§ 1. RHUS proper. Fruit symmetrical, with the styles terminal.
[*] Flowers polygamous, in a terminal thyrsoid panicle; fruit globular, clothed with acid crimson hairs; stone smooth; leaves odd-pinnate. (Not poisonous.)—(§ Sumac, DC.)
1. R. týphina, L. (Staghorn Sumach.) Branches and stalks densely velvety-hairy; leaflets 11–31, pale beneath, oblong-lanceolate, pointed, serrate, rarely laciniate.—Hillsides. June.—Shrub or tree 10–30° high, with orange-colored wood. Apparently hybridizes with the next.
2. R. glàbra, L. (Smooth S.) Smooth, somewhat glaucous; leaflets 11–31, whitened beneath, lanceolate-oblong, pointed, serrate.—Rocky or barren soil. June, July.—Shrub 2–12° high. A var. has laciniate leaflets.
3. R. copallìna, L. (Dwarf S.) Branches and stalks downy; petioles wing-margined between the 9–21 oblong or ovate-lanceolate (often entire) leaflets, which are oblique or unequal at the base, smooth and shining above.—Rocky hills. July.—Shrub 1–7° high, with running roots.
[*][*] Flowers polygamous, in loose and slender axillary panicles; fruit globular, glabrous, whitish or dun-colored; the stone striate; leaves odd-pinnate or 3-foliolate, thin. (Poisonous.)—(§ Toxicodendron, DC.)
4. R. venenàta, DC. (Poison S. or Dogwood.) Smooth, or nearly so; leaflets 7–13, obovate-oblong, entire.—Swamps. June.—Shrub 6–18° high. The most poisonous species; also called Poison Elder.
5. R. Toxicodéndron, L. (Poison Ivy. Poison Oak.) Climbing by rootlets over rocks, etc., or ascending trees, or sometimes low and erect; leaflets 3, rhombic-ovate, mostly pointed, and rather downy beneath, variously notched, sinuate, or cut-lobed,—high-climbing plants (R. radìcans, L.) having usually more entire leaves.—Thickets, low grounds, etc. June.
[*][*][*] Flowers polygamo-diœcious, in small solitary or clustered spikes or heads which develop in spring before the leaves; leaves 3-foliolate; fruit as in first group. (Not poisonous).—(§ Lobadium, Torr. & Gray.)
6. R. Canadénsis, Marsh. Leaves soft-pubescent when young, becoming glabrate; leaflets rhombic-obovate or ovate, unequally cut-toothed, 1–3´ long, the terminal one cuneate at base and sometimes 3-cleft; flowers pale yellow. (R. aromatica, Ait.)—Dry rocky banks, W. Vt. to Minn., and southward.—A straggling bush, 3–7° high; the crushed leaves not unpleasantly scented.