A new species of Psilophyton from the Lower Devonian of northern New Brunswick, Canada

Publisher Website
Google Scholar
Abstract
A new spiny trimerophyte is described from early to middle Emsian (Lower Devonian) strata of Atholville, New Brunswick, Canada, where the specimens occur in a secondarily silicified tuff. P. crenulatum sp. nov. is characterized by vegetative branches which are 2 mm to 8.3 cm long, 2-7 times dichotomous and terminated by slender recurved tips. Some vegetative divisions are 2 closely spaced dichotomies (double dichotomies) which appear as trifurcations. The central axis of the trifurcation varies from about 1 mm to 2.5 cm in length. Fertile units terminate a dichotomous axis, and are alternate and distichous or are helically arranged. They are 5-7 times dichotomous in 3 dimensions and consistently pendulous after the 2nd or 3rd dichotomy. These units are covered with crenulations on the 1st few orders of branching and terminate in sporangia 3-5 mm long by 1-2 mm wide. Sporangia are consistently twisted around each other. In situ spores are 48-102 .mu.m in diameter and are compared with the dispersed spore genus Apiculiretusispora. Stomata are reported but an epidermis is usually lacking in most specimens. Spines are terete in cross section, multicellular, up to 6 mm long, and undivided, bifurcate or trifurcate. Crenulations are semicircular to oval and 100-200 .mu.m in diameter. Vascular strands up to 1 mm in diameter are centrarch with metaxylem tracheids that have scalariform- to circular-bordered pits. P. crenulatum represents the oldest known bonafide species of Psilophyton. A reconstruction is included along with a discussion on the evolution of megaphyllous leaves, the origin of adventitious roots, and branching similarities between P. crenulatum and younger ferns.

This publication has 5 references indexed in Scilit: