(Southern) California black walnut

Victim of urbanisation

The southern california walnut is a deciduous bush or small tree of 6-9 m in height. The leaves are composite, and the flowers - dangling catkins - bloom from March to the end of May. It is used frequently in parks and urban woodland. The fruit is a round nut (more correctly, a drupe) with an outer fleshy green husk that opens to reveal the actual walnut - a single seed encased in a thick, hard-to-crack, shell (innermost layer of the fruit wall). Even though the nut is edible this species is not commercially grown.

Ecology and habitat

There are two varieties of the southern california walnut, var. californica and var. hindsii, both endemic to California. This species grow to altitudes of 30 – 900 m on damp, clayey soils. Native populations grow on hills and canyons, in forests and more open savannah type woodland in which this species dominated.

Threat

The natural forest area with southern california walnut is fragmented and in decline. Of the forests supporting var. hindsii especially, only two or three have survived. The prettiest walnut trees remaining can be found in the San Jose Hills. They have suffered as a result of increased urbanisation, grazing, recreation and possibly a decrease in their fecundity. For 200 years grazing was the main economic concern in the walnut forests, which has greatly affected the undergrowth and animal life. The combination of regular grazing and increased aridity is detrimental to the survival of the seedlings.