If you see acorns on the ground, look up: it's probably Red Oak

The local oaks have begun dropping their acorns, and stately Northern Red Oak (Quercus rubra) is first.  Since oaks are rather tricky things to destinguish, it's handy to be able to use this time to pick them out of the crowd.

The many species of oaks come in two basic flavors (subgenera or "sections") here in eastern North America: those with round-lobed leaves, and acorns that mature in one growing season and are more sweet-tasting with acorn cups hairless inside, called the "white oak group"*; and those with bristle-lobed leaves, and bitter acorns that need two growing seasons to mature and have cups hairy on the inside, called the "red oak group." 

Red Oak has leaves that are generally "more leaf than hole," while roughly-similar black, scarlet and pin oaks are often "more hole than leaf."  In Red Oak the acorn cap covers only the end of the nut, whereas other local trees in its group have caps that surround much more.  (White Oak, which will begin dropping acorns soon, has nuts with a similar "beret," but these are easy to distinguish, since that beret has a very bumpy surface, unlike the nearly smooth caps of Red Oak.)

Red Oak branchlet with a mature acorn begun last spring, and tiny acorns (looking a bit like buds) in pairs in the axil of each leaf.  (A bite mark on the end shows a bad-mannered squirrel cut it down.)

 

 

If reproduction is a chancy business in the best of circumstances, it is much more so for a city tree.  Car tires and shoe soles end the careers of  many oak babies once they've fallen.

Northern Red Oak is an important forest tree throughout the eastern US, and its acorns--bitter though they are--are food for many animals.  It is the only one of its local sibling species that has bark with stripes that run all the way down the trunk--even on large trees. 


*This also includes Southern Live Oak, the famous deep South tree iconically Spanish moss covered.  It has entire (unlobed) leaves that are green almost year-round.  (If you want to see Live Oak here, visit Old Ironsides in Boston Harbor: it is framed and planked with its tough, dense wood.)

Mighty Oaks from Acorns Grow

Once every few days or week I log into Nature's Notebook (NN) to continue my contribution to citizen science.  NN is a long-term project of the National Phenology Network, in which ordinary citizens track seasonal changes in plants and animals nationwide, to provide data to scientists interested in, for example, the rate at which climate is changing, and how living things are adapting--or not.  Most of the half-dozen or so species I track in my neighborhood are trees, and big trees, at that.  So I am mildly frustrated to come to the following questions on the data sheet: Do you see pollen release?  Do you see fruits?  Do you see ripe fruits?  The fact is I seldom see any of these, mainly because they are too too far away up in the tree's canopy.

A thunderstorm last night finally wetted the dusty ground here and might perk up the wilted leaves for a day, but it had another helpful side effect: it knocked down a few twigs from a majestic but inaccessible red oak on the other side of my block. Finally I got a look at something I seldom see: baby acorns.  

 

Branchlet of red oak (Quercus rubra).  The developing acorns are invisibly small here, 

but you can make them out in the photo below.

 

Here are three or four acorns in the axils of the leaves, while buds (for comparison) are at the tip of the twig.

When I first saw these on a fallen twig a few weeks ago, I first thought they were deformed buds.  I had to stare at them awhile and finally decided they must be acorns. 

 

 The previous photo, cropped.  At the tip of each acorn, you can just make out 

the three curly stigmas left over from the female oak flower.

The acorns are curiously small so late in the season, until you realize they will not finish maturing until next summer.  

Red oak belongs to the group of oaks that takes two years to mature its acorns.  Called the "red oak group," these oaks have leaves with pointed, bristle-tipped lobes.  Around here, they include scarlet oaks and black oaks as well as red.  

 

Scarlet oak (Quercus coccinea).  Another tree, pin oak, has similar leaves 

("more hole than leaf"), but lives in wetlands.

 

Black oak (Quercus velutina) has a leaf with fewer and broader lobes than red oak,

and is less deeply-cut than scarlet oak.

 

The acorns of red oak are broad faces wearing berets.  

The acorns of the red oak group mature the second year, so these came from last year's flowers.

 

Acorns of white oak have thinner faces wearing  knit caps.  They mature the same year, and are sweeter and more readily edible than acorns of red oak, etc.