The hybridation is possible from all the orchids of the same specie?

[alessandro2011]

Or only between some variety of the same species?

[RobS]

Orchids are special for that they have very weak crossing barriers between species (probalby one of the reasons for the huge diversity). I don't know of any family / genus of orchids where hybrids are not possible within the family / genus. But I can imagine there are some. An extreme example is the cattleya alliance where very complex hybrids between different genera are possible and fertile.

[alessandro2011]

Interesting.
Cattleya Alliance Species and Hybrids
From now on i would like put more attention at the note about the parents of Hybrids.

Where i can find information about hybridation?
For example here said that the Brassavola nodosa transmits it to his descendants:

the compact size of the plant
the size of the flowers
the ability to bloom several times a year
the long-term flowers
the curious aspect of the leaves
and also the smell at night.