Dicksonia stuebelii, Hieron., Hedwigia

5. DICKSONIA STUEBELII Hieron. View in CoL ,

Hedwigia 45: 228, t. 12, f. 1. 1906.

TYPE: PERU. Amazonas: Tambo Ventilla, Pascomayo to Moyobamba, A. Stübel 1076 (lectotype B-20_0138741 , inadvertently designated by Tryon 1989: 105; isolectotype [original drawing] B-20_0138743 ).

Trunks to 4 m, but fertile plants can also be trunkless, 10–15 cm in diam, with additional cover of adventitious roots of varying extent, dead fronds persisting for some time, but not forming skirt below crown; adventitious buds lacking. Fronds to 150 cm long, monomorphic, erect, larger ones slightly arching distally. Petioles short, not longer than 21 cm and then appressed to the trunk for most of their length, at base covered with soft, catenate hairs to 3.5 cm long, yellowish to orange at the very base, changing to stronger, more ciliform hairs to 4.5 cm, reddish, in upper parts, additionally covered with a whitish, woolly undercoat extending onto the rachis. Laminae to 150 X 40 cm, bipinnate-pinnatifid, oblanceolate, firmly coriaceous. Frond axes (rachises, costae, and costules) smooth to slightly rough, densely covered with whitish, woolly hairs, matted, persistent. Pinnae to 20 X 3.8 cm, sessile, triangularlanceate with attenuate tips, ca. 22–28 pairs per frond. Pinnules to 2.1 X 0.5 cm, sessile, basally slightly auriculate, linear-oblong, with obtuse to short acute tips. Segments to 2 X 2 mm, sessile, isodiametric, round, margins revolute. Veins abaxially covered with whitish hairs, adaxially glabrous. Sori 1.2–1.5 mm in diam, round to weakly kidney-shaped when closed, circular when open, one sorus per segment on the acroscopic side of the segment; indusia bivalved, outer one green to grayish brown with pale cartilaginous margin, inner one pale brown to grayish brown with undulate margin; paraphyses of the same length as sporangia, catenate, tortuous, forming a conglomerated mass. Spores tetrahedral-globose with prolonged, depressed lobes, spores not measured, exospore smooth, perispore bacillar-granular. Figures 1C, G View FIG , 7B View FIG .

Etymology —The name commemorates M. Alphons Stübel (1835–1904), German geologist who explored South America in 1868–1877, gathering a broad spectrum of data and material, including the type of the species.

Distribution and Habitat —Presumably endemic to the Huancabamba region of northern Peru, in stunted, high montane forests scrub and páramos at 2410–3450 m; one record from northern Colombia may represent this species ( Fig. 6 View FIG ).

Additional Specimens Examined — Colombia. — CESÁR: Sierra de Perijá, 25 km E of Codazzi , on the Venezuelan border, [ca. 10°00 ' 50"N, 72°57 ' 28"W,] 3200 m, 16 Feb 1945, M.L. Grant 10975 ( COL) GoogleMaps . Peru. — AMAZONAS: Mendoza, 06°14.083’S, 77°36.035’W, 2487 m, 11 Aug 2010, M. Lehnert 2016 ( BONN, USM), M. Lehnert 2019 ( BONN, USM) GoogleMaps ; 06°12.845’S, 77°40.656’W, 2413 m, 11 Aug 2010, M. Lehnert 2021 ( BONN, USM) GoogleMaps ; Chachapoyas, upper slopes and summit of Cerrro Yama-Uma above Taulia , 12–15 km SE of Molinopampa, [06°12 ' 27"S, 77°40 ' 07"W,] 3200–3450 m, 11 Aug 1962, J.J. Wurdack 1679 ( K, UC) GoogleMaps .— CAJAMARCA: Santa Cruz , 06°39 ' 26"S, 79°01 ' 31"W, 3280 m, 02 Nov 2001, V.I. Sanchez and M. Sanchez 1111 ( UC) GoogleMaps .

Notes — Dicksonia stuebelii is easily separated from D. navarrensis , D. karsteniana , and D. sellowiana by the shape of the pinnules (linear-oblong in D. stuebelii vs. oblong-lanceolate in D. navarrensis , D. karsteniana , and D. sellowiana ) and segments (isodiametric, rounded vs. oblong, often falcate) as well as the position of sori (restricted to the acroscopic side vs. on both sides). Dicksonia stuebelii is the only species of the genus in South America that is regularly fertile when being trunkless (but see discussion of D. karsteniana var. karsteniana ). Dicksonia stuebelii and D. lehnertiana both have relatively narrow fronds and dense laminar pubescence abaxially, including at least some hairs present between the veins, but each species has completely different hairs on petioles and frond axes (soft woolly appressed in D. stuebelii vs. spreading, stiff bristles in D. lehnertiana ).

In the Cordillera Colán, Dicksonia stuebelii occurs practically side by side with D. karsteniana , which here grows in small forest patches within the open páramo (AT pers. obs.). A similar setting is found between Molinopampa and Mendoza, where white sandstone outcrops alternate with swampy areas, and a notable increase of humidity from west to east. This region has experienced severe deforestation during the last two decades (ML pers. obs.), which apparently fostered the contact between the two species: Dicksonia karsteniana survives the clearing of the forest as stunted plants whereas D. stuebelii expands into the secondary scrub from the natural karst areas. Under these conditions, D. karsteniana (i.e. var. archneosa ) approaches the phenotype of D. stuebelii in having small pinnules with revolute margins and dense persistent hairy indument on the frond axes. Nevertheless, the diagnostic features as given in the key remain valid, although the possibility of natural hybrids between the two species (putative hybrid Lehnert 226) cannot be discarded.

Specimens of Uncertain Identity —E.L. Little, Jr. 9015.— Colombia.— HUILA: Camp on W side of R´ıo Venadito, 25 km SE of La Bodega, [ca. 03°09 ' 15.3"N, 74°45 ' 57.4"W] 2390 m, 01 Dec 1944 (COL-000279175). This specimen has large pinnules (to 11 X 3 cm) with erect, red to bicolorous hairs abaxially on costae, costules, and veins. With its large sori (1.6–2.0 mm diam.) and its adaxially dark lamina, it most resembles Dicksonia lehnertiana and may represent a hitherto unknown extreme in size. However, without the petioles, which should bear bristly hairs, its identification remains uncertain. The frond axes bear remnants of short erect red hairs but the abraded areas are smooth, not scabrous as would be expected from D. lehnertiana . Adding the distance between the localities, we find it advisable to first try to gather more material of this phenotype before making a decision whether to treat it as a separate species or to accommodate it within the description of D. lehnertiana .