Amauropelta subg. Amauropelta

Fawcett, Susan & Smith, Alan R., 2021, A Generic Classification of the Thelypteridaceae, Fort Worth, Texas, USA: BRIT Press : 24-25

Amauropelta subg. Amauropelta

Diagnosis.— Amauropelta subg. Amauropelta may be distinguished from other subgenera of Amauropelta by x = 29, and rhizomes typically erect, and> 3 mm diameter.

Biogeography and ecology.— Amauropelta is the largest genus within the family, and subg. Amauropelta is by far its largest subgenus, with 223 of the 233 species recognized here ( Almeida et al. 2016; Salino et al. 2015) ( Fig. 1 ). The greatest center of diversity in the Neotropics is in the South American Andes, but important secondary centers are in the Antilles, Mesoamerica, Venezuela, and southern Brazil. It is likely that there remain dozens of undescribed species, especially in Andean countries— Colombia to Bolivia —and it is evident that much of the speciation has occurred concomitant with the recent uplift of the Andes. Species are found from near sea level to over 4000 m.

Members of this subgenus are globally distributed, representing complex biogeographical patterns (see below). Species of subg. Amauropelta are found generally in primary, undisturbed forests, partially disturbed forests, forest margins, and even sometimes in open areas; occasionally they grow on rocks, and on streamsides, where they tend to have smaller, more streamlined blades and can be considered rheophytes (e.g., A. sancta .) A few species are weedy and found especially along roadsides, trails, and wet ditches (e.g., A. rudis ).

Taxonomic and phylogenetic studies. —The African and Pacific island species of subg. Amauropelta represented by molecular data are nested within the neotropical radiation ( Almeida et al. 2016; Patel et al. 2019a; Fawcett et. al. in press). These include one species in Hawaii ( A. globulifera (Brack.) Holttum ) and two in Polynesia ( A. grantii (Copel.) Holttum , Society Isl.; A. margaretae (E.D. Brown) Holttum , from Rapa) ( Holttum 1977b). There are also nine species in southern and tropical Africa and offshore islands in the Indian Ocean: the six treated by Holttum (1974a) plus A. odontosora (Bonap.) Holttum from the Ivory Coast, A. salazica (Holttum) Holttum , from Réunion and initially placed by Holttum (1974a) in Parathelypteris , and Amauropelta knysnaensis (N.C. Anthony & Schelpe) Parris , from South Africa. A species described from Sri Lanka, A. hakgalensis Holttum , is related to the neotropical species A. oligocarpa (Fawcett et al. in press) and may be an escape from cultivation in the botanical garden nearby.

The neotropical species, treated by Smith (1974, 1982, 1990) as subg. Amauropelta within Thelypteris s.l., have been recognized as a natural group for more than a century ( Christensen 1907, 1913) and treated (usually as Thelypteris ) in floristic accounts for many countries, e.g., Mexico ( Mickel & Smith 2004), Mesoamerica ( Smith 1995a), Jamaica ( Proctor 1985), Puerto Rico ( Proctor 1989), Lesser Antilles ( Proctor 1977), Venezuelan Guayana ( Smith 1995b), Ecuador ( Smith 1983), Peru ( Smith 1992), and Bolivia ( Smith & Kessler 2017). Smith (1974) divided them into nine sections, based on morphological characters of the rhizomes, stipes, aerophores, buds, blade shape, sori, and indusia (or lack thereof). Some of these sections correspond to clades within Amauropelta , e.g., Uncinella, Lepidoneuron, and Amauropelta , but all will need either minor adjustments or major recircumscriptions as a result of recent molecular data ( Almeida et al. 2016, Alvarez-Fuentes 2010, Fawcett et al. in press). Within subg. Amauropelta , molecular sampling is still inadequate to arrive at any meaningful infrageneric boundaries, with 59 of about 233 species sequenced by Fawcett et al. (in press), and an additional 14 species sampled by Almeida et al. (2016).

In broadly based molecular analyses, Amauropelta s.s. is either sister to, or intercalated with, species previously treated as Parathelypteris , from eastern Asia and North America, though with low support. The relationship among the four subgenera is not well resolved (e.g., in the coalescent analysis of Fawcett et al. in press), but each is monophyletic, as is the genus Amauropelta s.l. This combined clade is part of a larger clade that also includes Metathelypteris and Coryphopteris , the ‘ACMP’ clade sensu He & Zhang (2012) or amauropeltoid clade sensu Almeida et al. (2016), Fawcett et al. (in press). Metathelypteris and Coryphopteris are each monophyletic when certain species heretofore treated in Parathelypteris are transferred to Coryphopteris . All members of the amauropeltoid clade have free veins (not anastomosing to forming an excurrent vein to the sinus), usually rather thin-textured blades, sessile or resinous glands on the blades of many spp., and indusiate sori with round-reniform indusia (except many subgroups within Amauropelta , where indusia have been lost, probably along multiple evolutionary lines; see Smith 1990). Although Parathelypteris has long been recognized as a distinct genus, expanding the concept of Amauropelta to include part of Parathelypteris has recently gained favor ( Chang et al. 2019).

Outside of the amauropeltoid clade, Amauropelta spp. are similar to the more distantly related Pseudocyclosorus , which also has free veins, and many pairs of gradually reduced proximal pinnae. Historically, many species of Amauropelta acquired names in Aspidium, Nephrodium, Dryopteris , and Lastrea, the last an illegitimate name now considered to be a synonym of Oreopteris ( Holub 1969) , native to north-temperate areas (which see for discussion). Oreopteris also has reduced proximal pinnae similar to many Amauropelta spp. , but x = 34, different spore ornamentation (echinate or winged vs. reticulate and perforate in Amauropelta ; Wood 1973; Tryon & Lugardon 1991).

Figures

FIG. 1. A synoptical treeillustrating relationships among genera of Thelypteridaceae based on Fawcett et al.(in press).