Mertensia seminuda Klotzsch (1844: 538). Type:— VENEZUELA. Caracas. Moritz 91 pro parte (lectotype designated here, B [B 20 013 9889] photo!).

Mertensia schomburgkiana Sturm (1859: 233). Dicranopteris schomburgkiana (J.W.Sturm) Morton (1951: 16). Type:— GUYANA. Schomburgk 1671 (lectotype designated here, B [B 20 013 9896], photo!, isolectotype B [B 20 013 9897] photo!).

Plants terrestrial. Rhizomes 2.45–3.85 mm thick, with redish-brown rigid simple or branched hairs, glabrescent. Fronds scrambling, 2–4-forked, ultimate branches 14.5–33.5 × 3.8–7.5 cm, lanceolate, occasionally eliptic, apex pinnatifid, base asymmetric, inner side with reduced segments, external side with conform segments, ultimate segments linear 2.7–4 × 0.23–0.4 cm, margins slightly to strongly revolute, abaxial surface green or pruinose, lanose, with multicellular reddish hairs on midrib and secondary veins, without glandular hairs. Buds covered by multicellular reddish hairs, pseudoestipule present, accessory branches pinnatisect. Veins 3–4-forked. Sori medial, with hyaline paraphyses.

Distribution and habitat: — Brazil (Amazonas), Colombia, and Venezuela. In Brazil it occurs only in the high areas (1150–1250 m) of the Serra do Aracá near the border with Venezuela.

Notes:— Dicranopteris seminuda is morphologically related to Dicranopteris rufinervis but differs form it by the absence of bacilliform glandular hairs on segments secondary veins, slightly patent to retroflex segments, and multicellular hairs on segment midribs, secondary veins, and laminar tissue and blade chartaceous.

In the original description of Mertensia schomburgkiana, Sturm cited Schomburgk 1671 as type material in B, but there are two exsiccatae of this collection. On them, there are recent labels indicating “A” and “B”. However, although both seems to be part of a single specimen, the original labels are not clear about this and thus must be considered as duplicates. For that reason, we chose the most complete specimen as lectotype.

Selected specimens examined: — BRAZIL. Amazonas: Barcelos, Parque Estadual da Serra do Aracá, contrafortes do Pico da Aparecida, 00º56’20”N 63º20’53”W, 30 October 2011, Martinelli et al. 17233 (RB); Platô da Serra do Aracá, parte SE da Serra Norte, 1150–1250 m, 00º51’N 63º22’W, 15 February 1984, Tavares & Silva 52 (K).— COLOMBIA. Antioquia: Belmiria, Vereda Montanita, 6º37’18.7”N 75º40’00.3”W, 2885 m, 17 June 2002, Rodriguez 3406 (COL); Medellin, córrego, Santa Helena, Vda Mazo, caminho que conduce a la estacion biodiversidade, 06º15’45.5”N 75º30’49.5”W, 2450 m, 19 January 2001, Rodriguez 3245 (COL).