This is specifically concerning the middle evolution, and not the first or second stages.
Ivysaur (Grass)
Charmeleon (Fire)
Wartortle (Water)
Bayleef (Grass)
Quilava (Fire)
Croconaw (Water)
Grovyle (Grass)
Combusken (Fire)
Marshtomp (Water)
Grotle (Grass)
Monferno (Fire)
Prinplup (Water)
Servine (Grass)
Pignite (Fire)
Dewott (Water)
Quilladin (Grass)
Braixen (Fire)
Frogadier (Water)
Dartrix (Grass)
Torracat (Fire)
Brionne (Water)
So which seven of these make your list? (:
[spoiler]I made the image myself using a mobile app, so it may be poor quality.[/spoiler]
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Wartortle Quilava Grovyle Grotle Only going up to Gen 4 because I don't care about the later installments.