Serpocaulon A.R.Sm.

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

Serpocaulon A.R.Sm. , Taxon 55(4): 924. 2006.

Serpocaulon comprises about 50 species, all in the Neotropics and subtropics, with Bolivia, the Andes, and southern Brazil, all major centers of diversity. Twenty-one species are known from Bolivia, three recently described ( Kessler & Smith 2005). Characters of the genus include peltately attached, clathrate or subclathrate rhizome scales; adaxially grooved, often stramineous petioles; simple, pinnatifid, pectinate, or fully pinnate blades lacking scales (except sometimes a few along the costae and rachises abaxially); areoles each with a single included veinlet, and sori located on the ends of these free included veins ( Hensen 1990, Smith et al. 2006); and variously tuberculate spores ( Ramírez-Valencia & Sanín 2016). Some species of Campyloneurum have somewhat similar venation, but primary areoles are either completely divided into two areoles by the excurrent veinlet or each areole has two or more included free veinlets. Pecluma , Phlebodium , Microgramma , and Pleopeltis all have different venation, in addition to other distinguishing characteristics. Serpocaulon and most other neotropical genera of Polypodiaceae have been until recently included in Polypodium (e.g., by Hensen 1990), but that genus is now considered to include only a few species of temperate regions and tropical mountains. Species limits within Serpocaulon are problematic, especially the groups around S. richardii / S. fraxinifolium and S. lasiopus / S. loriceum , which are badly in need of detailed study. Characters that can be used to distinguish the Bolivian species of Serpocaulon include: rhizome thickness; rhizome scale density (sparse or completely covering rhizomes); rhizome scale shape (round, oblong, ovate, lanceolate, or long-attenuate); blade dissection (simple, pinnatisect, or 1-pinnate); proximal pinnae (fully adnate, partially adnate, or free); blade apex (pinnatifid vs. conform); number of rows of sori between costae and pinna margins (1, 2, or up to ca. 8) ( Smith et al. 2006). Affinities of Serpocaulon , based on morphology, appear to be with Adetogramma and Microgramma , and probably other neotropical polypod genera, with more distant relationships to Polypodium s.s. and Pleopeltis ( Smith et al. 2006, Almeida et al. 2017). Surprisingly, Serpocaulon (or the clade Serpocaulon + Adetogramma ; Almeida et al. 2017) appears to be sister to the entire grammitid clade based on chloroplast DNA data ( Schneider et al. 2004, Schuettpelz & Pryer 2007); however, nuclear markers are needed to confirm this. Kreier et al. (2008), using AFLP data, explored intergeneric relationships within Serpocaulon and found that a small number of species more distantly related to the rest of the genus were concentrated in southeastern Brazil; species occurring at higher elevations in the Andes were found to be members of more species-rich subclades. Labiak & Prado (2008) provided a treatment and key to the species of Serpocaulon in the coastal Atlantic Rain Forest of Brazil, and Schwartsburd & Smith (2013) described a new species and hybrid from southeastern Brazil, and provided a conspectus of the genus in Brazil.