Walnut trees are monoecious, meaning a single tree contains both male (catkin) and female (pistillate) flowers, allowing them to self-pollinate. However, nut production is best when walnut trees of different cultivars are planted in groups, as is typically done in walnut groves cultivated for nut... MORE production.
"The shadow of the walnut tree is poison to all plants within its compass." --Pliny the Elder (23-79 CE) This imposing tree is located in the gaggle of trees behind 245 Prospect. Unsurprisingly enough, the Eastern Black Walnut is most well known for the fruit it produces--the walnut.
The English walnut, (Juglans regia) also known as Persian walnut, is the most commonly grown walnut for nut production. The Northern California black walnut (Juglans hindsii) and the hybrid ‘Paradox’ (J. hindsii x J. regia) are used primarily as a rootstock for the English scion.