Rumohra ponceana Arana, Luna & Giudice, 2021

Arana, Marcelo D., Luna, María Luján, Berrueta, Pedro C., Martinenco, María Luz & Giudice, Gabriela E., 2021, Rumohra ponceana (Polypodiales: Dryopteridaceae): a new species from Pampean biogeographic province in Argentina, Phytotaxa 521 (1), pp. 27-38 : 29-35

Rumohra ponceana Arana, Luna & Giudice , sp. nov.

Type: ARGENTINA. Buenos Aires: Partido Tandil , “La Cascada”, November 1967, E. R. de la Sota 5283 (Holotype: LP 082551!) ( Figs. 1–5 ) .

Diagnosis— Rumohra ponceana is distinguished from the Argentinian specimens referred to Rumohra adiantiformis by the presence of conspicuous, capitate glandular hairs with exudate on the margins of rhizome and petiole scales, versus scales with almost entire or slightly dentate margins, without such capitate, glandular hairs. Laminae proximally 2-pinnate-pinnatifid, only in the basal segment, versus laminae proximally 3-pinnate-pinnatifid. The spores brown to dark brown, 40–50 µm in equatorial diameter and 30–35 µm in polar diameter, laesura 20–25 µm long, covered with tubercles, perispore folded, projecting in irregular, large tubercles throughout its surface, versus spores light brown, 25–27 µm in equatorial diameter and 18–20 µm in polar diameter, laesura 10-15 µm long, straight and tenuimarginate, perispore rugulated in polar view and rugulate and folded in distal view, with scattered and irregular, smaller tubercles in Rumohra adiantiformis .

Plants epipetric or growing in rock crevices; roots inserted ventrally; rhizomes creeping, densely scaly, the scales up to 10–13 × 5–6 mm, ovate, basifixed, base slightly cordate, the apex acute, the margins entire to denticulate, with bicellular clavate glandular hairs with exudate, medium brown, sub-clathrate ( Fig. 3 A–E ); leaves dorsal, 25–55 cm long, monomorphic; petioles 10–30 cm × 2.0–5.0 mm, brown, grooved adaxially, moderately to densely scaly throughout, the scales basifixed with large overlapping auricles (pseudopeltate), up to 10–13 × 7–8 mm, mediumbrown, bicoloured with darker centres, sub-clathrate, the apices long-attenuate to filiform, tortuous, the margins entire to denticulate with bicellular clavate glandular hairs with exudate ( Fig. 3 F–K ); laminae 18–36 × 15–23 cm, chartaceous or subcoriaceous, bicoloured, with a lighter abaxial surface, always erect, rhombic, sometimes broadly lanceolate, proximally 2-pinnate-pinnatifid (only the basal segment), becoming gradually less divided toward the pinnatifid apex ( Fig. 2A ); rachises abaxially rounded, adaxially with a central raised ridge flanked on both sides by a groove and lateral ridge, the lateral ridges continuous with the leaf margin; rachis scales like those of the petioles but smaller (up to 2–3 × 0.5–0.7 mm) and bases with ciliate margins ( Fig. 3 L–N ); 5–8 pinnae pairs, lanceolate, with 8–16 segments, the segment margins coarsely serrate, abaxial lamina surface scaly, the scales like those of the rachis but slightly smaller (up to 2 × 3–4 mm) and concolorous ( Fig. 3 O–Q ); sori roundish, medial, indusiate ( Fig. 2 B ), paraphyses absent, receptacle brown to black, indusium peltate, roundish, 1.0– 1.5 mm diam., deciduous, glabrous; spores ellipsoidal, monolete, brown to dark brown, 40-50 µm in equatorial diameter and 30–35 µm in polar diameter, laesura 20–25 µm long covered with tubercles. Perispore folded, projecting in irregular tubercles densely distributed throughout the spore surface. Small, low folds of various shapes occur between the tubercles ( Fig. 4 A–D ).

