Affected by a virus (?) and producing abnormal narrow leaves. This condition is well known and has been employed for developing
a horticultural variety (a cultivar). See Flora of North America: "Two horticultural forms of Frangula alnus are widely sold and planted in North America. The cultivar 'Asplenifolia' (Frangula alnus var. asplenifolia Dippel; fernleaf or cutleaf buckthorn) has linear-oblong leaves with coarsely toothed to incised margins and commonly is
grown as a specialty plant. The cultivar 'Columnaris' (tallhedge glossy buckthorn) has a narrow, upright habit and is used
in hedging. Both forms were noted by M. H. Brand (http://www.hort.uconn.edu/plants/r/rhafra/rhafra1.html) to spread invasively
by seeds. 'Asplenifolia' has been reported as naturalized in Ontario (A. W. Dugal 1989, 1992), Illinois (A. Branhagen, pers.
comm.), and Ohio (M. K. Delong et al. 2005)." Apparently, Massachusetts is not an exception.