ESSEX   BOTANY   AND   MYCOLOGY  GROUPS 

Native. This a distinctive deciduous fern, with long, dull green mealy petioles giving rise to three bipinnate segments that form the thin, dull, grey-green minutely gland-covered lamina, the two lateral segments being only half the size of the terminal segment so that the overall tripartite lamina is narrowly-triangular. The segments are unfurled early in the spring from a single ball-shaped primordium in the young leaf, in contrast to the separate three-balled arrangement in G. dryopteris. The sori are orbicular, naked, and arranged near the margin on the underside of the pinnules. The fronds arise singly quite a distance apart from a long, branched, creeping rhizome. They die back with the first frosts. G. dryopteris differs from it in having a much more delicate petiole, and in having the three blade segments more of less equal in size and lacking the glandular petiole and lamina. It is typically a fern of calcium rich substrates, on broken ground, ledges and cliffs on a variety of limestone subtrates, and prefers the more southern sunnier and drier climates than Oak Fern. Elsewhere, like Oak Fern it turns up occasionally on damp walls, particularly on railway bridges, where the steam from trains probably kept it moist. There have been odd records from Norfolk, Suffolk, and Hertfordshire and just one, on a limestone wall, from Essex. Possibly originally introduced with the limestone blocks of the wall