Amauropelta, Kunze, Farrnkr., Kunze, Farrnkr.

Fawcett, Susan & Smith, Alan R., 2021, A Generic Classification of the Thelypteridaceae, Fort Worth, Texas, USA: BRIT Press : 23-24

AMAUROPELTA

Amauropelta Kunze, Farrnkr. 1:86, 109, t. 51. 1843.— Thelypteris subg. Amauropelta A.R. Sm., Amer. Fern J. 63(3):121. 1973.

— TYPE: Amauropelta breutelii Kunze = A.limbata (Sw.) Pic.Serm. [= Thelypteris limbata (Sw.) Proctor ] Oochlamys Fée

Etymology. —Gr. amauros, dark + pelte, shield. Referring to the darkened indusia of the type species; most species in Amauropelta , if indusiate, have tan or stramineous indusia at maturity.

Plants mostly terrestrial, or occasionally cremnophilous or rheophytic, mostly from (10–)30–100(–200) cm tall; rhizomes long-creeping, short-creeping, suberect, or erect, rarely scandent; fronds once-pinnate to usually pinnate-pinnatifid, rarely 2-pinnate or slightly more divided, monomorphic, usually arching; stipes stramineous, brownish, or occasionally atropurpureous, dull to lustrous, stipe bases and rhizome scales dull brown to tan, ovate to lanceolate, rarely glabrous, usually with acicular, hyaline hairs 0.1–0.2 mm on margins and surfaces; blades chartaceous to subcoriaceous, usually drying green, lanceolate, ovate to broadly deltate, proximal pinnae usually greatly to sometimes subabruptly or abruptly reduced, often> 6 pairs, basal pair(s) sometimes auriculiform or glanduliform and <5 mm long, blade apex gradually reduced, with distal pinnae not or only slightly decurrent, proliferous buds absent or infrequently present in axils of distal pinnae in a few spp. (e.g., A. linkiana and related spp. treated in sect. Uncinella by Smith 1974); pinnae shallowly lobed, usually pinnatifid or pinnatisect, rarely 1-pinnate or subentire, rarely entire ( A. reducta ), typically straight, less commonly falcate, sometimes with small acroscopic auricles; veins usually prominent abaxially and adaxially, lowermost pair from adjacent segments running to margin just above sinus between adjacent lobes, rarely running to sinus ( A. linkiana ), never united to form excurrent veins that run to sinuses, veins ending at pinna margins; aerophores absent or, if present, tuberculate or elongate, or with only or a small patch of darkened aerating tissue at pinna bases; indument abaxially usually of hyaline acicular hairs on rachises, costae, veins, and sometimes between veins, indument adaxially of hyaline acicular hairs on rachises and costae, sometimes also on veins and between veins, hairs sometimes appressed, hairs on stipes and rachises short 0.1–1(–2) mm, sparse to dense, plants rarely glabrous or glabrescent, hairs usually single-celled, rarely septate; glands, if present, resinous or hemispherical and translucent, orangish to reddish, sometimes capitate (short-stipitate), light yellowish, borne on laminae and veins; pustules absent on laminar tissue; sori inframedial, medial, or infrequently submarginal, usually round, occasionally oblong or elongate along veins, indusiate or exindusiate, indusia if present round-reniform (lunate in A. decurtata ) or reduced to a fragment, usually whitish or tan when young, occasionally greenish ( A. germaniana ) or blackish ( A. melanochlaena ), persistent to evanescent, hairy and or glandular to glabrous; sporangia usually glabrous, rarely setulose; spores pale brown, lacking pronounced winglike ridges or echinae, reticulate and perforate (fenestrate), with secondary sculpturing of gemmulae (Tryon and Lugardon 1991; Alvarez-Fuentes 2010); x = 29, 27, 31. This heterogeneity in chromosome base numbers in a single genus is unusual in ferns, although it is common among genera of the amauropeltoid clade. The biological significance is yet to be determined; the numbers do not appear to be miscounts.

Diagnosis.— The genus Amauropelta is morphologically most similar to the other two genera of the amauropeltoid clade. It is distinguished from Metathelypteris (eastern Asia) by the veins running to the margins, adaxially grooved costae,base chromosome number of x = 27, 29, 31 (vs.usually x = 35in Metathelypteris ). From Coryphopteris , Amauropelta differs by the combination of usually greatly reduced proximal pinnae, lack of sessile, resinous, reddish glands on the lamina between veins (except in the A. resinifera group), usually creeping or suberect rhizomes (vs. upright and trunklike, except in Coryphopteris simulata ), and usual base chromosome number of x = 29, 27, 31 (vs. x = 31, 32, 33). Holttum (1974a) and Patel et al. (2019a) noted that the spores of species of the amauropeltoid clade are frequently perforate (a rare state elsewhere in the family) but those of Amauropelta are reticulate with low ridges, while spores of Coryphopteris often are winged and fimbriate.

By far the greatest species diversity of Amauropelta is in the Neotropics, but the earliest-diverging lineages are from the Old World. The genus is here broadly defined to include Parathelypteris pro parte (with some species transferred to Coryphopteris ), and is subdivided into four subgenera; two are strictly Old World and two predominantly New World.

Most necessary combinations have been made in Amauropelta , by Holttum (1974a, 1977b), Salino et al. (2015), and Kuo et al. (2019), but new combinations in subgenera Parathelypteris and Nibaa are made below.

KEY TO SUBGENERA OF AMAUROPELTA

1. Proximal pinnae abruptly or little reduced; plants of temperate, or subtropical montane East Asia, mostly winter-deciduous with thin,branching long-creeping rhizomes 1–2.5 mm diam.; x = 27,31 ________________________________________ subg. Parathelypteris

1. Proximal pinnae typically gradually reduced;plants widely distributed;rhizomes various; x = 27,29,31.

2. Rhizomes typically erect,> 3 mm diam.;predominantly neotropical; x = 29 ______________________________________subg. Amauropelta

2. Rhizomes long creeping,<3 mm diam.;temperate or paleotropical; x = 27,31.

3. Plants of temperate North America;glands yellowish or colorless; x = 27 ____________________________________________ subg. Nibaa

3. Plants of temperate East Asia to Malesia;glands resinous yellow-orange to red; x = 31 _________________________________ subg. Venus