Answer: Keeping in mind that tree roots will compete with the roots of other plants for moisture and nutrients, and that oak roots sometimes harbor Oak Root Fungus, the following plants will probably perform well under your tree:
Artemisia, Aloe, Daylily, Heuchera (Coral Bells), Kniphofia (Red-Hot Poker), Nepeta (Catmint), Oregano, Penstemon, Sedum (Stonecrop), Cistus (Rockrose) and Rosemary.
These plants are resistant to Oak Root Fungus, and don't seem to mind the shade of oaks. Oaks do not like irrigation or disturbance within 10' feet of their trunks, so try to keep your plants outside of this area.
Enjoy your new home and garden!
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