Adiantum (PPG I, 2016)

Kessler, Michael, Smith, Alan R. & Prado, Jefferson, 2017, Prodromus of a fern flora for Bolivia. XXVII. Pteridaceae, Phytotaxa 332 (3), pp. 201-250 : 230

Adiantum L., Sp. Pl. 2: 1094. 1753.

Adiantum is subcosmopolitan genus with about 225 species, ca. 110 of them occurring in tropical America. Most of the species are tropical and subtropical, but a few occur in temperate regions. Bolivia hosts 48 species, two of them endemic; 29 of these species are rare or uncommon, with five or fewer known collections in the country. Labiak & Prado (2007) documented the occurrence of a number of new species records for the genus in Bolivia: Adiantum anceps , A. diogoanum , A. dolosum , A. incertum , A. ornithopodum , A. poeppigianum , A. scalare , A. senae , A. sinuosum . Other recently described species from Bolivia are A. solomonii and A. tuomistoanum ( Prado & Smith 2006) and A. camptorachis ( Sundue et al. 2010) .

The genus is characterized by having rhizomes short-to long-creeping, or these sometimes compact and suberect; scales borne at rhizome apices and stipe bases; usually castaneous or atropurpureous stipes and rachises; blades medium-sized to large, monomorphic, pinnate (rarely undivided in a few extraterritorial species) to 3+ times pinnate, sometimes pedate; veins free or infrequently anastomosing without included free veinlets; linear epidermal idioblasts (false veins) present or not between the true veins (see Sundue 2009); sori formed on the recurved blade margins (false indusia), on the veins, without paraphyses; globose to tetrahedral, trilete-scarred spores; and x = 29 or (usually) 30.

Adiantum senae Baker has recently been placed in Adiantopsis ( Schuettpelz et al. 2014) . Species in the A. raddianum group (comprising also A. lorentzii , A. moorei , A. orbignyanum , A. patens , A. raddianum , A. ruizianum , and A. tinctum in Bolivia) were recently studied by Hirai et al. (2016).

Notes on relationships included with individual species below are generally reflective of morphological similarities and also take into account unpublished molecular studies by Huiet et al. (in prep.)—a global study of Adiantum that includes nearly 150 species. By far the most diverse subgroup of species in the Neotropics, and in Bolivia, is the Adiantum tetraphyllum clade, comprising over 50 species total and ca. 24 species in Bolivia. These have dimidiate segments, conspicuous idioblasts in laminar tissue, scales and/or hairs on the axes and sometimes on the blades, and mostly 2-pinnate blades with a conform apical pinna; there are also a few species in this clade that are 1-pinnate, e.g., A. dolosum , A. lucidum , A. petiolatum ). Other recognizable clades in Bolivia include more dissected, large species related to A. pectinatum (also A. trapeziforme , A. mathewsianum ); the A. raddianum / poiretii clade (including also A. moorei and A. orbignyanum ), with fan-shaped, smaller, usually glabrous segments and axes, and distal sori; and the A. anceps / peruvianum clade, with large, ovate segments.