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Tree flowers

Tree Flowers (and fruits) 

Black walnut

A common pattern for some wind-pollinated species such as oaks, hickories and walnuts, is for the pollen-producing male flowers to be individually tiny, but presented abundantly in elongate drooping finger-like catkin. Nearly on the same tree there are female flowers which are slightly larger, and much fewer in number. These eventually mature into the familiar nut or nut-like fruit.

During the spring and summer of 2006 I followed the progress of flowering on a black walnut tree (Juglans nigra, family Juglandaceae) alongside Indianola Avenue near Columbus School for the Deaf. Here is a flowering branch. This species is monoecious, i.e., the individual flowers are either male or female, but both types are borne on the same tree. Being wind-pollinated, the flowers are not showy. 

Walnut branch

Flowering branch of black walnut, May 22, 2006, Columbus OH.

Seen closer, the female flowers display pollen-receptive stigmas hat are fairly elaborate "rabbit ears" presenting a large enough surface area to be encountered by pollen drifting in the wind.

walnut female flowers

Black walnut pistillate flowers, May 22, 2006, Columbus, OH.

walnut may28walnut june 11

Black walnut very young fruits in late spring, 2006  (left: May 28, and right: June 6). By this time the spent staminate catkins have fallen to the ground.

By late summer the walnuts are almost ripe, ready to be snatched by a squirrel or fall to the ground. The great 17th-century Swedish naturalist Carolus Linneaus was the "father of systemtic botany" who developed the two-part naming system still in use today. Linneaus gave latin names to many North American plants. He must have had quite an active imagination, as he named this one "Juglans," short for "Jupiter's glands."

Walnut fruiting

Black walnut, September 20, 2006, Columbus OH.

In early autumn, black walnut fruits fall to the ground where their outer husk slowly decays. They are well-known for leaching chemicals into the soil that inhibit the growth of other plants, an ecological interaction known as "allelopathy," (literally meaning "making your neighbor sick"). Black walnuts are edible and appreciated greatly by those who somehoew manage to crack open the very thick husks. The walnut of commerce, grown mainly in California, is the English walnut, Juglans regia.

walnut fruits on the ground

Black walnut fruits on the ground (location and date unknown). The one on the left looks like a face, winking.