Common Pawpaw

Appearance

"A. triloba" is a large shrub or small tree growing to a height of 35 ft, rarely as tall as 45 ft, with trunks 8–12 in or more in diameter. The large leaves of pawpaw trees are clustered symmetrically at the ends of the branches, giving a distinctive imbricated appearance to the tree's foliage.

The leaves of the species are simple, alternate and spirally arranged, entire, deciduous, obovate-lanceolate, 10–12 in long, 4–5 in broad, and wedge-shaped at the base, with an acute apex and an entire margin, with the midrib and primary veins prominent. The petioles are short and stout, with a prominent adaxial groove. Stipules are lacking.

The expanding leaves are conduplicate, green, covered with rusty tomentum beneath, and hairy above; when fully grown they are smooth, dark green above, and paler beneath. When bruised, the leaves have a disagreeable odor similar to a green bell pepper. In autumn, the leaves are a rusty yellow, allowing pawpaw groves to be spotted from a long distance.

Pawpaw flowers are perfect, about 1–2 in across, rich red-purple or maroon when mature, with three sepals and six petals. They are borne singly on stout, hairy, axillary peduncles. The flowers are produced in early spring at the same time as or slightly before the new leaves appear, and have a faint fetid or yeasty smell.

The fruit of the pawpaw is a large, yellowish-green to brown berry, 2–6 in long and 1–3 in broad, weighing from 0.7–18 oz, containing several brown or black seeds 1⁄2–1 in in diameter embedded in the soft, edible fruit pulp. The conspicuous fruits begin developing after the plants flower; they are initially green, maturing by September or October to yellow or brown. When mature, the heavy fruits bend the weak branches down.

Naming

The common name of this species is variously spelled pawpaw, paw paw, paw-paw, and papaw. It probably derives from the Spanish "papaya", an American tropical and subtropical fruit sometimes also called "papaw", perhaps because of the superficial similarity of their fruits and the fact that both have very large leaves.

Distribution

The pawpaw is native to the Eastern, Southern, and Midwestern United States and adjacent Ontario, Canada, from New York west to southeastern Nebraska, and south to northern Florida and eastern Texas.

Habitat

The tree commonly grows in floodplains and shady, rich bottomlands, where it often forms a dense, clonally spreading undergrowth in the forest, often appearing as a patch or thicket of individual, small, slender trees. Pawpaws are not the first to colonize a disturbed site, but may become dominant and slow the establishment of oaks and hickories. Although shade-tolerant, pawpaws do not persist in undisturbed old growth forest.

Reproduction

Pawpaws spread locally primarily by root suckers; sexual reproduction by seed does also occur, but at a fairly low rate.

Pawpaw flowers are insect-pollinated, but fruit production is sometimes limited as few if any pollinators are attracted to the flower's faint, or sometimes nonexistent scent. The flowers produce an odor similar to that of rotting meat to attract blowflies or carrion beetles for cross-pollination. Other insects that are attracted to pawpaw flowers include scavenging fruit flies, carrion flies, and beetles. Because of irregular fruit production, some believe pawpaw plants are self-incompatible, requiring cross-pollination between trees of different clones.

Food

Larvae of the zebra swallowtail, a butterfly, feed exclusively on young leaves of "A. triloba" and various other pawpaw species, but never occur in great numbers on the plants.

Chemicals in the pawpaw leaves confer protection from predation throughout the butterflies' lives, as trace amounts of acetogenins remain present, making them unpalatable to birds and other predators.Pawpaws are sometimes included in ecological restoration plantings, since this tree grows well in wet soil and has a strong tendency to form well-rooted colonial thickets.

Evolution

The natural distribution of the common pawpaw in North America, prior to the ice ages and lasting until roughly 10,000 years ago, was done by certain megafauna until they became extinct during the Quaternary extinction event. After the arrival of humans and the subsequent extinction of megafauna that were distributing "A. triloba", the probable distribution of these large fruit-bearing plants has been by humans.