Juglans nigra is a tree to 30 m tall; bark almost black, deeply grooved, ridges rough, pith chambered, tan; leaf scars conspicuous, shield-shaped to 3-lobed, vein scars 3, often horse-shoe shaped, winter buds white-wooly; taprooted with wide lateral root spread, forms vesicular-arbuscular endomycorrhizae (Brundrett and Kendrick 1988); growth pattern indeterminate (Gargiullo personal observation).
Leaves pinnately compound, about 17 leaflets, opposite to alternate, margins toothed (end leaflet may be lacking), crushed leaves aromatic, slightly sticky; buds whitish wooly, leaf without hairy fringe; leaves expand mid-May; winter plant leafless 190 days (Britton 1874).
Flowers, catkins, sexes separate on same plant (monoecious) male on last years shoots, female on current years growth, female flowers open before male (Wyatt 1983), wind pollinated; blooms May-June.
Fruit spherical, aromatic; nuts wrinkled, hard, 2-valved, Sept.-Oct., often apparent on leafless trees in fall, eaten and dispersed by squirrels. Kernel lipid content ca 23%, protein 33% dry weight (Smith and Follmer 1972). Requires overwintering and burial for germination, may not germinate until second year.
Wetland status: NL.
Frequency in New York City: Infrequent.
Habitat: Moist, soil, in open areas, stream banks, floodplains, sometimes on fill. Prefers well drained, limestone derived soils. Tolerates pH 4.6-8.2. A pioneer species, intolerant of shade, index 4 (Hightshoe 1988), but can survive under the light shade of black locust, Robinia pseudoacacia (personal observation).
Notes: Young trees stump sprout if cut or burned. Produces allelopathic substance, juglone, especially from roots and fruit husk, toxic to other vegetation. Somewhat tolerant of flooding (more so than Prunus serotina or Carya ovata). Moderately salt tolerant. Ozone tolerant. Defoliated by walnut caterpillar (Datana integerrima) and fall webworm (Hyphantria cunea). The boring insect, ambrosia beetle, (Xylosandrus germanus) may infect trees with a Fusarium fungus (Burns & Honkala 1990). Infected by an anthracnose caused by Gnomonia leptostyla (Ascomycotina, Pyrenomycetes) which appears as tiny, round, dark lesions on leaf undersides (to 0.5 cm wide), usually surrounded by a zone of yellow, spread of these lesions eventually cause death of leaves. Nectria galligena (Ascomycotina) causes cankers that begin as small dark depressed areas on young bark. As the canker progresses it develops a target-like appearance as successive layers of callus tissue are killed and die back. Eventually it girdles and kills branches (Agrios 1988; Sinclair et al. 1987).