1. Asimina triloba (L.) Dunal (pawpaw)

Pl. 202 g–i; Map 837

Plants small trees, rarely to 10 m tall, often forming colonies from root suckers. Bark thin, smooth, becoming roughened (warty) or rarely scaly on older trees, gray or less commonly dark brown, usually with white to light gray patches. Twigs light to dark reddish brown, glabrous or sparsely hairy, the buds lacking scales, reddish brown, hairy, the terminal bud flattened and narrowly ovate in outline, the lateral buds nearly globose. Leaves alternate, simple, 10–35 cm long, oblanceolate to oblong-obovate, gradually narrowed or tapered to a petiole 5–20 mm long at the base, abruptly tapered to a short point at the tip, glabrous at maturity (hairy when very young), the veins prominent, the margins entire, the upper surface green and usually shiny, the undersurface pale green. Stipules absent. Flowers produced before or as the leaves develop, solitary at the nodes of the leafless second year’s growth along branches, perfect, hypogynous, with short, hairy stalks. Sepals 3, 8–12 mm long, broadly triangular, sharply pointed at the tip, green, usually hairy, and shed early. Petals in two unequal and strongly overlapping series of 3, the outer series 2.1–2.7 cm long, broadly ovate, the tips spreading and curled outward, the inner series 1.0–1.4 cm long, ovate, erect or with the tips somewhat spreading, the surface of both series with prominent veins, dark purplish brown to maroon at maturity (often green during development), hairy on the outer (under) surface, the inner series with nectar-producing glands at the base of the inner surface. Stamens numerous, small, free, densely packed around the elongated receptacle, not clearly differentiated into an anther and filament. Pistils 3–5(–15), hairy, with 1 carpel, the ovary superior and with 12–16 ovules, the style short, the stigma globose. Fruits single or 2–4 in a spreading or drooping cluster, berries, 4–13 cm long, ellipsoid to more or less cylindrical, rounded at the ends, pale green, turning yellowish and then brownish black with age. Seeds 2–10, 2.0–2.8 cm long, flattened, elliptic-ovate in outline, dark brown, shiny, embedded in a white to light yellow pulp. 2n=18. March–May.

Scattered to common nearly throughout the state (eastern U.S. and adjacent Canada west to Nebraska and Texas). Bottomland forests, mesic upland forests in ravines, banks of streams and rivers, and bases of bluffs.

Plants of Asimina are aromatic. The leaves have an odor similar to that of motor oil when bruised. The flowers have an aroma similar to fermenting grapes. The bruised or opened fruits also have a perfumy aroma. The fruits of pawpaws have been called Indiana bananas and Missouri bananas and are considered a delicacy by wild foods enthusiasts, although others may find the taste nauseating. If not already eaten by birds or mammals, they may be harvested in September and early October, when they are slightly soft to the touch. The pulp has a creamy texture and a strong, sweet, exotic flavor. It may be eaten raw or made into ice cream, sherbet, pudding, pie, jelly, or other confections. Care must be taken, as some individuals develop dermatitis when handling the fruits or have an allergic reaction to the ingested pulp. The seeds are poisonous. Aside from the fruits, most other parts of the plant (especially the bark) contain a variety of poisonous chemicals, including alkaloids (such as asiminine and analobine) and a group of fatty acid lactones called acetogins (notably asimicin). The acetogins of pawpaw are under investigation as potential anticancer and antitumor drugs, and also for possible applications as pesticides. Other uses of pawpaw include cultivation as a small shade tree (especially the cultivars with thicker trunks and reduced suckering). Pioneers and some Native Americans used strips of the tough, thin bark for weaving into cloth and for fish stringers.

The leaves of Asimina are a principal larval food source for the zebra swallowtail butterfly (Euritides marcellus Cramer). Although most members of the Annonaceae are pollinated by beetles, it is possible that A. triloba is pollinated by flies. Robertson (1889) reported visitation of flowers on Illinois plants by several different small flies, and Joe Smentowski (personal communication) of Brentwood, Missouri, reported seeing small, nocturnal flies attracted by the odor of the flowers.