In hazelnut seedlings “Istrian long” the fruit shell is dark brown, with darker stripes. The top of the fruit is covered with gray hairs, which sometimes reach its middle. The seam is poorly expressed. Its thickness is 1,430 mm.
The epidermis of the nucleus is dark brown and smooth. The pellicle is thin and easily separated from the smooth core.
The core of the Istrian rainbow variety contains: 64.38% crude fat, 16.62% protein and 3.34% invert sugar.
The leaf is large, irregularly rounded, without a pronounced spike.