Distribution and habitat: —This species is known only from Tandilia and Ventania Mountain Systems, in Southern Buenos Aires. Biogeographically, these very ancient Systems are part of the Austral Pampean district, Pampean biogeographic province ( Arana et al. 2021). The orographic systems of Tandilia and Ventania emerge above the Pampas plains where a high biodiversity and ecological heterogeneity occurs. In these orographic systems, the climate is temperate to cold and dry, and snowfalls can occur during winter. The flora that has developed in these environments has different morpho-anatomical adaptive characteristics ( Kristensen& Frangi,2015)and biogeographical relationships with the tropical, subtropical and Subantarctic Andes, Southern Brazil and other mountainous areas in central and North-Western Argentina ( Crisci et al., 2001, Arana et al., 2013). The prevailing vegetation is the grass steppe dominated by many species of genus Nassella ( von Trinius 1830: 73) Desvaux (1854: 263) combined by shrublands ( Arana et al., 2021). The rock outcrops are an exclusive habitat of the mountains where ferns, sub-shrubs, forbs, grasses and graminoids occur ( Fig. 5 A ). Rumohra ponceana grows particularly in sunny rock crevices, with scant soil development and water retention ( Fig. 5 B–C ).

Conservation status:— Tandilia and Ventania Mountain systems together cover an area of 15014 km 2. Rumohra ponceana is found only in six localities, with an area of occurrence considerably smaller than 2000 km 2. Fieldwork suggests that most of its individuals are found in small and relatively isolated subpopulations, occupying very specific habitats, and most populations are under continuing decline owing to removal for commercialization and invasion of the species habitat by alien woody plants. Only few localities are under protection category with protected areas. These data suggest a provisional inclusion of Rumohra ponceana as Vulnerable (VU B1), according to IUCN Red List categories and criteria ( IUCN 2012). Further research on the conservation status of this species is needed, particularly concerning to the degree of reduction in population size owing to removal for commercialization.

Etymology: —The species is named in honor of Dr Mónica Ponce (Instituto de Botánica Darwinion, SI), one of the most relevant fern specialists in Argentina, whose floristic and ecological investigation started with the fern flora from Tandilia and Ventania Systems, in Buenos Aires province. She has made, and still does, very important contributions to Pteridology, especially concerning Argentinian fern flora, biogeography, ecology, systematics and taxonomy.

Additional specimens examined:— ARGENTINA. Prov. Buenos Aires: Azul, sierras de Azul, 20 October 2005, G . Delucchi 2950 ( LP); Balcarce, Sierra Vigilancia, November 1967, E. R . de la Sota 5291 ( LP); 27 November 1985, C . Villamil 3599 ( SI); General Pueyrredón, 2 November 1944, A . Cabrera 9932 ( SI). Sierra de los Padres, 28 December 1986, De Vreese s.n. ( LP); Tandil , 25 November 1937, N . Troncoso s.n. ( SI 1291 ); Tandil, 225 m a.s.l, among rocks, 18 November 2009, F . Zuloaga 11400 ( SI). Tandil , 9 February 1951, D. Abbiatti 4495 ( SI); Tornquist, Sierra de la Ventana, Estancia “Sierras Grandes”, Quebrada del arroyo San Bernardo, 15 March 1980, Proyecto Ventania 1035 ( LP) .

Discussion:—The delimitation of species used here follows the morphological cluster species concept ( Mallet 1995), i.e., “assemblages of individuals with morphological features in common and separated from other such assemblages by correlated morphological discontinuities in a number of features”, in combination with a very distinctive geographical range of distribution. This combination of properties serves as important operational criteria or lines of evidence relevant to assessing the separation and divergence of lineages ( De Queiroz 2007).

Field observations made on living plants, along with observations of herbarium specimens from the whole distribution range in Argentina, led us to find various differences in the laminae architecture as well as the rhizome and petiole scales and the spore morphology that allow distinguishing Rumohra ponceana from the widespread Rumohra adiantiformis . The lamina of Rumohra ponceana is always erect, less divided than the specimens referred to Rumohra adiantiformis (with the lamina often reflexed). The presence of conspicuous, capitate glandular hairs with exudate on the scale margins of rhizome and petiole distinguish R. ponceana from the Argentinian specimens of Rumohra adiantiformis . Also, the spores of Rumohra ponceana are brown to dark brown in colour, larger and more ornamented than those of the Argentinian specimens referred to Rumohra adiantiformis , which are smaller and light brown.

