Acorn Species Identification Guide

Oaks are practically everywhere, and with over 400 species worldwide (and about 90 in the USA), there are a whole lot of different acorn varieties out there.

Each acorn is like a fingerprint for its oak tree. They come in various shapes, sizes, and colors! This guide will help you identify the characteristics of the main acorn species and understand their differences.

How to Identify Different Acorn Species

To crack the acorn identification code, you’ll want to focus on a few key features: length, cups (those cute little hats!), color, and overall shape.

Length

Acorns come in a surprising range of sizes. Some acorn varieties are so small they measure less than half an inch (1.2 cm). Other species are giants of the acorn world, reaching 3 inches (7.5 cm) long.

Cups

The acorn cup, or “hat,” is an important clue to its identity! Here’s what to look for:

• Scale Check: Some acorns have delicate and thin scales on their cups, while others have thick ones.
• Overlapping Scales: In North America and Europe, the cup scales will overlap like roof shingles.
• Thick or Thin Cups: The thickness of the cup itself can be another key feature, varying between species.
• Size and Coverage: Some acorn varieties have cups that cover half their length, while others have just a tiny one.
• Hairs: Certain species have hairy cups. These hairs can be differ in length, texture (from coarse to smooth), and density.

Color

Acorns often have variations of brown coloring that can provide essential clues for differentiating acorn species. Pay close attention to the specific shade – is it a dark, rich brown, a lighter tan, or perhaps with hints of red or black?

Shape

Acorns exhibit a variety of shapes depending on their species. For easy classification, we can broadly divide them into two groups:

Round (or Nearly Round): These acorns have a more circular appearance, often with a dull tip.
Elongated (Oblong/Ovoid): These acorns are distinctly longer than they are wide, possessing an elliptical shape. They typically feature a sharper, more pointed tip.

Red and White oak groups

In addition to the individual species, acorns can be broadly categorized based on whether they come from a red oak or white oak tree.

White oak acorns are usually larger and heavier than those of red oaks. But there are some exceptions to this rule. Some red oak species also produce surprisingly large acorns.

Identifying Common Acorn Species

Now that we’ve got the basics down, let’s have a closer look at the traits of specific acorns. There are way too many species to cover, but we’ll take a look at the most common ones and the features that make them unique.

Coast Live Oak Acorn (Quercus agrifolia)

Size: Up to 1.4 inches (35mm) long
Cup: Features thin, flat scales covering approximately 1/4 of the nut
Color: Reddish-brown, often with darker stripes
Shape: Conical
Oak Group: Red

White Oak Acorn (Quercus alba)

Size: Up to 1 inch (25 mm) long
Cup: Light gray with a slightly fuzzy texture (pubescent – having a covering of fine, short, soft hairs), covers approximately 1/4 of the nut.
Color: Light brown
Shape: Oblong
Oak Group: White

Sawtooth Oak Acorn (Quercus acutissima)

Size: Up to 1 inch (25mm) long
Cup: Features distinctive recurved scales (curling outwards), covers roughly ⅔ of the nut
Color: Brown
Shape: Oval
Oak Group: White

Arkansas Oak Acorn (Quercus arkansana)

Size: Up to ⅝ inch (16mm) long.
Cup: Distinctive goblet shape with pubescent scales, covering approximately ½ of the nut.
Color: Brown
Shape: Elliptical
Oak Group: Red

Bastard White Oak Acorn (Quercus austrina)

Size: Up to ⅝ inch (16 mm) long
Cup: Goblet-shaped, with gray scales, covering approximately ½ of the nut
Color: Brown
Shape: Ovoid
Oak Group: White

Swamp White Oak Acorn (Quercus bicolor)

Size: Up to 1 ¼ inches (32 mm) long
Cup: Grayish-green scales covered with fine gray hairs (tomentum), covering up to ½ of the nut
Color: Light brown
Shape: Oblong or ovoid
Oak Group: White

Boynton Oak Acorn (Quercus boyntonii)

Size: Up to ⅝ inch (16 mm) long
Cup: Pubescent, gray, covering approximately ½ of the nut
Color: Light brown
Shape: Ovoid with a rounded tip
Oak Group: White

Chapman Oak Acorn (Quercus chapmanii)

Size: Up to ½ inch (13 mm) long
Cup: Features gray tomentum (dense, short hairs) on scales, covering up to ½ of the nut
Color: Light brown
Shape: Oval with a rounded apex
Oak Group: White

Scarlet Oak Acorn (Quercus coccinea)

Size: Up to ⅞ inches (22 mm) long
Cup: Glossy with dark tones of red and brown, covering approximately ½ of the nut
Color: Light brown
Shape: Bluntly oblong
Oak Group: Red

Northern Pin Oak Acorn (Quercus ellipsoidalis)

Size: Up to ¾ inches (19 mm) long
Cup: Grayish-brown or reddish-brown, with pubescent scales
Color: Light brown
Shape: Elliptical to ovoid
Oak Group: Red

