Black walnut

The Black Walnut is the tallest of twenty species of the Juglans genus worldwide of which six that are native to North America. The Black Walnut tree is a very valuable tree; it's a large, straight-stemmed timber tree with an open crown. When it's grown in the open it is a short trunked, low-branching, wide-spreading tree. It's widely planted for its nuts, lumber, and for ornamental purposes. It is found over the eastern United States as far west as Nebraska, Kansas and Texas.

Anatomy
The Black Walnut Tree is a huge tree with heights of 100-130 feet. The bark is a grey-black color and deeply split into narrow rough ridges. They are characterized by distinctive compound leaves that have an odd number of pointed, leaflets. The Black Walnut Tree has large compound leaves, 12-24 inches long with 15-23 leaflets. The leaf stems are covered with tiny fine hairs, but are smoother than butternut. The leaflets are 2-1/2 to 3 inches long, yellowish green in color, tapering at the end and toothed along the margin. The twigs on a Black Walnut are brownish, stout, blunt and with prominent leaf scars. The pith is cream colored and chambered, dividing into thin plates to segments. The fruit that the Black Walnut Tree produces is a large, rounded, brownish black nut with a hard, thick, finely ridged shell enclosing a rich, oily kernel. The kernel is edible and highly nutritious. The nut is enclosed in a solid, non-splitting husk, and is usually produced on the tree singly or in pairs. The thick bark is a dark brown and is divided by deep fissures into rounded ridges. It will have a chocolate brown color when or if the bark is broken from the tree. 

Reproduction
The Black Walnut tree produces a chemical substance called juglong (which from the genus name Juglans) that is toxic to other plants. The toxin, (5-hydroxy-alphanapthaquinone) is produced mainly by the roots which extend outward from the trunk of the tree to a distance of up to 80 feet.

Many plants are affected by the chemical, notably tomato, potato, blackberry, blueberry, mountain laurel, rhododendron and apple' injury or death resulting from an exposure of several months. Animals, notably horses, are also affected by juglone. Small amounts of walnut chips or sawdust in bedding can result in laminitis, an inflammation of the layers, or laminae, of the hooves. 

Black Walnut trees are monoecious; both female and male flowers living on the same tree they are noted for their fruit, an oil-rich nut in a ridged, hard black shell surrounded by a thick green non-splitting husk and for their hard, durable heartwood. The male flowers are in drooping catkins usually 8-10 cm long, the female flowers terminal, in cluster of two to five, ripening in the autumn into a fruit with a brownish-green, semi-fleshy husk and a brown corrugated nut. The whole fruit including the husk, falls in October, the seed is relatively small and very hard. 

Ecology
The Black Walnut Tree is native to eastern North America, west to southeast South Dakota, south to Georgia, northern Florida and southwest to central Texas. The Black Walnut tree grows mostly alongside rivers in fertile soils in mixed hardwood forests. They also grow well in pastures, meadows, and slopes. They usually appear as scattered trees or in small groves. Black Walnut tree roots transmit a growth-inhibiting chemical which keeps many other trees and plants and even its own kind from growing near it.