From the plant I am looking for I know only the fruits (see the middle of the picture). The fruits are smaller and a little bit slimmer than apples. The end where the flower has been is round (like a tomato). The fruit inside has a consistence like a firm pear. The flavor is fresh and sweet like an apple or a pear. In the middle there is no stone but a kind of small carpel which I unfortunately did not examine further.
As I was told by a Thai woman the name should be "phut saa". When looking up this name in Google I found only the translation "jujube" (Ziziphus spec.). Both species of that genus I know of (Chinese Jujube, Z. jujuba, and Indian Jujube, Z. mauritiana) have fruits which are very different from the fruits I have photographed and eaten.
The fruits have been sold in november in many places in the north-east part of Thailand. Can anybody help me?
Compare your picture with that in the Khmer Online Dictionary -- the fruit looks similar and the Cambodians are identifying it as Z. mauritania. (Scroll down and click on the jujube listing -- I can't link to it directly from Dave's Garden).
I grew them here in Texas for a bit but they are not very cold hardy.
You can grow the Chinese Jujube in your area. Sugarcane Jujube would be a good purchase for you. It is smaller in size but very sweet.
I knoe Echo community carries them seeds... they are at south Florida... think it's $6 for a packet or so... they did germinate when I bought them last year. But there is 1 type that don't have thorns... not the 1 at Echo