Pteridaceae Ching

Pteridaceae are one of the largest fern families, comprising over 1000 species (~10% of extant ferns). But even more notable than their species richness is the remarkable morphological and ecological diversity of the family, which includes obligate epiphytes, free-floating aquatics, brackish-swamp dwellers, several clades specialized for colonizing rocky deserts, and many generalist understory species. While some of these life forms do appear in other fern lineages (many other families, for example, contain epiphytes), most are rare and no other fern family contains such a wide range of ecological specializations.

Pteridaceae have been the subject of much taxonomic disagreement—their members have been distributed among at least 20 different families: Acrostichaceae; Actiniopteridaceae; Adiantaceae; Anopteraceae; Antrophyaceae; Bommeriaceae; Ceratopteridaceae; Cheilanthaceae; Coniogrammaceae; Crytopgrammaceae; Hemionitidaceae; Llaveaceae; Negripteridaceae; Notholaenaceae; Parkeriaceae; Platyzomataceae; Pteridaceae; Sinopteridaceae; Taenitidaceae; and Vittariaceae (Smith et al. 1996; Hassler and Swale, 2003). Some of these former family designations (e.g., Llaveaceae, Parkeriaceae, and Vittariaceae) correspond to monophyletic groups now known to be nested within the broader Pteridaceae, while others (e.g., Taenitidaceae) are assemblages of more distantly related species (Schuettpelz et al., 2007).

Terrestrial, epilithic or (rarely) epiphytic ferns with a short life cycle or perennial. Rhizomes short or long, suberect, decumbent or creeping, often laterally branched; roots few or many, often fleshy. Stipe not articulated, often dark-coloured. Fronds tufted or widely spaced, mono- or dimorphic. Lamina pinnately compound, pedate, dichotomously forked or helicoid, often with a proliferating bud at the rhachis apex, herbaceous or coriaceous, glabrous or variously set with indumentum; ultimate segments often articulated; venation free (in sterile fronds) or forming a network, without included veinlets, ending in or near the margin, often in hydathodes. Indumentum composed of unicellular glands on the abaxial surface of the lamina, or needle-like hairs occuring on the axes and lamina and/or scales on the rhizome and stipe. Sori variously arranged, exindusiate or covered by a strongly modified marginal indusium. Sporangia often mixed with paraphyses (sterile hairs).

Note that the term “pteroid” is colloquial shorthand to refer to members of the Pteridaceae, whereas “pteridoid” refers to members of a specific Pteridaceae subclade.

View Pteridaceae Tree

Plastid DNA sequence data suggest that the Pteridaceae comprise five (mostly) well-supported clades (Schuettpelz et al., 2007). The cheilanthoids are sister to the adiantoids (which include both Adiantum and the group formerly referred to as the Vittariaceae); these two clades are together sister to the pteridoids plus the ceratopteroids; and the cryptogrammoids are, in turn, sister to this large clade. Of these five clades, only the cheilanthoids lack strong support, due to some uncertainty about the phylogenetic position of their earliest-diverging branch (the Doryopteris ludens clade—see the cheilanthoid page). These five clades, none of which correspond perfectly with previously recognized families or subfamilies, do show some ecological differentiation. The ceratopteroids contain the aquatic taxa; the pteridoids contain most of the generalist forest understory species; and the cheilanthoids contain most of the xeric habitat specialists.

This phylogenetic structure differs from the most recent formal taxonomic treatments of the family (Kramer, 1990; Tryon et al., 1990), which recognized two families (Pteridaceae and Vittariaceae), and divided the Pteridaceae into six subfamilies: Adiantoideae, Ceratopteridoideae, Cheilanthoideae, Platyzomatoideae, Pteridoideae, and Taenitidoideae. Molecular data demonstrate that the Vittariaceae are nested within Pteridaceae (specifically within the adiantoid clade), and, while the circumscriptions may be close in some cases, none of the formally described subfamilies of Tryon and Tryon (1990; Adiantoideae, Cheilanthoideae, etc.) corresponds perfectly to the informal clades recognized here (adiantoids, cheilanthoids, etc.). A formal revision of Pteridaceae awaits further data.