Asimina triloba (L.) Dunal


Asimina triloba plant

Family - Annonaceae

Habit - Small trees, usually strongly colonial from root suckers.

Stems - To 10 m. Bark gray, usually with white to light gray patches, thin, smooth, becoming roughened (warty) or rarely scaly on older trees. 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.

Asimina triloba barkBark of medium-aged tree.

Asimina triloba twigWinter twig.

Leaves - Alternate, simple, petiolate. Petiole 5-20 mm long. Stipules absent. Blades 10-35 cm long, oblanceolate to oblong-obovate, narrowed or tapered 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.

Asimina triloba leaf

Asimina triloba budWinter bud.

Inflorescence - Flowers solitary at the nodes of the second year's growth along branches, produced before or as the leaves develop.

Flowers - Perfect, hypogynous, on short, hairy stalks. Sepals 3, 8-12 mm long, broadly triangular, sharply pointed, green, usually hairy, shed early. Petals in two unequal and strongly overlapping whorls 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, red-brown to maroon at maturity (green when immature), 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, hairy, with 1 carpel, the ovary superior and with 12-16 ovules, the style short, the stigma globose.

Asimina triloba sepalsSepals.

Asimina triloba flowersYoung flowers.

Asimina triloba flowerMature flower (from below).

Fruits - Berries, single or 2-4 in a spreading or drooping cluster, 4-13 cm long, ellipsoid to cylindrical, somewhat irregular, 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 light yellow edible pulp.

Asimina triloba fruitsFruit cluster.

Flowering - March - May.

Habitat - Understory tree in bottomland and mesic forests, along streams, ravines, base of bluffs.

Origin - Native to U.S.

Other info. - This common tree can be found throughout most of Missouri, and most of eastern half of the continental U.S. as well as Canada. The tree is recognized by its strongly colonial habit, smooth gray bark, and large leaves which are broadest above the midpoint.

Pawpaw trees produce an edible fruit, also known as a "custard apple," "Indiana banana," and numerous other regional appellations. The flesh is delicious raw or baked into cookies and breads, although some individuals find the flavor less than appealing, or even suffer allergic reactions. The trees must apparently out-pollinate for fertilization, and isolated (monoclonal) colonies of plants will often produce no fruit. Pollination may be dependent on flies such as carrion flies, and apocryphal stories abound regarding the effectiveness of hanging rotting meat near the trees to attract pollinators. Even under the best of conditions, fruit set is not high, and since the fruits are also prized by wildlife, they can be difficult to find at harvest time. A good harvesting method is to give trees a firm shake, dislodging ripe fruits (if any), which fall to the ground.

The pawpaw is an example of the "basal angiosperm," neither monocot nor eudicot but representing an earlier evolutionary stage. Like many species in this class, pawpaw has leaves which are aromatic due to presence of volatile secondary metabolites. The odor is variously described as resembling crankcase oil or roasted bell pepper. In addition to the aromatic oils, the plants contain an array of other structurally unusual and pharmacologically active compounds, including alkaloids and polyketides. Extracts have been used to formulate pesticides and shampoos effective against louse, flea, and tick infestations. Larvae of the zebra swallowtail butterfly are able to consume the leaves without ill effect, but the acetogenin compounds which subsequently wind up in the larval tissues confer a degree of protection from predation.

The bark of the tree can be woven into rope or made into clothing or fishing nets. Crushed seeds were used by settlers as an insecticide.

Photographs taken at the Kansas City Zoo, 5-1-00, in Brown Summit, NC., 3-23-03, and at Whetstone Conservation Area, Callaway County, MO., 2-25-04 (DETenaglia); also at Glassberg Conservation Area, Jefferson County, MO, 5-9-2013, and along the Meramec River near Glencoe, St. Louis County, MO, 7-17-2017 (SRTurner).