Coast or Interior Live Oak?
by Bruce Homer-Smith

Coast Live Oak (Quercus agrifolia) and Interior Live Oak (Quercus wislizeni) look very similar. Distinguishing between them in the field is not always possible since their leaf shapes vary greatly, their ranges overlap, and they hybridize.

However there are characteristics to look for that will sometimes tell you, and they’re fun to look for:

Underside of Leaves:

Photo © Keir Morse - Underside of a Coast Live Oak leaf

Photo Julie Kierstead Nelson - Interior Live Oak Leaves

Hairy Armpits – Many Coast Live Oak have tiny brown hairs at vein junctions on the underside of leaf. Interior Live Oaks never do.

Leaf Curls Under – Coast Live Oak leaves often curl under if the tree is under stress (most trees are to some extent). However, individual Interior Live Oaks leaves may curl under as well. This characteristic is a more a hint than a defining difference.

Lateral Vein Count – Coast Live Oaks generally have 5 or fewer pairs of veins connecting to the mid vein. Interior Live Oaks generally have 5 or more. (Source: http://cemarin.ucdavis.edu/Programs/Custom_Program97/Types_of_oaks/Red_Oaks/)

Acorn Location:

Coast Live Oak acorns mature in one year. Since they grow from a flower nestled at the base of a leaf, brown mature acorns appear among this year’s leaves.

Photo Toni Corelli – Mature Coast Live acorns nestled in this year’s leaves.

Interior Live Oak acorns take two years to mature. They’ll show green the first year, but mature brown acorns will generally show behind this year’s leaf growth.

Corrections/Comments: bruce@PlantID.net