Horned/Barbed/Spined has nothing to do with it - meditation has to do with the leather armor TYPE.
Bone - Non-med
Studded - Non-med
Leather - Medable
Leaf - Medable
Hide - Non-Medable
For the non-medable armors - if they have the property 'mage armor' then you can meditate in them.
Spined/horned/barbed is only the leather modifier that is applied (each one has diff resist bonuses with barbed having the highest total points).