Comments: Placed in the genus Scaphiopus by some authors. Hall (1998) argued against the recognition of SPEA as a distinct genus, but most authors have accepted the split of SPEA from Scaphiopus.
Wiens and Titus (1991) presented a phylogenetic analysis of the genus (or subgenus) SPEA based on allozymic and morphological data.
Regarded as conspecific with S. HAMMONDII until 1976 (Brown 1976); retained within HAMMONDII by some authors (Tanner 1989), but various data support the contention that these are distinct species. In Tanner (1989), the name MULTIPLICATUS (as a subspecies) is associated with populations in the mountains and plateaus of Chihuahua and Durango; southwestern U.S. populations that recently have been referred to as S. MULTIPLICATA are called S. HAMMONDII STAGNALIS (hence Scaphiopus [or SPEA] STAGNALIS if regarded as a species distinct from populations of HAMMONDII in California and Baja California). Sometimes hybridizes with Bombifrons (Sattler 1985).
Garcia-Paris et al. (2003) used mtDNA to examine the phylogentic relationships of Pelobatoidea and found that the family Pelobatidae, as previously defined, is not monophyletic (Pelobates is sister to Megophryidae, not to Spea/Scaphiopus). They split the Pelobatidae into two families: Eurasian spadefoot toads (Pelobates), which retain the name Pelobatidae, and North American spadefoot toads (Scaphiopus, Spea), which make up the revived family Scaphiopodidae.