Specimens have been found in northern Maine, USA; Gaspé Bay, Quebec and New Brunswick, Canada; the Czech Republic; and Yunnan, China.

Plants lacked leaves or true roots; spore-forming organs or sporangia were borne on the ends of branched clusters.

One exception is P. krauselii, from the Czech Republic, which is younger, being from the upper part of the Middle Devonian (around 390 to 380 million years ago).

The conducting elements of the xylem, the tracheids, were of the so-called 'P-type' in which the walls were strengthened by ladder-like (scalariform) bars with circular openings between them.

[16] Compared to P. dawsonii, both P. princeps and P. forbesii had a greater distinction between main stems and side branches, which may be considered an 'advanced' feature.

It appears to have been considerably smaller than the previous species, perhaps 30 cm tall, with smooth dichotomously branching stems, and sporangia only 2 mm long.

[16] Kasper et al. suggested that the smaller species P. dapsile and P. krauselii, which had mainly dichotomous branches, were the more 'primitive' members of the genus.

[15] P. primitivum was found in Yunnan, China, in the Posongchong Formation, which is of Pragian (Siegenian) age (around 410 million years ago).

[13] Leafless, dichotomously branching fossils bearing spines and possessing vascular tissue from the Devonian of Gaspé Peninsula, Canada, were thought by Dawson in 1859 to resemble the modern whiskfern, Psilotum.

Unfortunately, it later turned out that his description and subsequent reconstruction was based on fragments of three different unrelated plants, which caused confusion for many years.

[18] At first most of the early polysporangiophytes (land plants other than liverworts, mosses and hornworts) were placed in a single class, Psilophyta, established in 1917 by Kidston and Lang.

[20] The distinction between main stems and strongly branched lateral stems evident in species such as P. forbesii has been considered to be one of the key steps towards the evolution of the leaves of euphyllophytes (modern members of which are the ferns and seed plants), based on the theory that such leaves evolved through 'webbing' of flattened lateral branching systems.