and P. krauselii, which had mainly dichotomous branches, were the more 'primitive' members of the genus.

P. primitivum was found in Yunnan, China, in the Posongchong Formation, which is of Pragian (Siegenian) age (around ). All other species have been found in North America and Europe, which formed part of the continent of Laurussia in the Devonian. The name reflects a belief that the species is 'primitive', with considerable dichotomous