Southern Red Oak Acorn (Quercus falcata)

Size: Up to ⅝ inch (16 mm) long
Cup: Thin, reddish-brown scales, covering up to ⅓ of the nut
Color: Brown
Shape: Round
Oak Group: Red

Sand Live Oak Acorn (Quercus geminata)

Size: Up to 1 inch (25 mm) long
Cup: Whitish or gray scales, which can be smooth or pubescent, covering approximately ⅓ of the nut
Color: Dark brown
Shape: Ovoid or barrel-shaped
Oak Group: White

Georgia Oak Acorn (Quercus georgiana)

Size: Up to ½ inch (13 mm) long
Cup: Short-stalked, featuring thin, slight pubescent scales, covering approximately ⅓ of the nut
Color: Light brown
Shape: Subglobular (nearly round)
Oak Group: Red

Laurel Oak Acorn (Quercus hemisphaerica)

Size: Up to ½ inch (13 mm) long
Cup: Scales with fine hairs (pubescence), covering up to ⅓ of the nut
Color: Dark brown to black
Shape: Ovoid to hemispherical
Oak Group: Red

Bear Oak Acorn (Quercus ilicifolia)

Size: Up to ⅝ inch (16 mm) long
Cup: Features reddish-brown, moderately pubescent scales, covering up to ½ of the nut
Color: Light brown with faint stripes
Shape: Ovoid
Oak Group: Red

Shingle Oak Acorn (Quercus imbricaria)

Size: Up to ¾ inch (19 mm) long
Cup: Varies from tan to reddish-brown, with a subtly hairy texture (pubescent), covering up to ½ of the nut
Color: Chestnut-brown with faint stripes and rings around the apex
Shape: Nearly round
Oak Group: Red

Bluejack Oak Acorn (Quercus incana)

Size: Up to ⅝ inches (16 mm) long
Cup: Features reddish-brown scales that appear faintly fuzzy (pubescent), covering approximately ½ of the nut
Color: Brown with faint stripes
Shape: Oval
Oak Group: Red

Florida Oak Acorn (Quercus inopina)

Size: Up to ⅝ inch (16 mm) long
Cup: Features subtly pubescent scales, covering approximately ½ of the nut
Color: Dark brown
Shape: Oval to elliptical
Oak Group: Red

Turkey Oak Acorn (Quercus laevis)

Size: Up to 1 ⅛ inch (29 mm) long
Cup: Pubescent scales with distinctive red margins, covering up to ⅓ of the nut
Color: Light brown with faint stripes
Shape: Broadly elliptical
Oak Group: Red

Swamp Laurel Oak Acorn (Quercus laurifolia)

Size: Up to ⅝ inch (16 mm) long
Cup: Scales are pubescent, covering approximately ¼ of the nut
Color: Dark brown
Shape: Nearly round
Oak Group: Red

Overcup Oak Acorn (Quercus lyrata)

Size: Up to 2 inches (51 mm) long
Cup: Distinctive gray and pubescent scales that almost completely enclose the nut
Color: Light brown
Shape: Ovoid or oblong
Oak Group: White

Bur Oak Acorn (Quercus macrocarpa)

Size: Up to 2 inches (51 mm) long
Cup: Features distinctive large, grayish pubescent scales, covering up to ⅞ of the nut.
Color: Light brown
Shape: Broadly elliptical
Oak Group: White

Blackjack Oak Acorn (Quercus marilandica)

Size: Up to ¾ inches (19 mm) long
Cup: Reddish-brown, with pubescent scales, covering up to ⅔ of the nut
Color: Brown with faint stripes
Shape: Long and elliptical
Oak Group: Red

Swamp Chestnut Oak Acorn (Quercus michauxii)

Size: Up to 1 ⅜ inches (35 mm) long
Cup: Brown, pubescent scales, cover up to ½ of the nut
Color: Light to dark brown
Shape: Ovoid
Oak Group: White

Dwarf Live Oak Acorn (Quercus minima)

Size: Up to 1 inch (25 mm) long
Cup: Grayish scales, covering approximately ½ of the nut
Color: Dark brown
Shape: Oval
Oak Group: White

Chestnut Oak Acorn (Quercus montana / Quercus prinus)

Size: Up to 1 ½ inches (38 mm) long
Cup: Gray scales with red tips, slightly fuzzy (pubescent), covering approximately ½ of the nut
Color: Chestnut-brown
Shape: Long and oval
Oak Group: White

Notes:

• Quercus montana and Quercus prinus are currently considered the same species by reliable sources, including Britannica.
• The name Quercus montana is generally preferred, while the taxonomic status of Quercus prinus remains somewhat debated.

