A new species of Blechnum L. (Blechnaceae, Polypodiopsida) from central-western Brazil, with an updated key to the species in the country

ABSTRACT

We describe a new species of Blechnum from Mato Grosso, Brazil: Blechnum rivulorum sp. nov. This new species was discovered as a result of visits to the herbaria BM, K, P, PR, and S, as part of the Reflora Project, by the first author. We also indicate its position in a new Blechnum phylogeny. Additionally, we confirm the occurrence of Blechnum meridense Klotzsch in Brazil and provide an updated key to all species of Blechnum in the country.

Keywords:
Blechnum; Blechnaceae; Polypodiopsida; ferns; pteridophytes; central-western Brazil; biodiversity; taxonomy

Introduction

Blechnaceae is a fern family with about 265 species (Gasper et al. 2016; PPG 1 2016), these characterized by monomorphic to dimorphic fronds, petioles with numerous vascular bundles forming a ring in cross section (Rothfels et al. 2012), sori linear with introrse indusia (rarely exindusiate), generally parallel and adjacent to midveins (Gasper et al. 2016; Tryon & Tryon 1982).

The family is organized in three subfamilies and 25 genera (Gasper et al. 2016; Molino et al. 2019), of which Blechnum L., with about 30 spp., is the third largest (Dittrich et al. 2015; PPG 1 2016). Blechnum in the restricted sense treated by us is restricted to the Neotropics and Africa, and can be recognized by its stoloniferous rhizomes, monomorphic to subdimorphic fronds, and finely denticulate pinna margins (Gasper et al. 2016). The genus was taxonomically investigated in the Neotropics by Murillo (1968) and Rolleri et al. (2012), and in Brazil it was studied by Dittrich et al. (2015), who ascribed 11 species to southern and southeastern Brazil, the richest area in the country. There are some recently described endemic species in northern and central-western Brazil (Dittrich et al. 2012). Altogether, 13 species of Blechnum are known from Brazil (Dittrich & Gasper 2022).

Even though many floras give a good account of Blechnum in many countries (e.g., Proctor 1985, for Jamaica; Mickel & Smith 2004, for Mexico; Ramos Giacosa 2016, for Argentina; Smith & Kessler 2018, for Bolivia), new species are still being discovered, and some species complexes (as Blechnum occidentale s.l.) need new study to avoid Linnean shortfalls (Hortal et al. 2015). Mato Grosso is not a particularly important area of endemism for ferns, but recently Matos & Vasco (2022) described an endemic species of Elaphoglossum from the state, Elaphoglossum mattogrossense. Aiming to contribute to BFG - Brazil Flora Group (BFG 2018) to achieve the Global Strategy for Plant Conservation (GSPC) established by the Conference of Parties in 2002, we describe a new Blechnum species, confirm the record of Blechnum meridense Klotzsch for Brazil, and provide an updated key to all species in the country.

Material and methods

Morphology

Herbarium specimens were consulted at BM, CESJ, BHCB, HRCB, K, and S (herbarium codes follow Thiers 2022), as well as the Virtual Herbarium INCT/HVFF (https://specieslink.net/)

Molecular phylogeny

Our sample (Almeida 2635) was extracted with DNeasy Plant Mini Kit (Qiagen Inc.,Valencia, CA) using field-collected silica-gel-dried tissue. Amplification follows Gasper et al. (2017) with the same three genome regions and methods: rbcL (Haufler & Ranker 1995), rps4-trnS (Nadot et al. 1995; Smith & Cranfill 2002), and trnL-trnF (Taberlet et al. 1991; Trewick et al. 2002). PCR products were sequenced on High Throughput Genomics (http://www.htseq.org). We used the same sequences from Gasper et al. (2017) for Blechnum (17 taxa), plus Cranfillia (two taxa) and Austroblechnum (two taxa) as outgroups. The sequences were aligned with MUSCLE (Edgar 2004) using MEGA XI (Tamura et al. 2021), with manual adjustments when necessary and no ambiguous areas excluded. We performed a maximum likelihood (ML) in IQ-TREE server with default settings (Trifinopoulos et al. 2016). GenBank accession number rbcL (ON645313), rps4-trnS (ON645314), and trnL-trnF (ON645315).

