Woodsia

 Brittle bladder fern Cystopteris fragilis, photographed by Carl Farmer.

Belongs within: Polypodiales.

The Woodsiaceae is a cosmopolitan family of mostly terrestrial ferns. The circumscription of this family has been somewhat contentious in the past in relation to other possible families such as Athyriaceae. The cliff ferns of the genus Woodsia are found in northern temperate regions.

Cliff ferns
Published 15 June 2019

Historically, the higher classification of ferns has tended to be a bit wobbly. Compared to flowering plants, ferns often offer fewer readily observable features that may offer clues to relationships. As a result, the position of many fern taxa has long been uncertain. One such group is the cliff ferns of the genus Woodsia.

Woodsia scopulina, copyright Jim Morefield.

Cliff ferns, as their name suggests, are commonly found growing on rocks. There are a few dozen species, mostly found in cooler regions of the Northern Hemisphere. A single species, Woodsia montevidensis, extends into South America and southern Africa (Rothfels et al. 2012). They have short creeping rhizomes with a covering of scales and leaves bearing a mixture of scales and hairs. The most distinctive feature of the cliff ferns can only be seen on fertile fronds: the sori (spore packets) are covered by an indusium that is attached to the leaf basally relative to the sori. These indusia are commonly composed of an array of scales or filamentous sections, in contrast to the solid indusia of other ferns.

Underside of pinnule of Woodsia plummerae, showing the filamentous indusia, from here.

Historically, Woodsia has been placed in a family Woodsia with a number of superficially similar fern genera such as the bladder ferns of the genus Cystopteris. However, molecular phylogenetic analyses have disputed the monophyly of such a group. Rothfels et al. (2012) divided the ‘woodsioid’ ferns between no less than six different families with Woodsiaceae in the strict sense limited to the cliff ferns alone. Though some authors have divided the cliff ferns between multiple genera, an analysis of the group by Shao et al. (2015) found it difficult to reliably distinguish such subgroups and recommended recognition of only a single genus. They did, however, recognise three major clades within Woodsia identified by molecular phylogenetic analysis as distinct subgenera. The type subgenus Woodsia is distinctive among ferns in possessing articulated stems; species of this subgenus are widespread in the Palaearctic region. The subgenus Physematium is mostly found in the Americas and is characterised by bicolored scales on the rhizome. The third subgenus, Cheilanthopsis, is found in eastern Asia with the centre of diversity in the Himalayan region. The rhizome scales are concolorous, and the indusia are solid and globose rather than being composed of individual segments. In some cases in this subgenus, the sori are covered by ‘false indusia’, indusium-like structures that are formed from inrolled leaf margins rather than being independent membranes.

Systematics of Woodsia
<==Woodsia [incl. Hymenocystis, Protowoodsia; Woodsiaceae]RS12
    |--W. alpinaRS12
    |--W. andersonii (Bedd.) Christ 1905 [=Gymnogramma andersonii Bedd. 1868; incl. W. hyperborea Brown 1810]I88
    |--W. cycloloba Hand.-Mzt. 1929I88
    |--W. elongata Hooker 1844 [=Cheilanthopsis elongata (Hooker) Copel. 1931]I88
    |--W. glabellaRS12
    |--W. ilvensisRS12
    |--W. manchuriensisRS12
    |--W. mollisL54
    |--W. montevidensisJ87
    |--W. okamotoiCP02
    |--W. oreganaH93
    |--W. plummeraeH93
    |--W. polystichoidesSS04
    `--W. scopulinaH93

*Type species of generic name indicated

References

[CP02] Chung, S.-W., & C.-I. Peng. 2002. Senecio kuanshanensis (Asteraceae), a new species from southern Taiwan. Botanical Bulletin of Academia Sinica 43: 155–159.

[H93] Hickman, J. C. (ed.) 1993. The Jepson Manual: Higher Plants of California. University of California Press: Berkeley (California).

[I88] Iwatsuki, K. 1988. An enumeration of the pteridophytes of Nepal. In: Ohba, H., & S. B. Malla (eds) The Himalayan Plants vol. 1. The University Museum, University of Tokyo, Bulletin 31: 231–339.

[J87] Judd, W. S. 1987. Floristic study of Morne La Visite and Pic Macaya National Parks, Haiti. Bulletin of the Florida State MuseumBiological Sciences 32 (1): 1–136.

[L54] Lötschert, W. 1954. Beitrag zur Pteridophyten-Flora von Mittel-Amerika. Senckenbergiana Biologica 35 (1-2): 109–119.

[RS12] Rothfels, C. J., M. A. Sundue, L.-Y. Kuo, A. Larsson, M. Kato, E. Schuettpelz & K. M. Pryer. 2012. A revised family-level classification for eupolypod II ferns (Polypodiidae: Polypodiales). Taxon 61 (3): 515–533.

[SS04] Schneider, H., E. Schuettpelz, K. M. Pryer, R. Cranfill, S. Magallón & R. Lupia. 2004. Ferns diversified in the shadow of angiosperms. Nature 428: 553–557.

Shao, Y., R. Wei, X. Zhang & Q. Xiang. 2015. Molecular phylogeny of the cliff ferns (Woodsiaceae: Polypodiales) with a proposed infrageneric classification. PLoS One 10 (9): e0136318.

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