1. Zanthoxylum americanum Mill. (common prickly ash, northern prickly
ash, toothache tree)
Pl. 552 h–j; Map
2566
Plants shrubs or
rarely small trees, colonial from rhizomes, dioecious, 0.5–3.0(–8.0) m tall.
Stems with usually few, ascending branches, the bark relatively smooth, gray to
dark brown with lighter blotches and scattered, small, light-colored, more or
less circular lenticels, occasionally becoming longitudinally fissured on old
trunks, armed with small, flattened, slightly downward-curved prickles, these
mostly subopposite and stipulelike at the nodes, the twigs gray to dark brown,
moderately to densely short-hairy when young, becoming glabrous with age.
Leaves alternate, short-petiolate, the petiole not jointed at the tip,
unwinged. Leaf blades pinnately compound with 5–11(–13) leaflets, these 1–6(–8)
cm long (progressively longer from the basal pair), oblong to elliptic, or
ovate, the lateral pairs sometimes very slightly oblique, angled or
short-tapered to a sessile or minutely stalked base, rounded or more commonly
angled to a bluntly or sharply pointed tip, the margins entire or minutely
scalloped, the upper surface dark green, sparsely to moderately and minutely
hairy along the veins, becoming glabrous with age, the undersurface pale green
to light green, moderately pubescent with somewhat longer, fine, somewhat
tangled hairs, mostly along the veins and near the margins, becoming nearly
glabrous with age. Inflorescences produced before the leaves, axillary, small
umbellate clusters, the individual flowers short-stalked (sometimes appearing
nearly sessile at flowering, the stalks elongating as the fruits develop).
Flowers imperfect. Sepals absent. Petals 4 or 5, 1.5–2.5 mm long, narrowly
oblong-obovate, overlapping in bud, yellowish green, with a minutely uneven
apical portion and usually a fringe of short, crinkly reddish brown hairs.
Stamens in staminate flowers 4 or 5 (absent or reduced to 4 or 5 minute
staminodes in pistillate flowers), alternating with the petals, the filaments
free, slender, and glabrous, attached outside of a small, often lobed or
incomplete nectar disc around the ovary base. Ovaries 2–5 per flower, each
short-stalked (reduced to a more or less lobed rudiment in staminate flowers),
glabrous, 1-locular with 2 ovules, rounded or short-tapered at the tip, the
styles fused above their bases, the stigma minute, with 2–5 lobes. Fruits 2–5
separate follicles per flower, each 4.5–6.0 mm long, ellipsoid to
ellipsoid-obovoid, tapered to a short stalk at the base, abruptly tapered to a
minute, oblique beak at the tip, the outer surface leathery, pitted, red to
dark red or reddish brown, sometimes brownish yellow with a reddish tinge,
glabrous or minutely hairy. Seeds 1 or 2 per fruit, 4.0–4.5 mm long, obovoid to
nearly globose, sometimes (in 2-seeded follicles) somewhat flattened, the outer
surface with faint, coarse facets or pits and finely pebbled, black, shiny. 2n=34.
April–May.
Scattered in the
state, most abundantly outside the Ozark Division (eastern U.S. west to North
Dakota and Oklahoma; Canada). Openings of mesic to dry upland forests, tops of
bluffs, savannas, glades, banks of streams and rivers, and margins of ponds,
lakes, and sinkhole ponds; also pastures, old fields, old strip mines, and
railroads.
Uphof (1922)
reported the closely related Z. clava-herculis L. (Hercules club,
southern prickly ash) from southeastern Missouri, but no herbarium specimens
have been located to substantiate his observations. This species occurs from
Virginia to Florida west to Oklahoma and Texas and differs in flowering after
the leaves expand and in having leaves with mostly 9–13 leaflets, the lateral ones
strongly oblique at their bases, more or less terminal, looser inflorescences,
and calyces of 5 sepals.