Results

Blechnum rivulorum V.A.O. Dittrich & Salino, sp. nov. (Figs. 1, 2, 3) - TYPE: BRAZIL. Mato Grosso: Chapada dos Guimarães, Parque Nacional da Chapada dos Guimarães, trilha para o Véu da Noiva, 15°24'21"S, 55°50'10"W, 28 Feb 2011, T.E. Almeida et al. 2635 (holotype, BHCB; isotype, CESJ).

Figure 1
Blechnum rivulorum. A. Habit. B. Rhizome scales. C. Proximal pinna pair, showing venation. D. Median pinna pair. All from Pivetta 1497, a paratype (HRCB). Drawn by Samyra Gomes Furtado.

Figure 2
Spores of Blechnum rivulorum, from T.E. Almeida et al. 2635 (BHCB).

Figure 3
Photos of Blechnum rivulorum in nature, taken at Cachoeira do Relógio, border of Cuiabá and Santo Antônio do Leverger municipalities, Chapada dos Guimarães, Mato Grosso, Brazil (15°36'55.7"S, 55°28'45.8"W, 695 m). A. Habit. B. Fronds. C. Sori. D. Stipes. (Photos: V.A.O. Dittrich).

Plants epipetric; rhizomes erect, stoloniferous, the scales narrowly triangular, light to dark tan, concolorous, 1 × 0.2 mm at the base, margins entire or with few teeth; fronds monomorphic, 2.9-13.4 cm long; stipes filiform, paleaceous to almost black, 1.1-3.9 cm long, 0.3-0.4 mm diam. at the base with scales similar to those on the rhizome; blades linear, elliptic, ovate or oblanceolate, 1.9-8.8 × 0.5-1.8 cm, glabrous, papyraceous, pinnatisect (sometimes pinnate between the two proximal pinnae pairs), at the apex with a more or less caudate segment 1-4 cm long, lobed at the base or not, longer than lateral pinnae, or rarely subconform, abruptly reduced toward the base to a vestigial pinna pair or to an ordinary, smaller pinna, or not reduced at all; rachises glabrous or with scattered multicellular hairs on both faces; pinnae (1)3-7(11) pairs, 0.4-1.2 × 0.3-0.7 cm at the base, sometimes broader than long, slightly (mainly the basal ones) to strongly (mainly the middle and distal ones) ascending, generally sursumcurrent (all ordinary pinnae and auricles) or just adnate to rachis (auricles), triangular, margins finely denticulate, apex rounded, acute, or mucronate; veins free, simple to bifurcate, small pinnae of small specimens sometimes lacking a clear midrib (pinnae dimidiate), with clavate ends before reaching the margin. Spores monolete, 48-55 μm in equatorial view, granulate or rugulate with low folds.

Comments: Blechnum rivulorum is closely related to Blechnum polypodioides Raddi and B. asplenioides Sw. From the first it can be distinguished by the pinnae more strongly ascending, generally more than 45° (when ascending, in B. polypodioides, generally not more than 30°), distinct spores (perispore with low folds vs. perispore without folds in B. polypodioides) and stipe diameter (filiform, not more than 0.4 mm diam. vs. stouter stipes 0.9-1.1 mm diam. in B. polypodioides). From B. asplenioides it can be distinguished by the blades abruptly reduced proximally to a vestigial pinna pair or to a smaller pinna (gradually reduced proximally in B. asplenioides, generally to semicircular lobes), by the sinuses (wide in B. rivulorum vs. narrow in B. asplenioides) and by the linear, elliptic or oblanceolate blades (vs. linear-lanceolate in B. asplenioides). Furthermore, B. asplenioides tends to be a more robust plant (fronds 5.7-30 cm long vs. 2.9-13.4 cm long in B. rivulorum) with more pinnae (6-32 pairs) than B. rivulorum ((1)3-7(11) pairs).

Blechnum rivulorum forms a clade with Blechnum asplenioides and Blechnum polypodioides in the maximum likelihood analysis, with high support, in the Blechnum polypodioides clade (Fig. 4, indicated by an asterisk). Despite our goal was not to provide a new phylogeny of Blechnum s.s., we can identify B. rivulorum affinities. This is a well-supported clade composed by small plants (when compared to the Blechnum occidentale clade), with areolate-veined species (Dittrich et al. 2012) as sister to Blechnum rivulorum+asplenioides+polypodioides.

