2. Celtis occidentalis L. (northern hackberry, nettle tree)

C. occidentalis var. canina (Raf.) Sarg.

Pl. 569 p; Map 2660

Plants medium to large trees 10–35 m tall (rarely shrublike and shorter at dry sites), typically with one strong, vertical trunk (occasionally with 2 or 3 parallel, strongly ascending trunks). Bark of trunk and large branches with prominent corky ridges and/or warts. Twigs glabrous (rarely sparsely pubescent with stiff, spreading hairs, especially on juvenile plants), the winter buds 1.5–5.0 mm, ovoid or flattened, bluntly pointed at the tip, orange-brown or purple, glabrous or minutely hairy. Leaves thin and flexible when dry, both surfaces the similarly bright green or the undersurface somewhat paler, the upper surface plane or weakly grooved over the midvein and secondary veins (sometimes also over some of the minor veins), the undersurface with sparse hairs along the main veins and often also with dense tufts of hairs in the vein axils, or sometimes the blade totally glabrous, the margins plane or narrowly curved under. Leaves subtending fruits with the petiole 9–15 mm long, glabrous or the upper surface sparsely hairy; the blade 7–12 cm long, 4.0–7.7 cm wide, obliquely triangular-ovate, very obliquely truncate or sometimes slightly asymmetrically rounded at the base; gradually tapered to a slender, sharply pointed tip, the margins relatively evenly toothed with 12–27 teeth on the shorter side and 23–40 teeth on the longer side; the upper surface smooth or slightly roughened, the secondary veins 5–8 on each side, the basal secondary veins extending to 1/3–2/5 of blade length (occasionally to 1/2 the blade length on one side). Leaves of vigorous leading shoots 8.5–18.0 × 3–11 cm, narrowly triangular to triangular-ovate, evenly toothed for their whole length; leaves of juvenile plants triangular-ovate, the base sometimes symmetric, the margins sharply toothed, the tip gradually long-tapered, the upper surface smooth or roughened. Flower stalks 12–24 mm long, 1.2–2.2 times as long as the subtending petiole, glabrous. Stamens with the anthers always dehiscent, the pollen copious and well-formed (95–100% stainable with acetocarmine). Fruits more or less spherical, 8–10 mm long, dark brownish purple when fully mature. 2n=20. March–April.

Scattered nearly throughout the state, but uncommon to absent from the western portion of the Glaciated Plains Division (eastern U.S. west to Montana and New Mexico; Canada). Bottomland forests, mesic upland forests, banks of streams, rivers, and spring branches, margins of sinkhole ponds, bases of bluffs, and occasionally edges of upland prairies and glades, and tops of bluffs; also old fields, cemeteries, and roadsides.

Celtis occidentalis is distinctive in having larger leaf blades that are evenly toothed for their whole length, with more numerous secondary veins that are more nearly parallel so the areoles are long and narrow, whereas our other species have areoles that are wider relative to their length; the areoles often are widest near the midvein and gradually narrowed for their whole length, but venation is variable. Leaves that subtend fruit in C. occidentalis are gradually tapered for at least half of their length. The bark of C. occidentalis often shows much heavier development of corky warts and ridges than in other Missouri species, but this character is very variable.

For further discussion on the differences between this species and C. pumila, see the treatment of that species.