Acorn Species Identification Guide

Acorns are the nut of the oak tree. A typical acorn will contain a single seed. When cultivated, it grows into a sapling before transforming into a mature oak tree. 

Acorns grow where oaks grow. That means that they are found almost everywhere. The total number of oaks that can be found worldwide is around 400. Around 90 of them are native to the USA alone.

Each type of acorn has its unique characteristics. They have different colors, sizes, tips, shapes, and other features that make it possible for us to identify them.

This guide will make it easier to know what type of acorn you have just by analyzing its main characteristics.

How is it possible to identify the different species of acorns?

To identify a specific acorn species, we need to look at its length, cups, color, and shape.

Length

Different acorn species have distinct sizes. Some can be very small, with less than 0.5 inches (1.2 cm). But bigger varieties can grow up to 3 inches (7.5 cm) long.

Cups

The cup of the acorn, or hat, as some people call it, can also help to identify the species:

• Some acorn varieties have thin scales; some have thick ones
• In North America and Europe, the cup scales are overlapped
• The thickness of the cup itself also differs depending on the acorn species
• The cup size varies. In some species, it can cover half of the acorn 
• Some acorn species have hairs on their cup. The hairs can be long and matted, short and fine, and smooth

Color

The color is also different, depending on the acorn type. They can be dark brown, light brown, red, and black.

Shape

Acorns have different shapes and sizes depending on the species. As a rule of thumb, when it comes to shape, acorns can be categorized into two groups.

The first group includes round acorns, or almost round. It’s very common for this group to have a dull tip.

The second group refers to elongated acorns, often referred to as “oblong” and “ovoid”. These acorns have an elliptical shape. The tip on this group of acorns is sharper; it’s the typically pointed tip we associate with acorns.

Red and White oak groups

Finally, acorns can be categorized according to the group of oak from which they originate: red and white.

The white oak group generally produces larger and heavier acorns.

Identifying Common Acorn Species With Characteristics and Pictures

After classifying acorns into general categories, let’s look at some specific acorn species. Due to the vast number of species, we can’t cover all of them. But we will point out the main characteristics of the most common acorn species and show you a picture of each one, to make it easier to identify.

Coast live oak acorn – Quercus agrifolia

Size: up to 1.4 inches (35mm)
Cup: thin and flat scales, covers ¼ of the nut
Color: reddish-brown, stripes
Shape: conical
Oak group: red

White oak acorn – Quercus alba

Size: up to 1 inch (25 mm)
Cup: light gray, pubescent, covers ¼ of the nut
Color: light brown
Shape: oblong
Oak group: white

Sawtooth oak acorn – Quercus acutissima

Length: up to 1 inch (25 mm)
Cup: recurved scales, covers about ⅔ of the nut
Color: brown
Shape: oval
Oak group: white

Arkansas oak acorn – Quercus arkansana

Length: ⅝ inch (16mm)
Cup: goblet-shaped, pubescent scales, covers up to ½ of the nut
Color: brown
Shape: elliptical nut
Oak group: red

Bastard white oak acorn – Quercus austrina

Length: ⅝ inch (16 mm)
Cup: goblet-shaped, gray scales, covers up to ½ of the nut
Color: brown
Shape: ovoid nut
Oak group: white

Swamp white oak acorn – Quercus bicolor

Length: up to 1 ¼ inches (32 mm)
Cup: grayish-green, scales covered with fine gray momentum, covers up to ¾ of the nut
Color: light brown
Shape: oblong or ovoid
Oak group: white

Boynton oak acorn – Quercus boyntonii

Length: up to ⅝ inch (16 mm)
Cup: pubescent gray, covers up to ½ of the nut
Color: light brown
Shape: ovoid nut with a rounded tip
Oak group: white

Chapman oak acorn – Quercus chapmanii

Length: up to ½ inch (13 mm)
Cup: gray tomentum on scales. Covers up to ½ of the nut
Color: light brown
Shape: oval with a rounded apex
Oak group: white

Scarlet oak acorn – Quercus coccinea

Length: up to ⅞ inches (22 mm)
Cup: glossy dark, tones of red and brown, covers up to ½ of the nut
Color: light brown
Shape: bluntly oblong
Oak group: red

Northern pin oak acorn – Quercus ellipsodidalis

Length: up to ¾ inches (19 mm)
Cup: grayish-brown or reddish-brown, pubescent
Color: light brown
Shape: elliptical to ovoid
Oak group: red

