(3006) Proposal to conserve the name Sticherus (Gleicheniaceae) with a conserved type

Abstract

(3006) Sticherus C. Presl [Tent. Pterid.] in Abh. Königl. Böhm. Ges. Wiss., ser. 4, 5: 51. 1836 (ante 2 Dec), nom. cons. prop.

Typus: S. gracilis (Mart.) Copel. (Gen. Fil.: 27. 1947) (Mertensia gracilis Mart.), typ. cons. prop.

Sticherus is the largest genus in Gleicheniaceae, comprising about 95 recognized species (Gonzales & Kessler in Phytotaxa 31: 1–54. 2011; PPG I in J. Syst. Evol. 54: 563–603. 2016; Lima & Salino in Phytotaxa 358: 199–234. 2018). It is found in the tropics of Africa, Asia, Oceania, and the Americas, with the latter area harboring the majority of the species (Holttum in Fl. Males., Ser. 2, Pterid. 1: 1–36. 1959; Gonzales & Kessler, l.c.; PPG I, l.c.). The genus was established by Presl (Tent. Pterid.: 51–52. 1836) and initially included two species: Sticherus laevigatus (Willd.) C. Presl and S. laniger (D. Don) C. Presl. However, the latter species is now widely recognized not to belong to Sticherus (Pichi-Sermolli in Webbia 26: 491–536. 1973) and is currently included in Dicranopteris (Fraser-Jenkins, Taxon. Revis. Indian Subcont. Pterid.: 35. 2008). Sticherus was first typified by Pfeiffer (Nomencl. Bot. 2: 1285. 1874), who designated S. laevigatus (Mertensia laevigata Willd., Sp. Pl. 5: 75. 1810) as type. Christensen (Index Filic.: LIV, 627. 1906) originally included Sticherus within Gleichenia sect. Holopterygium Diels, when adopting a monogeneric classification for Gleicheniaceae, but, subsequently (in Verdoorn, Man. Pterid.: 530. 1938) he recognized Sticherus in his classification system, now with five genera for Gleicheniaceae, and also adopted S. laevigatus as the type of the generic name.

Sticherus laevigatus has been widely treated as a synonym of S. truncatus (Willd.) Nakai (e.g., Holttum, l.c.; Pichi-Sermolli, l.c.: 524; Gonzales & Kessler, l.c.), based on Mertensia truncata Willd. (in Kongl. Vetensk. Acad. Nya Handl. 25: 169. 1804) an earlier name than M. laevigata Willd. The first author carefully reviewed the original elements of these two species in Willdenow's collection housed at B (B -W 19470 -01 0 and B -W 19471 -01 0), also confirming without any doubt the synonymy.

Species delimitation within Sticherus is complex, primarily based on the indumentum and secondarily on blade architecture and rhizome features. The genus underwent revision by Gonzales & Kessler (l.c.) and was later revisited by Lima & Salino (l.c.) and Lima & al. (in review). The same authors (Lima & al. in Molec. Phylogen. Evol. 184: 107782. 2023), in a phylogenomic study with an extensive geographic sampling of the genus, found Sticherus to be paraphyletic. In that study, the genus forms two clades, Sticherus s.str., including S. laevigatus, the type of the generic name, and S. milnei (Baker) Ching, as sister to a larger clade comprising Stromatopteris and Gleichenia, which in turn is sister to the remaining species of Sticherus (referred to here as the aff. Sticherus clade; Lima & al., l.c. 2023). Divergence time estimates suggest that the split between Sticherus s.str. from the Gleichenia + Stromatopteris + aff. Sticherus clade occurred around 114–117 million years ago, with the latter diverging from Stromatopteris and Gleichenia at approximately 111–113 million years ago (Lima & al., l.c. 2023). Sticherus s.str. is characterized by having an anisotomic branching pattern, whereas the species in the aff. Sticherus clade are characterized by having an isotomic branching pattern. The aff. Sticherus clade has a pantropical distribution with most of its species occurring in the Neotropics (about 54 species), whereas the Sticherus s.str. clade (S. laevigatus, S. milnei) occurs only in Australasia (Holttum, l.c.; Chinnock & Bell in Fl. Australia 48: 148–162. 1998; Gonzales & Kessler, l.c.; PPG I, l.c.).

To achieve monophyletic genera, both clades must be recognized as distinct genera. Following the principles of the ICN, the name Sticherus would be applied to the Sticherus s.str. clade, encompassing two species (S. laevigatus, S. milnei). Since there is no other available generic name to accommodate the remaining species of Sticherus, a new generic name would be necessary, along with the combination of 95 species names into this new genus. Alternatively, an option is to conserve the name Sticherus with a species from the aff. Sticherus clade and describe a new genus to include the two species from the Sticherus s.str. clade, S. laevigatus, and S. milnei.

The usage of Sticherus is well-accepted in various floras, including those of Bolivia (Kessler & Smith in Phytotaxa 344: 053–063. 2018), Brazil (Lima & Salino, l.c.), Colombia (Murillo-P. & al. in Bernal & al., Cat. Pl. Liquenes Colombia: 158–166. 2016), Mexico (Mickel & Smith, Pterid. Mexico: 604–607. 2004), Africa (Roux in Strelitzia 23: 50. 2009), and Australia (Chinnock & Bell, l.c.). Furthermore, many of these “aff. Sticherus” species are both common and abundant, showing a preference for colonizing open and disturbed habitats (Holttum, l.c.; Gonzales & Kessler, l.c.; Lima & Salino, l.c.). As a consequence, these species names are widely used by botanists and conservationists, and the genus is frequently well represented in herbaria worldwide so that, e.g., there are 34,295 records of Sticherus on GBIF (https://doi.org/10.15468/dl.gs427j) and 11,431 records on Pteridoportal (https://www.pteridoportal.org/portal/index.php, accessed 6 Sep 2023). Changing the names of 95 species across the globe's specimens would be highly time-consuming and could take decades. Also, the name Sticherus has been used in many publications (e.g., a search for Sticherus on Google Scholar retrieved 2150 entries). In this context and to maintain nomenclatural stability, we propose to conserve the name Sticherus with a new type, S. gracilis (Mart.) Copel. This species is well resolved in the aff. Sticherus clade (Lima & al., l.c. 2023), is from the Neotropics (the diversity center of the genus), has an isotomic branching pattern, and is a properly typified name with a well-preserved and complete type specimen (Lima & Salino, l.c.). The morphology of this species aligns with the typical description of Sticherus adopted in worldwide floras and revisions.

Under this proposal, the names of all Sticherus species would be preserved, except for the two species of the Sticherus s.str. clade. By doing so, nomenclatural stability would be prioritized, preventing the need for 95 new combinations. Therefore, we propose to conserve the name Sticherus. The only argument against the conservation of Sticherus with the conservation of its current type lies in the inobservance of the priority principle of the ICN.