Polypodiaceae

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

Polypodiaceae subfam. Polypodioideae (historically, “Polypod” ferns)

This subfamily is generally considered non-monophyletic, as circumscribed in PPG I (2016), since the grammitids, treated herein as subfam Grammitidoideae , may be nested in this clade (e.g., Schneider et al. 2004, Schuettpelz & Pryer 2007, Almeida et al. 2017). However, Sundue et al. (2015b) found the genera of this subfamily formed a monophyletic clade when several Asian ( Aglaomorpha Schott , Arthromeris (T.Moore) J.Sm. , Drynaria (Bory) J.Sm. , Selliguea Bory ) genera were included in phylogenetic analysis. Clearly, more data, ideally including nuclear data, are needed to clarify these relationships. As defined by PPG I (2016), Polypodioideae is almost entirely neotropical, with all of the known genera except Pleurosoriopsis Fomin (monotypic, eastern Asia) occurring in the New World. Two largely New World genera— Microgramma and Pleopeltis —do have a few representatives in Africa and nearby islands in the Indian Ocean, and two other genera, Polypodium L. and Synammia C.Presl in Chile and Argentina, do not occur in Bolivia. Polypodium is largely north-temperate and Mexican in distribution, with a few species filtering down into Central America, the Antilles, and northern South America.

Subfam. Polypodioideae , historically called polypods (see Sundue et al. 2014), is characterized by whitish to yellowish (rarely green) bilateral, reniform spores each with a monolete scar positioned proximally (at the confluence of the four daughter spores in the tetrads), sporangial stalks consisting only of two or three rows of cells, and leaf petiolar traces of often three vascular strands. The blades and/or blade axes often (exceptions in Pecluma and Serpocaulon ) bear scales (sometimes sparse) of some kind, contrasting with the condition in subfam. Grammitidoideae . Circumscription of the genera is generally settled and non-controversial except for the limits of Pecluma and Polypodium , and nine genera are recognized in the subfamily (PPG I 2016). One of these, Pleurosoriopsis , is restricted to eastern Asia, Polypodium s.s. is unknown from Bolivia, and Adetogramma is more recently described ( Almeida 2017). Thus, for Bolivia, we recognize eight genera, containing 113 species.

Characters delimiting the genera in subfamily Polypodioideae relate to blade dissection, various types of rhizome and blade scales, venation, and soral patterns. However, simple blades have arisen independently in all of the genera except Pecluma and Phlebodium , perhaps as adaptations to epiphytic, seasonally dry habitats.

Phylogenetic relationships within Polypodiaceae and subfam. Polypodioideae have been explored extensively, with an early overview by Schneider et al. (2004). Smith et al. (2006), Kreier et al. (2008), Salino et al. (2008), Otto et al. (2009), Sprunt et al. (2011), Sigel et al. (2014), and Assis et al. (2016) further examined relationships among individual genera.

Despite both being primarily epiphytic, Polypodioideae has a completely different adaptive strategy than the Grammitidoideae ( Sundue et al. 2015b) . Whereas the latter are specialized to cool and humid habitats, Polypodioideae are most abundant in lowland and often in seasonally dry habitats. Morphological adaptations for these conditions include, among others, thick rhizomes, coriaceous blades, deciduousness, CAM photosynthesis, and water-absorbing blade scales ( Kluge & Kessler 2007). Many species of Polypodioideae , especially in the genus Pleopeltis , are poikilohydric and survive the loss of over 95% of their leaf water content ( Stuart 1968, Helseth & Fischer 2005, Kessler & Siorak 2007). These adaptations have not only allowed polypodioid ferns to become the most species-rich and abundant epiphytic tropical lowland fern group, but also the epiphytic ferns that reach furthest north and into arid tropical habitats ( Zotz 2005, Kessler et al. 2007).