Another Successful Establishment of Pawpaw (Asimina triloba, Annonaceae) in Massachusetts

In 2019, the first naturalized population of pawpaw, Asimina triloba (L.) Dunal, in Massachusetts was found by Barbara Katzenberg (Standley and Katzenberg 2019) in Lexington, Massachusetts. In October 2020, Russ Cohen located a second population approximately 1.5 km west of the original, in the Town of Lexington’s Parker Meadow Conservation Area. This population extends across almost 0.8 ha, with stem densities reaching 30 per square meter. Numerous trees are 8 to 10 cm in diameter and 6 to 7 m tall. Ripening fruits were present on the larger trees and on the ground. There are several disjunct clusters of stems, separated by up to 15 m of woods and trails. These discrete clusters are likely to represent separate clones resulting from independent seedling establishment. Plants were observed in undisturbed woods, open wet woods, and on a linear dredge spoil pile. The character of this newly discovered naturalized pawpaw patch, in terms of the size, density, and distribution of the plants present, growing underneath a canopy of taller trees, compares very favorably to naturally occurring populations of this species Cohen has observed in its native range further south (e.g., the Ohio River Valley). The origin of this naturalized population more than 200 miles from the natural range limit in western New York and northern Pennsylvania (Kral 1997) is unknown, likely human-mediated seed or seedling establishment from a cultivated source. Pawpaw has been cultivated at the Arnold Arboretum since 1880 (Arnold Arboretum 2021) and is known to us to be cultivated at other locations in Middlesex County. The presence of multiple clones of different ages at this location suggests successful sexual reproduction and short-distance seed dispersal by natural agents, perhaps coyotes, as documented by Cypher and Cypher (1999). The extensive spread and apparent recruitment from seed of pawpaw at this suburban Boston location suggests that increasingly temperate conditions brought on by climate change are favorable to vegetative and sexual reproduction of more southerly species such as Asimina triloba and allow them to occupy New England habitats, including natural woodlands (see also Bellemare and Deeg 2015). Using bioclimatic modelling,