do grow in the low deserts of Arizona.
Have you ever seen a jujube? Did you try the fruit? What did you think of it?