Druidic Theurgy

Type: General
Source: Dragon #325

You can apply knowledge gained in another spellcasting class to druid spells.
Prerequisite: Ability to cast 3rd-level druid spells, ability to cast spells from a different spell list.
Benefit: Choose a spellcasting class other than druid in which you have at least one level. For the purpose of casting spells from the druid spell list that also appear on the chosen class's spell list, your caster level equals the sum of your levels in the druid class and the chosen class. For example, a 5th-level druid/2nd-level cleric can cast spells that appear on both spell lists as a 7th-level caster.
This does not affect your spells per day or spells known. It only increases your caster level when casting the appropriate spells.
Special: You can gain this feat multiple times. Its effects do not stack. Each time you take the feat, it applies to a new non-druid spellcasting class in which you have at least one level.

Feats Finder