Hobby identification at the Phormictopus species level is challenging. The genus comprises the largest tarantulas of the Caribbean. Interestingly, few if any Phormictopus species have ever been found in surrounding continental North and South America, home to other large tarantulas in the Aphonopelma, Brachypelma, Sericopelma, Theraphosa, Pamphobeteus, and Xenesthis genera.
Maria Gombasne Gudenus et al have tackled Phormictopus taxonomy at an advanced hobbyist level. In July 2016 they published their findings in the Journal of the BTS (pdf). They begin by distinguishing Cuban from non-Cuban Phormictopus:
“These two groups have a clear separation with regards to visible attributes related to colour, size and habitus (body build). The offspring of the two groups also have different colours. While Cuban species have brownish young, those found outside Cuba are bluish.”
The most well-known Cuban Phormictopus species is Phormictopus auratus. Outside of Cuba it is Phormictopus cancerides (Hispaniola). In the past several years, Hispaniola (Haiti and the Dominican Republic) has yielded a number of lineages with varying shades of brown, purple, green, and blue. Spermathecae examination by the Gudenuses suggests species differences between various groups as well as between these groups and P. canderides.