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How to ID Eight Common SoCal Oak Trees
Or at least convince your non-botanist friends that you know what you're talking about on your next hike.
If you walk outside in Southern California and head to the nearest tree, odds are pretty good it’ll be an Oak. Oaks are the most common tree in the state, but they can be surprisingly tricky to identify. There are around 600 species of Oak around the globe, and 3 dozen distinct species in California alone. For a recreational plant ID-er like me, that is simply too many Oak Trees to learn.
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Although botanists seem certain there are observable distinctions between all 600 Oaks, I am not so sure. Defining characteristics amongst Oaks seem murky at best, and sometimes downright cryptic. Laid out side by side in a scientific diagram, picking out the differences is easy. But introduce the variable elements of actual nature, and suddenly every Oak looks like a 3rd grader’s rendition of a tree.
Nevertheless, here is my guide to convincing your non-botanist friends that you can identify the eight most common Oaks in Southern California.
Results may vary.
Is It An Oak Tree?
First things first — is it even an Oak tree? The dead giveaway is acorns: if it has acorns, it is an Oak. Boom, case closed. Oaks are the only tree that produce acorns, and every species of Oak produces them. Some are narrow, others are stubby. Experts can identify Oaks by their acorns alone, but to be honest they all kind of look the same to me. The main takeaway here is that acorns = Oaks.
Here’s the catch: Oaks don’t begin producing acorns until they reach maturity, which doesn’t happen until the tree is 20-30 years old. The other catch is that in drought years, which is pretty much every year in Los Angeles, Oaks produce few or zero acorns at all, instead directing their energy toward self-preservation. Another caveat is that Oaks drop their acorns in the fall and don’t grow them again until Spring, so if you’re hiking in the winter none of the Oaks will have acorns.
Masters of deception, those Oak trees. If you don’t see any acorns, it still might be an Oak, or maybe not. You’ll have to do some more sciencing.
Lobed or Oval Leaves?
Lobes are a big distinction in the Oak world! Globally, the vast majority of Oaks have distinct lobes on their leaves. But here in SoCal, lobed vs. oval leaves is an easy way to divide our Oaks into two major categories. If the leaves are lobed, you’re looking at a Valley Oak, Oregon White Oak, California Black Oak, or Blue Oak. If the leaves are rounded ovals, you’re either looking at one of the three varieties of Live Oak or the extremely rare Engelmann Oak.
That is, if you’re looking at an Oak at all. Lots of other trees also have oval leaves — it’s like the most common leaf shape. And even the prickly edges of Live Oaks have many doppelgangers, like Toyon or Japanese Holly.
Most people don’t know the difference though, so if you proudly declare “check out this neat live oak” on your next hike while you point to a Holly bush, your friends will still be impressed. If one of them questions your ID and points out the distinct red holly berries, simply put on a straight face and say those are what developing acorns look like. They’ll be none the wiser.
Oaks with lobed leaves are deciduous, which means they drop their leaves in the fall and grow new ones again in the spring. Oaks with oval leaves are Live Oaks, which means they keep green leaves on their branches year round.
Here’s the thing — in Southern California where it’s nice and warm, many deciduous Oaks forget they are deciduous and end up keeping their leaves year round like their Live Oak cousins. So, yeah, thanks for nothing, Oaks. I guess the rules don’t apply to you.
Valley Oaks vs. Blue Oaks
Valley Oaks are the largest California Oaks out there, so if you’re looking at an Oak tree thinking “hot damn, that’s a big-ass oak tree” there’s a good chance it’s a Valley Oak. Except when it’s a Blue Oak instead, which on average are only slightly smaller than Valley Oaks. Unless you’re hiking around with a measuring tape and very tall ladder, it will be difficult to tell for sure.
Science says you can tell it’s a Blue Oak because the leaves are blue-gray rather than a dark waxy green. Unless of course they are covered in dust, which tends to happen a lot outside, at which point it becomes difficult to tell what color the leaves are. When you’re not sure, just go with Valley Oak and hope nobody starts wiping dust off the leaves to prove you wrong.
Oregon White vs. California Black
With names as different as black and white, you’d think these two varieties would be easier to tell apart. White Oaks generally have rounder tips to their lobes while Black Oaks come to points. Framed as a multiple choice test, it’s a piece of cake. Left as a short-answer field out in the wild, it’s a head scratcher that will leave you wondering just how pointy a lobe has to be to be considered pointy.
There’s one slightly more apparent way of distinguishing between White Oaks and Black Oaks: acorn caps. The scales of Black Oak acorn caps form a fringed edge where they hug the acorn body, while White Oak acorn caps end in a straight line around the acorn.
Honestly at this point, making your best guess and speaking up with confidence will probably work. If you hike fast enough, none of your friends will have time to fact check you anyway.
Coast Live Oak vs. Interior Live Oak vs. Canyon Live Oak
Let’s get the easy one out of the way: if you’re in a canyon, it’s probably a Canyon Live Oak. Even if it technically isn’t, nobody is going to question you when you stop and say “wow what a beautiful Canyon Live Oak” while hiking through a canyon. Canyon Live Oaks often look more like scrubby bushes than trees, and the steeper the terrain the more sure you can be.
While you might be tempted to apply the same logic to Coastal Live Oaks and Interior Live Oaks, their territories overlap over the entirety of Los Angeles. The main way botanists claim you’re able to tell them apart is by their leaves — Coastal Live Oaks supposedly have cupped, curved leaves, while Interior Live Oaks have flat leaves. If I’m being honest, they look pretty much the same to me.
These Oaks are incredibly rare, and only remain in small populations in San Diego, Riverside, and Pasadena. If you are not in one of those locations, you are probably not looking at an Engelmann Oak. Like the blue oaks, Engelmann’s have bluish tinted leaves. Like the Live Oaks, their leaves are ovals, but with one key difference: the edges are smooth.
I don’t have any jokes for Engelmann’s — they’re just plain awesome trees.
While you’re sure to find these eight Oaks out and about in Southern California, there are still 28 other species out there rooting about, which means your odds of IDing these Oaks correctly are pretty slim. But I bet your friends don’t know those species either, and if you speak confidently and make eye contact you’ll be the tree ID pro of your hiking group in no time.
(for further learning, follow the links to CalScape.org — one of the best online resources for native California plants)
Valley Oak - Big ol’ tree with deeply lobed leaves and long pointed acorns. Very common. When in doubt, go with this one.
Blue Oak - Slightly smaller big ol’ tree with lobed leaves and long pointed acorns. Blueish-gray tint to the leaves, but frequently mixed up with Valley Oaks
Oregon White Oak - Lobed leaves with rounded tips, straight line across the acorn cap.
California Black Oak - Lobed leaves with pointy tips, fringed edges where acorn cap wraps around the acorn.
Coast Live Oak - Oval leaves with prickly edges. Leaves are cupped and edges curl inward.
Interior Live Oak - Oval leaves with prickly edges. Leaves are flat, slightly more elongated.
Canyon Live Oak - Located in canyons. Oval leaves, prickly edges. Often looks more like a shrub than a tree.
Engelmann Oak - Oval leaves, smooth edges with bluish tint to them. Older trees have gnarled trunks and winding, swooping branches. Only remaining populations are located in San Diego, Riverside, and Pasadena.