PSARONIUS

genus of fossil ferns that resembled modern tree ferns. It is included in the division (or class) Pterophyta. The plants had long doubly divided fronds arranged in a complex pattern of helices crowning the trunk. The trunk was peculiar in that it had a central stem surrounded for almost its entire length by a compact layer of roots; it tapered strongly from a wide basal stump to a bare stem high up the column, almost 7 1/2 metres (25 feet) tall.