The Royal Fern

Fertile Frond of the Royal Fern, Osmunda regalis

Some ferns are quite similar. The small filmy ferns Wilson's Filmy Fern (Hymedophyllum wilsonii) and Tunbridge Filmy Fern (H. tunbrigense) are virtually identical at first glance, with subtle features like the presence or absence of toothed edges on the scales protecting the sori having to be examined to differentiate them. One fern that doesn't have that problem though is the Royal Fern, Osmunda regalis. A strikingly distinctive fern, found in wet bogs and fens throughout Ireland (with a global distribution spanning Europe, Asia and Africa) its fronds can reach heights of 160 cm (1). Most of these are sterile, with the fertile fronds rising above the others in the centre of the plant. Their shuttlecock-like appearance and the fern's overall imposing height are unmistakable.

The Royal Fern, Osmunda regalis

Or are they? Homosporous ferns have two free-living generations, the sporophyte generation which is what most people would call the fern, and the relatively short lived gametophyte generation. The gametophyte generation is much smaller and shows far less morphological complexity. This means that identification is often next to impossible. Identification of fern gametophytes is important as they play an important part in fern dispersal and ecology. This problem has been overcome by the use of DNA-based identification. A sample of a gametophye in cultivation that was unknown for 30 years was identified as O. regalis using plastid sequencing (2). The gameteophyte never produced antheridia, and so never produced the sporophyte stage, and morphological analysis was inconclusive. Its identification as O. regalis shows the power of DNA-based techniques in revealing more about the ecology of fern gametophytes.

References:

1. Phillips, 1980. Grasses, Ferns, Mosses and Lichens of Great Britain and Ireland p. 105
2. Schneider and Schuettpelz, 2006. Molecular Ecology Notes 6 pp. 989-991