Southern red oak acorn – Quercus falcata

Length: up to ⅝ inch (16 mm)
Cup: thin, reddish-brown, covers up to ⅓ of the nut
Color: brown
Shape: round
Oak group: red

Sand live oak acorn – Geminata

Length: up to 1 inch (25 mm) 
Cup: whitish or gray scales that can be smooth or pubescent, covers ⅓ of the nut
Color: dark brown
Shape: ovoid or barrel-shaped
Oak group: white

Georgia oak acorn – Quercus georgiana

Length: up to ½ inch (13 mm)
Cup: short-stalked, thin, slightly pubescent, covers up to ⅓ of the nut
Color: brown
Shape: subglobular
Oak group: red

Laurel oak acorn – Quercus hemisphaerica

Length: up to ½ inch (13 mm)
Cup: fine pubescence on scales, covers up to ⅓ of the nut
Color: dark brown to black
Shape: ovoid to hemispherical
Oak group: red

Bear oak acorn – Quercus ilicifolia 

Length: up to ⅝ inch (16 mm)
Cup: reddish-brown with pubescent scales, covers up to ½ of the nut
Color: light brown, faint stripes
Shape: ovoid
Oak group: red

Shingle oak acorn – Quercus imbricaria

Length: up to ¾ inch (19 mm)
Cup: tan to reddish-brown, pubescent, covers up to ½ of the nut
Color: chestnut-brown, faint stripes, rings around the apex
Shape: nearly round 
Oak group: red

Bluejack oak acorn – Quercus incana

Length: up to ⅝ inches (16 mm)
Cup: pubescent, reddish-brown scales, covers up to ½ of the nut
Color: brown, faint stripes
Shape: oval
Oak group: red

Florida oak acorn – Quercus inopina

Length: up to ⅝ inch (16 mm)
Cup: pubescent scales, covers up to ½ of the nut
Color: dark brown
Shape: oval to elliptical
Oak group: red

Turkey oak acorn – Quercus laevis

Length: up to 1 ⅛ inch (29 mm)
Cup: pubescent scales with red margins, covers up to ⅓ of the nut
Color: light brown with faint stripes
Shape: broadly elliptical
Oak group: red

Swamp laurel oak acorn – Quercus laurifolia

Length: up to ⅝ inch (16 mm)
Cup: pubescent scales, covers up to ¼ of the nut
Color: dark brown
Shape: nearly round
Oak group: red

Overcup oak acorn – Quercus lyrata 

Length: up to 2 inches (51 mm)
Cup: gray pubescent scales, covers most of the nut
Color: light brown
Shape: ovoid or oblong
Oak group: white

Blur oak acorn – Quercus macrocarpa 

Length: up to 2 inches (51 mm)
Cup: grayish pubescent scales, covers up to ⅞ of the nut
Color: light brown
Shape: broadly elliptical
Oak group: white

Blackjack oak acorn – Quercus marilandica

Length: up to ¾ inches (19 mm)
Cup: reddish-brown, pubescent scales, covers up to ⅔ of the nut
Color: faintly striped
Shape: long and elliptical
Oak group: red

Swamp chestnut oak acorn – Quercus michauxii

Length: up to 1 ⅜ inches (35 mm)
Cup: brown pubescent scales, covers up to ½ of the nut
Color: light to dark brown
Shape: ovoid nut
Oak group: white

Dwarf live oak acorn – Quercus minima

Length: up to 1 inch (25 mm)
Cup: grayish scales, covers up to ½ of the nut
Color: dark brown
Shape: oval
Oak group: white

Chestnut oak acorn – Quercus montana / Quercus prinus

According to Britannica, Q. Montana and Q. Prinus are the same species. Wikipedia explains that: “The name Quercus prinus was long used by many botanists and foresters for either the chestnut oak or the swamp chestnut oak, with the former otherwise called Q. montana or the latter otherwise called Q. michauxii. The application of the name Q. montana to the chestnut oak is now accepted, since Q. prinus is of uncertain position, unassignable to either species”.

