to Asimina by Gray in 1886. Small (1933) split it into 2 separate genera, Asimina and Pityothamnus, and in 1939 Fries merged them again into the one genus, Asimina.
Asimina is the only genus of the Annonaceae native to the temperate zone, with A. triloba being the hardiest species, growing as far north as the Great Lakes of North America (southern Michigan and southern Ontario). In earlier geologic times Asimina was more widely distributed than today; fossil leaves (Asimina eocenica Lesq.) have been recovered in Texas, Colorado, and Wyoming from the Eocene (Lamotte, 1952). In 1960, Kral published the most complete treatment of the genus, based upon extensive field work and thorough examination of herbarium specimens. He recognizes eight species as comprising Asimina: A. triloba, A. parviflora (Michx.) Dunal, A. obovata (Willd.) Nash, A. incana, A. reticulata Shuttlew. ex Chapman, A. longifolia Kral, A. pygmaea (Bartr.) Dunal, and A. tetramera Small. These eight have affinities that subdivide Asimina into essentially 2 groups, the northern pawpaws and the Florida dwarf pawpaws.
Asimina triloba is the common northern pawpaw, a small tree, to 11 m tall. It is the hardiest of the 8 species, to zone 5 (-25°C). Adapted to a humid continental climate, it requires a minimum of 400 annual chill units (based on Swartz and Gray, 1982), a minimum of 160 frost-free days or 1450 total growing degree days (calculated to a 10°C base with a 30°C maximum), and a minimum of 80 cm of precipitation annually with the majority during the spring and summer. It prefers rich, moist, well-drained soils. This is the most common and wide-spread species. Its range covers most of eastern North America, principally the interior where it is a minor but frequent component of the deciduous forest; it is seldom found near the coast. Principal pollinators are flies and beetles (species unidentified). Principal dispersers are thought to be humans, raccoons, and opossums. It is not as plentiful as 200 years ago, because of the clearing of forests for agriculture. Although valuable germplasm may have been lost, the species is in no danger.
Asimina parviflora is the small-flowered pawpaw or dwarf pawpaw. It is a tall shrub, to 6 m tall, that closely resembles A. triloba, except that it is smaller in all its characteristics and is less hardy, to zone 7 (-15°C). It is adapted to an ocean moderated climate of the southeastern and southern Coastal Plain and inland through the piednont. It prefers rich moist soils but can also be found on dry uplands. Principal pollinators are probably beetles. Seed dispersers are believed to be turtles, raccoons, and opossums. As with A. triloba, A. parviflora is in little danger of being reduced by present human activity.
6 Kral (1960) proposes that the proper name for the woolly-leaved pawpaw is A. speciosa. I depart from Kral in this instance, by following Wilbur (1970) who argues that the earlier A. incana is correct. Wilbur also notes that the correct spelling, about which there has been some confusion, is incana not incarna.
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