Because there are many synonyms of R. adiantiformis in the Neotropical region ( Sundue et al., 2013; Ponce & Arana, 2016), and perhaps one of them could be applied to the new species described here, we reviewed the synonyms within R. adiantiformis from Neotropical Southern South America. Cavanilles (1802) described Tectaria calahuala Cav. (1802: 252) and Tectaria ferruginea Cav. (1802: 252) based on specimens from Buenos Aires ( Argentina) and Montevideo ( Uruguay), respectively. Both type specimens, Tectaria calahuala (Buenos Aires, 1801, L. Née 621, holotype MA 476410) and Tectaria ferruginea (Montevideo, L. Née s.n., holotype MA 476421), were studied under stereoscopic microscope, and spore samples were analysed with LM and SEM. Morphologically and palynologically, these specimens fit with the concept of Rumohra adiantiformis by Sundue et al. (2013). Bauret et al. (2017) found this morphological defined R. adiantiformis to be most likely polyphyletic, but material from the Southern continental Chile and Argentina, including the Malvinas (Falkland) Islands, together with the Juan-Fernandez endemic R. berteroana , forms a clade with Australian, New Zealand and New Guinean material. These populations may be kept under the name R. adiantiformis ( Bauret et al., 2017) . To confirm this, further studies are currently underway, taking into account that these populations develop in a completely different biogeographical area, the Andean region (also known as Andean- Patagonian, Patagonian or Austral). This biogeographic region belongs to the Austral kingdom with relationships with south-eastern Australia, Tasmania, New Zealand, New Guinea and New Caledonia ( Morrone, 2018; Arana et al., 2021). The Patagonian lineage ( Bauret et al. 2017), together with R. adiantiformis from Australasia, show a typical circumantarctic distribution.

Rumohra ponceana has a very restricted distribution area, growing in Southern Buenos Aires Province exclusively in the Tandilia and Ventania Mountain Systems, which have Chacoan biogeographic affinities ( Arana et al., 2021). The nearest populations of Rumohra adiantiformis grow in riparian environments of the Delta del Parana district, which is located to the northeast and belongs to the Esteros del Iberá biogeographic province, with Parana biogeographic relationships ( Arana et al. 2021).

The Tandilia and Ventania Systems are considered as orographic islands ( Crisci et al. 2001; Kristensen & Frangi 1995), where the biodiversity is characterized by an elevated number of endemics of various lineages ( Arana et al., 2021) with several threats ( Kacoliris et al. 2013): Invasive woody plant species are transforming the grassland and homogenizing the landscape; also, the overgrazing by livestock and the urbanization of the area accentuate the degradation, fragmentation and isolation of grassland remnants in the mountains ( Márquez et al. 2019; Zalba & Villamil 2002).

Figures

FIGURE 1. Holotype of Rumohra ponceana, de la Sota 5283 (LP 082551).

FIGURE 2. Rumohra ponceana.—A: general habit showing lamina architecture; B: last segment, abaxial view with sori.—Drawn from holotype, LP 082551, by H. Mussolini.

FIGURE 3. Rumohra ponceana. Morphology of the scales. A–E. Rhizome scales. A. Scale with entire margin. B. Scale with denticulate margin. C. Detail of denticulate margin. D–E. Glandular hairs in scales of specimens from different localities. F–K. Petiole Scales. F. Scale with entire margin. G. Scale with denticulate margin and glandular hairs. H. Glandular hair in detail (arrow). I–K. A whole scale with denticulate margin. I. Auriculed base (arrowheads). J. Middle zone. K.Apex. L–Q. Leaf scales. L–N. Different scales from the rachis. O–Q. Different scales from the lamina. A–B, D, F–H from de la Sota 5283; C, E, I–K, P–Q from Proyecto Ventania 1035 and Delucchi 2950; M–O from de la Sota 5291.

FIGURE 4. Morphology of the spores. A–D Rumohra ponceana. A. LM micrograph of a spore in equatorial view. Tuberculate perispore is evident. B–D. SEM micrographs. Tubercles of different sizes and shapes are observed over the entire surface. B. Spore in equatorial view. C. Spore in distal view. D. Spore in proximal view. Tubercles on the laesurae are observed (arrows). E–H. Rumohra adiantiformis. E. LM micrograph of a spore in distal view. Folded perispore with scattered tubercles. F-H. SEM micrographs. F. Spore in distal view with folded perispore with irregular tubercles. G. Spore in equatorial view. Tubercles in distal pole are evident. H. Spore in proximal view. Rugulated perispore and a straight and tenuimarginate laesura are evident (arrow).A from de la Sota 5291; B–D from de la Sota 5283 and Meza Torres et al. 315; F–H from Berrueta et al. 343.

FIGURE 5. Habitat of Rumohra ponceana. A. Buenos Aires, Tandil, Cerro Venado, 389 m a. s. l. B. Sunny rock crevices showing Rumohra ponceana populations. C. General aspect of Rumohra ponceana in more detail.All photographs by M. Luján Luna.