Thursday, October 15, 2009

LOOK FOR: Acorns of many shapes and sizes - an identification guide for 12 common oak species

There are 90 species of oak in North America. Their acorns are an important food for a broad diversity of wildlife, from insects to deer. And historically, they were a staple food for Native Americans in this area.

Oaks are generally split into two groups: "red" and "white." Red oaks have leaves whose lobes come to a point, with a little bristle on each point. Their acorns take two years to mature, so even as they're dropping this year's crop, they've already got half-grown acorns for next year. White oaks have leaves with more rounded lobes, typically lighter-colored bark, and their acorns take only one year to mature. But even within those two groups, there's a wonderful diversity of acorn shapes and sizes. Below are a selection of some of the acorns you might see in the greater DC area. (We've tried to line them up so they're to scale.) How many can you find in the wild?

Red Oaks

Northern Red Oak
Quercus rubra
Southern red oak
Quercus falcata
Black oak
Quercus velutina

Willow Oak
Quercus phellos
Pin oak
Quercus palustris
Blackjack oak
Quercus marilandica

White Oaks

White oak
Quercus alba
Overcup oak
Quercus lyrata
Swamp white oak
Quercus bicolor

Chestnut oak
Quercus prinus
Post oak
Quercus stellata
Bur oak
Quercus macrocarpa

One way to really get familiar with acorns is to collect them for Growing Native. The Potomac Conservancy will use them to replant buffer zones along the Potomac and its tributaries. This improves water quality and provides important wildlife habitat. You can donate collected acorns until October 26 in Virginia and October 31 in  Maryland and DC.

All photos by Steve Hurst at the amazing USDA-NRCS PLANTS Database, except the post oak acorns, which are from the magnificent old tree here at The Natural Capital headquarters.