We derive new functional equations at a species level for certain classes of 2-trees, including a dissymmetry theorem. From these equations we deduce various series expansions for these structures. We obtain formulas for unlabeled 2-trees which are more explicit than previously known results. Moreover, the asymptotic behavior of unlabeled 2-trees is established.  2002 Elsevier Science (USA) Nous présentons de nouvelleséquations fonctionnelles pour certaines classes de 2-arbres, incluant un théorème de dissymétrie. Nous en déduisons diverses séries génératrices associéesà ces espèces. Nous obtenons ainsi des formulesénumératives pour les 2-arbres non-étiquetés qui sont plus explicites que les résultats connus jusquà présent. De plus le comportement asymptotique de ces structures estétabli.

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