Length: up to 1 ½ inches (38 mm)
Cup: gray scales with red tips, pubescent, covers up to ½ of the nut
Color: chestnut-brown
Shape: long and oval
Oak group: white

Chinkapin oak acorn – Quercus muehlenbergii

Length: up to 1 inch (25 mm)
Cup: thin, gray pubescence, covers up to ½ of the nut
Color: light brown
Shape: oblong to ovoid
Oak group: white

Myrtle oak acorn – Quercus myrtifolia

Length: up to ½ inch (13 mm)
Cup: goblet-shaped, gray pubescence, covers up to ⅓ of the nut
Color: dark
Shape: almost round
Oak group: red

Water oak acorn – Quercus nigra

Length: up to ⅝ inch (16 mm)
Cup: shallow, pubescent, covers up to ¼ of the nut
Color: almost black, some have faint stripes
Shape: almost round
Oak group: red

Oglethorpe oak acorn – Quercus oglethorpensis

Length: up to ¾ inch (19 mm)
Cup: small, grey scales, pubescent, covers up to ⅓ of the nut
Color: dark brown
Shape: ovoid
Oak group: white

Cherrybark oak – Quercus pagoda

Length: up to ⅝ inch (16 mm)
Cup: chestnut-brown, pubescent scales, covers up to ½ of the nut
Color: brown
Shape: round
Oak group: red

Pin oak acorn – Quercus palustris

Length: up to ⅝ inch (16 mm)
Cup: reddish-brown, thin, smooth scales, covers up to ¼ of the nut
Color: light brown, some are striped
Shape: round
Oak group: red

Willow oak acorn – Quercus phellos

Length: up to ½ inch (13 mm)
Cup: shallow, pubescent scales, covers up to ⅓ of the nut
Color: brown, faint stripes
Shape: oval
Oak group: red

Dwarf chinkapin oak acorn – Quercus prinoides

Length: up to ¾ inch (19 mm)
Cup: thin, gray pubescent scales, covers up to ⅓ of the nut
Color: light brown
Shape: oblong to oval
Oak group: white

English oak acorn – Quercus robur

Length: up to 1 inch (25 mm)
Cup: covers up to ⅓ of the nut
Color: brown
Shape: oval, elongated
Oak group: white

Northern red oak acorn – Quercus rubra

Length: up to 1 ¼ inches (32 mm)
Cup: shallow, reddish-brown pubescent scales, covers up to ½ of the nut
Color: brown, gray stripes
Shape: oblong to oval
Oak group: red

Shumard oak acorn – Quercus shumardii

Length: up to 1 ¼ inches (32 mm)
Cup: thick, blunt scales, covers up to ⅓ of the nut
Color: brown
Shape: ovoid to oblong
Oak group: red

Swamp post oak acorn – Quercus similis

Length: up to ¾ inch (19 mm)
Cup: rounded, pubescent scales, covers up to ½ of the nut
Color: light brown or chestnut-brown
Shape: ovoid to barrel-shaped
Oak group: white

Bastard oak acorn – Quercus sinuata

Length: up to ¾ inch (19 mm)
Cup: shallow, gray scales, covers up to ¼ of the nut
Color: light brown or chestnut-brown
Shape: ovoid or oblong
Oak group: white

Post oak acorn – Quercus stellata

Length: up to ¾ inch (19 mm)
Cup: thin, gray pubescent scales, covers up to ⅔ of the nut
Color: light brown, sometimes it has faint stips
Shape: round
Oak group: white

Texas red oak acorn – Quercus texana

Length: up to 1 inch (25 mm)
Cup: thin, goblet-shaped, pubescent, covers up to ½ of the nut
Color: chestnut-brown, faint strips
Shape: egg-shaped
Oak group: red

Black oak acorn – Quercus velutina

Length: up to ¾ inch (19 mm)
Cup: thick, reddish-brown, pubescent, covers up to ½ of the nut
Color: light reddish brown
Shape: ovoid to elliptical
Oak group: red

Southern live oak acorn – Quercus virginiana

Length: up to 1 inch (25 mm)
Cup: deep goblet-shaped, light gray scales with reddish tips, pubescent, covers up to ½ of the nut
Color: dark brown to nearly black
Shape: narrowly oblong
Oak group: white

FAQs

Sources:
https://www.fs.usda.gov/foresthealth/technology/pdfs/fieldguide.pdf
https://edis.ifas.ufl.edu/
https://canr.udel.edu/udbg/
https://naturalresources.extension.iastate.edu/forestry
https://www.wikihow.com/Identify-Oaks-by-the-Acorns