Comments: This species was removed from genus Trionyx and placed in genus Apalone by Meylan (1987). North American softshell turtles were retained in Trionyx by Webb (1990) and Ernst et al. (1994). Subsequently, most authorities have accepted Apalone as the generic name for North American softshell turtles
Molecular data indicate a genetic dichotomy between populations north and west of Louisiana (exclusive of basal Rio Grande drainage populations) and populations from the Gulf Coast in southeastern North America (Weisrock and Janzen 2000).
McGaugh et al. (2008) examined the deep lineage divide (based on mtDNA data) between southeastern + northern subspecies (A. s. aspera + A. s. hartwegi + A. s. spinifera) and western subspecies (A. s. pallida + A. s. emoryi + A. s. guadalupensis) with broader sampling and using mitochondrial and nuclear markers. The southeastern + northern clade and the western clade maintained mitochondrial reciprocal monophyly, but nuclear loci showed no phylogenetic resolution and suggested that taxonomic elevation of the two mitochondrial clades would be currently unjustified. Genetic data did not support the subspecific distinction between A. s. spinifera and A. s. hartwegi; McGaugh et al. (2008) suggested that the two taxa be lumped (as A. s. spinifera).
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