The Matilija Poppy or Tree Poppy (Romneya Harvey) is a poppy of southern California and northern Mexico, belonging to the Poppy family (Papaveraceae).

They are perennial subshrub with a woody stem. They may grow to a height of 2.5 meters (8 ft) and a width of 1 m (35 in), with the flowers up to 13 cm (5 in) across. The silvery greenleaves are deeply cut, with a small fringe of hairs at the margin.

They are notable for their large white flowers with intense yellow centers, blooming in summer. These flowers prefer a warm, sunny spot and fertile soil with good water drainage. They are not easily grown, but then also difficult to remove.

The genus includes only two species:

• Coulter's Matilija poppy (Romneya coulteri) Harvey
• Bristly Matilija poppy (Romneya trichocalyx) Eastwood - some consider this a variant Romneya coulteri var. trichocalyx

Matilija poppy at Strybing Arboretum, San Francisco