Oakheart Dryads

• WWizards of the Coast2014-04-26
  Official Ruling
  A constellation ability triggers whenever an enchantment enters the battlefield under your control for any reason. Enchantments with other card types, such as enchantment creatures, will also cause constellation abilities to trigger.
• WWizards of the Coast2014-04-26
  Official Ruling
  An Aura spell without bestow that has an illegal target when it tries to resolve won't resolve and will be put into its owner's graveyard. It won't enter the battlefield and constellation abilities won't trigger. An Aura spell with bestow won't be countered this way. It will revert to being an enchantment creature and resolve, entering the battlefield and triggering constellation abilities.
• WWizards of the Coast2014-04-26
  Official Ruling
  When an enchantment enters the battlefield under your control, each constellation ability of permanents you control will trigger. You can put these abilities on the stack in any order. The last ability you put on the stack will be the first one that resolves.

Rulings via Scryfall