* fanleaf
* or ** lemonbush
** or *** bamboo
*** maple
--> rare oak
*** pipe cactus
** pear cactus
* ball cactus

Match the stars (one before and one after the rare oak on the list) with Citrus plants and you'll get a Citrus Rare Oak. (.e. a lemonbush and pear cactus or bamboo and pear cactus)

And yes, then crossing a Venoumous Rare Oak with a Citrus Rare Oak will get you a Mela Rare Oak.