Chinkapin Oak Acorn (Quercus muehlenbergii)

Size: Up to 1 inch (25 mm) long
Cup: Thin, with a grayish, fuzzy texture (pubescent), covers up to ½ of the nut
Color: Light brown
Shape: Oblong to ovoid
Oak Group: White

Myrtle Oak Acorn (Quercus myrtifolia)

Size: Up to ½ inch (13 mm) long
Cup: Distinctive goblet shape, with gray, pubescent scales, covering approximately ⅓ of the nut
Color: Dark brown
Shape: Almost round
Oak Group: Red

Water Oak Acorn (Quercus nigra)

Size: Up to ⅝ inch (16 mm) long
Cup: Shallow, pubescent, covering approximately ¼ of the nut
Color: Almost black, some may have faint stripes
Shape: Almost round
Oak Group: Red

Oglethorpe Oak Acorn (Quercus oglethorpensis)

Size: Up to ¾ inch (19 mm) long
Cup: Small, with gray, pubescent scales, covering approximately ⅓ of the nut
Color: Dark brown
Shape: Ovoid
Oak Group: White

Cherrybark Oak (Quercus pagoda)

Size: Up to ⅝ inch (16 mm) long
Cup: Features chestnut-brown, pubescent scales, covering up to ½ of the nut
Color: Brown
Shape: Round
Oak Group: Red

Pin Oak Acorn (Quercus palustris)

Size: Up to ⅝ inch (16 mm) long
Cup: Features reddish-brown, thin, smooth scales, covering up to ¼ of the nut
Color: Light brown, some may have stripes
Shape: Round
Oak Group: Red

Willow Oak Acorn (Quercus phellos)

Size: Up to ½ inch (13 mm) long
Cup: Shallow, with pubescent scales, covering up to ⅓ of the nut
Color: Brown with faint stripes
Shape: Oval
Oak Group: Red

Dwarf Chinkapin Oak Acorn (Quercus prinoides)

Size: Up to ¾ inch (19 mm) long
Cup: Thin, with gray, pubescent scales, covering approximately ⅓ of the nut
Color: Light brown
Shape: Oblong to oval
Oak Group: White

English Oak Acorn (Quercus robur)

Size: Up to 1 inch (25 mm) long
Cup: Slight pubescent scales, covers up to ⅓ of the nut
Color: Light to reddish brown
Shape: Oval, elongated
Oak Group: White

Northern Red Oak Acorn (Quercus rubra)

Size: Up to 1 ¼ inches (32 mm) long
Cup: Shallow, with reddish-brown, pubescent scales, covering up to ½ of the nut
Color: Brown with gray stripes
Shape: Oblong to oval
Oak Group: Red

Shumard Oak Acorn (Quercus shumardii)

Size: Up to 1 ¼ inches (32 mm) long
Cup: Features thick, blunt scales, covering up to ⅓ of the nut
Color: Brown
Shape: Ovoid to oblong
Oak Group: Red

Swamp Post Oak Acorn (Quercus similis)

Size: Up to ¾ inch (19 mm) long
Cup: Rounded, with pubescent scales, covering approximately ½ of the nut
Color: Light brown or chestnut-brown
Shape: Ovoid to barrel-shaped
Oak Group: White

Bastard Oak Acorn (Quercus sinuata)

Size: Up to ¾ inch (19 mm) long
Cup: Shallow, with gray scales, covering up to ¼ of the nut
Color: Light brown or chestnut-brown
Shape: Ovoid or oblong
Oak Group: White

Post Oak Acorn (Quercus stellata)

Size: Up to ¾ inch (19 mm) long
Cup: Thin, with gray, pubescent scales, covering up to ⅔ of the nut
Color: Light brown, sometimes with faint stripes
Shape: Round
Oak Group: White

Texas Red Oak Acorn (Quercus texana)

Size: Up to 1 inch (25 mm) long
Cup: Thin, goblet-shaped, with pubescent scales, covering approximately ½ of the nut
Color: Chestnut-brown with faint stripes
Shape: Egg-shaped
Oak Group: Red

Black Oak Acorn (Quercus velutina)

Size: Up to ¾ inch (19 mm) long
Cup: Thick, reddish-brown, with pubescent scales, covering up to ½ of the nut
Color: Light reddish-brown
Shape: Ovoid to elliptical
Oak Group: Red

Southern Live Oak Acorn (Quercus virginiana)

Size: Up to 1 inch (25 mm) long
Cup: Deep goblet-shaped, with light gray scales featuring reddish tips, pubescent, covering approximately ½ of the nut
Color: Dark brown to nearly black
Shape: Narrowly oblong
Oak Group: White

Conclusion

Now you’re an acorn identification pro! Remember, practice makes perfect. The next time you discover acorns on the ground, take a closer look. Use your knowledge of size, cups, color, shape, and oak group to see if you can determine their species.

With careful observation and this guide’s help, you’ll never look at acorns the same way again.

Sources:
Field Guide to Native Oak Species of Eastern North America – Forest Health Technology Enterprise Team