Juglans nigra L., black walnut. Tree, winter–deciduous, with 1 trunk, in range often 10+ m tall; monoecious; shoots with variable–sized glandular hairs, the hairs with broad heads and aging yellowish, aromatic; bark brown, fissured into narrow plates.
Stems angled becoming cylindric when woody, with rounded V–shaped leaf scars having 3 prominent traces ca. 5.5 mm across; pith of young twigs chambered, 1 mm diameter, brown, with ca. 35 diaphragms per 10 mm; bark thick and furrowed, gray.
Leaves helically alternate, odd–1–pinnately compound having (9—)11—19(—23) leaflets with lateral leaflets subopposite and a diminutive terminal leaflet (absent), petiolate, without stipules; petiole not channeled but indented close to stem, in ×–section biconvex, 35—85 mm long, short–tomentose and with small, densely short–hairy next to axillary bud, stalked glandular hairs of varied lengths often with reddish heads; rachis not channeled, 250—400 mm long, pairs spaced to 50 mm apart, densely glandular–hairy; petiolules short—1.5 mm long, short–tomentose and glandular–hairy; blades of leaflets lanceolate or narrowly ovate, (40—)55—115 × 13—45 mm with the longest leaflet midleaf, lateral leaflets asymmetric + oblique and cordate at base (indented on leading edge), low–serrate (subentire) on margins, acuminate to acute at tip, pinnately veined with principal veins somewhat raised on both surfaces, upper surface glabrous, lower surface glandular–hairy and when young with shaggy hairs mostly in axils between midrib and lateral veins.
Staminate inflorescence catkin (ament), racemelike, clustered, many–flowered, preformed during previous year and emerging before leaves from winter buds below new growth, shedding pollen several months later with mature leaves present, lax and pendent, long–cylindric, to 100 mm long, with radiating, nodding flowers 6—7 per 10 mm on pedicel–like axes, glabrous or with several hairs approaching each pedicel, becoming mostly glabrescent before anthesis; peduncle absent; pedicel–like axes spreading, at anthesis sparsely hairy; bractlet subtending flower acuminate–ovate, 0.7—1.1 mm long, on the oldest, sterile nodes of catkins without pedicel and heart–shaped, ca. 1.5 × 1.5 mm, reddish, hairy, subtending 2 bracteoles, the bracteoles sepal–like and indistinguishable from sepals; axis to 1.5 mm long, exlarged at top, with scattered branched hairs.
Staminate flower 3.3—4.5 mm across; on green, dishlike receptacle; perianth (calyx) mostly 6–lobed, fused at base to receptacle, green; lobes subequal, obovate to roundish, mostly 1.5—2 mm long, stringing curved inward cupping anthers; stamens 25—35, attached to receptacle; filaments short; anthers exserted, basifixed, dithecal, 0.8—1.7 mm long, distinctly 4–lobed, greenish yellow, with light green on connective and a fleshy, shallowly lobed extension to 0.3 mm long at tip, glabrous, longitudinally dehiscent; pollen light yellow, copious, dry, wind–borne; pistil absent.
Pistillate inflorescence spike, terminal at tip of new shoot, mostly 2—3–flowered, erect; peduncle < 7 mm long, with several vegetative shoots arising at base, short–tomentose and glandular–pubescent; bract subtending “flower” absent; involucre containing female flower, ovoid, ca. 6 × 3 mm, formed by fusion of 1 bract and 2 bracteoles into a single uniform structure fused to and surrounding 3/4 to 7/8 of ovary, covered with tufted, branched hairs and glandular–pubescent.
Pistillate flower perianth (calyx) ca. 5–lobed; tube fused with involucre and ovary wall, constricted at tip; lobes erect to ascending, unequal, triangular, 1.2—1.9 × 1—1.3 mm long, green, sometimes with several much smaller lobes interior to calyx lobes narrowly triangular and < 0.8 mm long; stamens absent; pistil 1, within involucre; ovary inferior, subspheroid, green, 2–chambered, each chamber with 1 ovule; styles 1, 2–branched, lower portion stout, ca. 1.5 × 1.5 × 1.2 mm, the branches spreading, fusiform ca. 8 × 3 mm, stigmatic for most of length in ± longitudinal, bumpy, feathery (plumose) crests, green aging rose–colored.
Fruit drupelike nut, 1—2 per cluster, indehiscent, 1—2–seeded, spheric, while attached to plant in range 36—42 mm, dull green, when shed becoming purplish brown and low–dimpled; husk leathery, strongly aromatic, with dried glandular hairs; pulp blackening fingers when handled and turning black (tannins), easily cut; nut shell (endocarp) spheroid in outline and woody, ca. 25 mm across, extremely hard, shallowly grooved with rough to warty surfaces between grooves.
A. C. Gibson