AILANTHUS ALTISSIMA (Miller) Swingle. Ailanthus or Tree of Heaven. (× 1/2.)
ACERÀCEAE. The Maple Family.
Trees with terete branches; scaly buds; long petioled, opposite leaves; fruit consists of two long-winged samaras which are joined at their base, separating at maturity. The sap of some of the species, when concentrated, yields the maple sugar and sirup of commerce.
| Leaves trifoliate or pinnate | [1 A. Negundo.] |
| Leaves simple. | |
| Winter buds blunt; flowers appear from lateral buds before the leaves; fruit maturing in the spring or early summer. | |
| Leaves entirely glabrous beneath at maturity, 5-lobed; the two sinuses between the three largest lobes generally somewhat closed, formed as it were by the arcs of two circles which meet to form the sinus, and which if they were extended outward would cross each other within a few dm. of the sinus; fruit more or less pubescent at maturity | [2 A. saccharinum.] |
| Leaves are never all entirely glabrous at maturity, 3-5 lobed; the two largest sinuses are generally angular with straight sides which if extended outward would never cross; fruit smooth at maturity. | |
| Twigs smooth at maturity; leaves at maturity smooth beneath except a few hairs in the axils of the veins, or more rarely the entire lower surface covered more or less with a short pubescence; mature fruit generally 2-3.5 cm. long | [3 A. rubrum.] |
| Twigs more or less pubescent at maturity; leaves beneath covered with a dense tomentum which remains until maturity or sometimes becoming scanty; fruit about 4-5 cm. long | [A. rubrum var. Drummondii.] |
| Winter buds acute, sometimes somewhat blunt; flowers appear from terminal buds after the leaves; fruit maturing in the autumn. | |
| Leaves yellow green beneath; base of the petiole of the terminal leaves enlarged at the base, smooth or somewhat pubescent about the enlarged base | [4 A. nigrum.] |
| Leaves not yellow green beneath; base of the petiole of the terminal leaves not enlarged, petioles smooth, or if pubescent at the base the pubescence will be more or less evident the entire length of the petiole. | |
| Petioles smooth; leaves 3-5 lobed, blade as long or longer than wide, not densely pubescent beneath at maturity | [5 A. saccharum.] |
| Petioles smooth; leaves 3-lobed, blades wider than long | [A. saccharum var. Rugelii.] |
| Petioles pubescent, rarely smooth; leaves 5-lobed, rarely 3-lobed, the under surface densely pubescent at maturity | [A. saccharum var. Schneckii.] |