ak trees have male flowers on one
part of their branch, and female flowers on another part of the same branch. When a plant
bears both male and female flowers it's said to monoecious
At the right you
see a flowering branch of a Black Oak, Quercus velutina, from a
tree in southern Mississippi. It was scanned in mid March just as the tree's leaves and
flowers were appearing. The leaves in the picture are only about one-fifth their summer
If you don't know what a calyx or a stamen is, you can review these items on our Standard Blossom Page. The yellow, wormlike items
in the picture's lower, left corner are catkins, more technically known
as aments. Catkins are clusters, or inflorescences, of male flowers.
Each of the "bumps" on the catkins is a male flower consisting of a
bract (a highly modified leaf), a lobed calyx and some
pollen-producing stamens. Once the stamens have released their pollen
into the air, the entire catkin will fall from the tree. Maybe you've seen thousands of
such spent catkins littering a sidewalk beneath an oak tree early in the spring. Other
trees producing catkins include willows and birch.
IDENTIFICATION KEYS IN
FLORA OF NORTH AMERICA
In North America you can "key to species level" your unknown oaks at the Flora of North America website. Go to the key near the bottom of the
page you arrive at when you click the above link, figure out your unknown oak's
"section," click on that section, and then key out your unknown to species level
using the resulting key. These are technical keys using technical terms, but they are very
useful. Often you'll need acorns during the keying process.
On a flowering oak twig you have to look close to see the female flowers -- the
future acorns. The inset in the picture's lower right corner shows a
much-magnified female flower. Actually, mainly you just see the reddish 3-lobed stigma.
Below the stigma there's an egg-shaped ovary camouflaged so well that it
blends with the fuzzy petiole beneath it, and the fuzzy stem just to its left. Since these
female flowers appear where you might expect a bud to be most people overlook them,
thinking they are seeing buds. However, a bud would never be topped with a 3-lobed stigma!
There are dozens of species of oaks and they can all be divided into two great groups,
depending on how long it takes for its female flowers to develop into acorns. Acorns in
the White Oak Group mature the year they appear, and the acorn's kernel
is often sweetish and edible. The Chestnut Oaks belong to this group.
Acorns in the Red and Black Oak Group mature in their second year and
often their kernel is so bitter that a human would have a hard time eating it.