Grammitidoideae

Smith, Alan R., Kessler, Michael, León, Blanca, Almeida, Thaís Elias, Jiménez-Pérez, Iván & Lehnert, Marcus, 2018, Prodromus of a fern flora for Bolivia. XL. Polypodiaceae, Phytotaxa 354 (1), pp. 448-450 : 448-450

Subfamily Grammitidoideae : Grammitid ferns

Grammitid ferns form a monophyletic clade in phylogenetic analyses, but this clade is nested within Polypodiaceae . Chloroplast data show grammitids to be sister to species now placed in Serpocaulon ( Schneider et al. 2004, Schuettpelz & Pryer 2007), Serpocaulon + Adetogramma ( Almeida et al. 2017) , or to a large clade including 12 genera of subfam. Polypodioideae and some Old World genera of subfam. Drynarioideae ( Sundue et al. 2015b) . However, no nuclear markers have been used in assessing these relationships. The sister-group relationship of the grammitid clade to Serpocaulon is not supported by any known morphological similarities and seems very puzzling; a sister-group relationship to a larger Polypodioideae clade seems more likely.

Nearly all grammitids have green tetrahedral spores (exceptionally monolete in some species of Alansmia ), sporangial stalks consisting only of one row of cells, and leaf traces usually of a single vascular strand. Circumscription of the genera has been heavily revised in recent years, and in Bolivia there are 14 genera and 94 species. Before a flurry of taxonomic activity beginning in the 1970s and 1980s by Earl Bishop, genera of grammitids were mostly based on blade division: simple-bladed species were often placed in Grammitis (e.g., by Copeland 1952a); narrow-bladed species with serrulate, pinnatifid, or pinnatisect species were placed in Xiphopteris (e.g., by Copeland 1952b); and broad-bladed, pinnatifid, pinnatisect, or more divided species were placed in Ctenopteris (e.g., by Copeland 1956). Somewhat later, some pteridologists subsumed nearly all members of subfamily Grammitidoideae (often treated as a family, Grammitidaceae ) in a single, very broadly defined genus, Grammitis (e.g., Morton 1967, in his treatment for Ecuador). Nowadays, these generic concepts are considered artificial and inconvenient, and do not reflect intricate and fascinating inter-relationships. In this work, we mostly follow the classification for neotropical genera proposed by Smith (1993), which has been corroborated, in part, by molecular data (see, especially, Ranker et al. 2004, Labiak et al. 2010 a, Sundue et al. 2010, 2014), although Terpsichore as delimited by Smith (1993) is now thought to be polyphyletic and circumscription of other genera has been revised in small or sometimes more significant (and nontrivial) ways ( Sundue et al. 2010, 2014). In this work, we here also recognize five recently segregated genera, namely Alansmia , Ascogrammitis , Galactodenia , Mycopteris , and Stenogrammitis occurring in Bolivia. The delimitation of the grammitid genera as treated here is based on sometimes cryptic characters such as soral paraphyses, hydathodes, rhizome scales, and hair types. Blade dissection is highly variable within many genera and distantly related species can look alike, superficially.

Grammitidoideae is a pantropical subfamily of over 750 species, with only a few species in temperate or even subtropical regions. Sundue et al. (2014) have explored the global phylogeny and biogeography of the grammitid ferns, including 31 of 33 recognized genera in the clade. Their results support several noteworthy phylogenetic and biogeographic patterns: (1) a monophyletic grammitid clade that arose among neotropical polypod ancestors about 31.4 Ma (including Terpsichore s.s., Cochlidium , and Grammitis s.s.); (2) a paraphyletic assemblage of clades distributed in the Neotropics and the Afro-Malagasy region (including most other neotropical genera) ( Bauret et al. 2017); (3) a large clade distributed throughout the Asia– Malesia –Pacific region that originated about 23.4 Ma; and (4) an Australasian clade comprising the circumaustral genus Notogrammitis Parris. Thus , the large grammitid clade appears to have arisen and radiated in the Neotropics, before dispersing more recently to Africa, Asia, Polynesia, and Australasia.

Ecologically, the grammitid ferns (subfam. Grammitidoideae ) are essentially an epiphytic radiation, with a number of species also growing on rocks, and others on the ground mainly in tropical alpine habitats above the upper tree line. Very few species grow on humus-rich forest floor habitats in montane forests. In contrast to the generally very hardy members of most other subfamilies of the Polypodiaceae , from which they originated, they usually have very small rhizomes that are very susceptible to damage. Indeed, despite numerous attempts, we have not been able to transplant species of grammitid ferns even within their natural habitat, with the exception of Cochlidium serrulatum (M. Kessler, M. Lehnert, unpubl. data). This may reflect a close association of these ferns with specialized mycorrhizal fungi ( Lehnert et al. 2016). In montane cloud forests, grammitid ferns are among the most abundant and diverse epiphytic plant groups, with up to 20 species growing together on 400 m 2 ( Kessler et al. 2001, M. Kessler unpubl. data). On the other hand, anecdotal evidence suggests that many species have massively declined in abundance at sites where a few decades ago they were common. This has been observed in Borneo (B.S. Parris pers. comm.), Brazil (J. Prado pers. comm.), and Bolivia (M. Kessler pers. obs.) and may reflect the reduction of mist frequency due to deforestation and climate change. Accordingly, grammitid ferns, many of which are only known from very few collections, may be among the most threatened fern groups.