Kirk W. Pomper, Desmond R. Layne, and R. Neal Peterson
The pawpaw [Asimina triloba (L.) Dunal, Annonaceae] tree produces the largest edible tree fruit native to the United States (Darrow 1975; Layne 1996). This fruit, known commonly as the “poor man’s banana,” may reach up to 1 kg in size. Pawpaws grow wild in the mesic hardwood forests of 26 states in the eastern United States, ranging from northern Florida to southern Ontario (Canada) and as far west as eastern Nebraska (Kral 1960); as shown in Fig. 1. Pawpaws are hardy to USDA growing zone 5 (-15circF, -9.4circC) and flourish in the deep, rich fertile soils of river-bottom lands where they grow as understory trees or thicketshrubs (Sargent 1890). The unique qualities of the pawpaw fruit, ornamental value of the tree, and the natural compounds in the leaf, bark, and twig tissues that possess insecticidal and anti-cancer properties (McLaughlin 1997), suggest that pawpaw has great potential as an alternative high-value crop.
Pawpaw is the only temperate member of the tropical Custard Apple family (Bailey 1960), which includes several delicious tropical fruits such as the custard apple (Annona reticulata L.), cherimoya (A. cherimola Mill.), sweetsop or sugar apple (A. squamosa L.), atemoya (A. squamosa × A. cherimola), and soursop (A. muricata L.). There are also eight other members of the Asimina genus that are native to the extreme south-eastern states of Florida and Georgia. These include A. incarna (Bartr.) Exell. (flag pawpaw); A. longifolia Kral; A. obovata (Willd.) Nash; A. parviflora (Michx.) Dunal (dwarf pawpaw); A. pygmaea (Bartr.) Dunal; A. reticulata Shuttlw. ex Chapman; A. tetramera Small (opossum pawpaw); and A. × nashii Kral (Kral 1960).
Pawpaw is a small, deciduous tree that may attain 5 to 10 m in height and tends to be found in patches due to root suckering (Layne 1996). In sunny locations, trees typically assume a pyramidal habit, with a straight trunk and lush, dark green, long, drooping leaves (Fig. 2). The blossoms occur singly on the previous year's wood, reaching up to 5 cm in diameter, emerging before leaves in mid spring (about April in Kentucky). Flowers have a globular androecium and a gynoecium composed of 3–7 carpels or 3–7 fruited clusters (Kral 1960). Flowers are strongly protogynous, self-incompatible and require cross-pollination (Wilson and Schemske 1980), although some trees may be self-compatible. Pollination may be by flies (Wilson and Schemske 1980) and beetles (Kral 1960).
Fig. 1. Native range map of pawpaw (Asimina triloba).