Novelties in Adiantum (Pteridaceae) from South America

Abstract: We describe two new species of Adiantum (Pteridaceae): A. nodosum and A. pseudocajennense. These species occur in the lowland rainforests of the Amazon Basin at 100–350 m in elevation. Both species have laminae 2-pinnate and grow on waterlogged soil in tall swamp forests, but they differ in the rhizome diameter and degree of incision of the pinnule margins. Currently available information suggests that A. pseudocajennense may be endemic to Ecuador, whereas A. nodosum has a wider distribution and is known from Brazil, Colombia and Peru. For both species we present descriptions, distribution statements, comments and illustrations. Citation: Prado J., Hirai R. Y., Smith A. R. & Tuomisto H. 2017: Novelties in Adiantum (Pteridaceae) from South America. — Willdenowia 47: 237–242. doi: https://doi.org/10.3372/wi.47.47307 Version of record first published online on 13 November 2017 ahead of inclusion in December 2017 issue.


Introduction
Adiantum l. is a large genus described by linnaeus (1753) with a worldwide distribution (mickel & smith 2004). the genus is monophyletic (rothfels & schuettpelz 2014;Pryer & al. 2016;PPg i 2016) and has about 225 species. it is characterized by terete, blackish to castaneous petioles, rachises and costae, and sporangia borne on the false indusium (i.e. not on the abaxial laminar surface below it). the rhizomes are short-to longcreeping, usually horizontal, but sometimes compact and suberect, with scales. laminae are monomorphic or nearly so, pinnate (rarely undivided) to 5-pinnate, sometimes pedate with free or rarely anastomosing veins without included free veinlets and with or without linear epidermal idioblasts (false veins) between the true veins. sori are formed on the veins of the recurved laminar margins (false indusia), and paraphyses are absent.
our recent studies and those of others have revealed several new Adiantum species for south america in the last 11 years, e.g.: Peru, one species (Prado 2006); Bolivia, one species (Prado 2006); argentina, one species (sundue & al. 2010); ecuador, one species (mcCarthy & Hickey 2011); Brazil, one species (Prado & Hirai 2013); french guiana, one species (Zimmer 2007); guyana, one species; and french guiana, three species (Boudrie & al. 2017). the two new species described here represent one more step in the process to understand the diversity of Adiantum in the amazon region.

Material and methods
this study is based on specimens from the following herbaria: amaZ, CoaH, CuZ, inPa, nY, QCa, QCne, sP, tur, uC, us and usm. species recognition was based on morphological characters such as rhizomes, scales, laminar dissection, indumentum and pseudoindusia. We have illustrated the most distinctive characters for each species.
Bracketed geographic coordinates were estimated based on the closest localities, when that information was not given on the specimen label.

Results and Disussion
Etymology -the specific epithet is based on the morphology of the rhizome, with approximate stipes, leading to a nodose appearance of the rhizomes. this feature is more evident on small specimens where the stipes are 1 -1.5 mm apart.
Adiantum nodosum resembles Adiantum tetraphyl lum, but the latter differs in having thicker rhizomes (> 5 mm in diam.), sterile pinnules with acute apices that are curved toward the pinna apices, and rachises with filiform scales adaxially and lanceolate scales abaxially. additionally, in A. tetraphyllum the terminal pinnule of each pinna is long-linear (vs. broadly rhombic), and the indusia are shortly oblong and pubescent (vs. lunate and glabrous).
Distribution and ecology -endemic to amazonian ecuador ( fig. 1). occurring in swamp forests dominated by Mauritia l. f. palms and in floodplain forests, usually on muddy sites, at 200 -300 m.
Etymology -the specific epithet is based on the morphological similarity between the pinnules of this new species and those of Adiantum cajennense Willd. ex Klotzsch.