Longan is a sweet fruit about the size of a grape, with a tough outer shell surrounding a translucent core with a large seed inside. It grows on small trees in warm moist climates.
The people of the Mekong Delta have always grown rice as their staple crop, but in recent years the trend is toward longan because it's possible to make much more money per acre or hectare, and it's less work than growing rice.
Rambutan (right) is another popular sticky-sweet fruit in Vietnam.