Figure 4
Maximum likelihood phylogeny of Blechnum L. based on three chloroplast regions (rbcL, rps4, trnL-trnF). Maximum likelihood bootstrap support values are indicated near nodes; Blechnum rivulorum is shown by an arrow.

At least one specimen has some dimidiate pinnae. Those pinnae are very small in this specimen, but this may be result of their size. Fertile dimidiate pinnae have sori not following any vein, but instead at the base of a few veins. Variation in frond shape is striking, even at the same individual (e.g., Salino 380, UEC).

This species grows on sandstone rocks, generally along rivers or close to them. Their habitat and morphology suggest that they may be rheophytes. The species name (latin rivulorum = from the rivers) indicates their preferred habitat.

Additional specimens examined (paratypes): Brazil, Mato Grosso: Barra do Garças, 9 km NE of Barra do Garças, 450-500 m, 5 May 1973, W.R. Anderson 9761 (K, P, UB - photo, US - photo); idem, ca. 5 km N of Barra do Garças, at base of south face of mountain, 500 m, 24 Feb 1982, W.R. Anderson 12441 (MBM, - photo, NY - photo); Chapada dos Guimarães, perto do arroio que forma o Véu da Noiva, 15 Jul 1991, J. Pivetta 1497 (HRCB, SJRP - photo); ibidem, 16 Feb 1988, A. Salino 380 (UEC - photo); ibidem, Rio Coxipozinho, 28 Jan 1989, R.F. Novelino 613 (CESJ); ibidem, Salgadeira, 28 Jan 1989, R.F. Novelino 610 (CESJ); Cuiabá, Rodovia MT-351, Balneário Salgadeira, próximo ao limite com o município de Chapada dos Guimarães, 17 Apr 2003, F.P.F. Athayde & D.F. Peralta 1211 (HBRA - photo); idem, Parque Nacional da Chapada dos Guimarães, Trilha para a base da cachoeira Véu de Noiva, parte alta da trilha, 15°24'21"S, 55°50'11"W, 553 m, 15 Jul 2018, B. Canestraro 1252 (CESJ).

Updated key to Blechnum in Brazil

1. Fronds subdimorphic, the fertile ones slightly contracted ……………………………… 2

- Fronds monomorphic, the fertile ones not contracted …………………………………… 4

2. Veins partially anastomosing ……………………………………………..…. B. heringeri

- Veins free ………………………………………………………………………………… 3

3. Sterile blades at most 6.1 cm wide; sori continuous, rarely some interrupted; proximal pinnae of sterile fronds gradually reduced, 2.5-5 × shorter than the longest pinnae ................ B. auriculatum

- Sterile blades at least 8 cm wide; sori generally, at least partially, interrupted; proximal pinnae of sterile fronds slightly reduced, 1.2-2(3) × shorter than the longest pinnae ……………………... B. × leopoldense

4. Veins partially anastomosing …………………………………………………………… 5

- Veins free .........………………………………………………………………………...… 6

5. Pinnae 1-2 pairs; blades truncate at base ………………………………….. B. areolatum

- Pinnae (4-)5-7(-11) pairs; base of blades with one to three reduced pinnae ………………………………………………………………………………. B. longipilosum

6. Blades simple, entire ………………………………………………………….. B. lanceola

- Blades pinnatisect or pinnate …………………………………………………………… 7

7. Blades gradually reduced to semicircular lobes or to auricles at the base …………….. 8

- Blades not reduced or reduced at the base, if so never gradually reduced to semicircular lobes

or to auricles ……………………………………………………………………………… 9

8. Median pinnae deltate, strongly ascending; basal pinnae semicircular .......... B. asplenioides

- Median pinnae narrowly triangular, patent or slightly ascending; basal pinnae surcurrent .................................................................................................................... B. polypodioides

9. Lamina apex a conform or subconform terminal pinna, 1.1-3.2 times longer than the longest lateral pinna ……………………………………………………………………………… 10

- Lamina apex pinnatifid or with a more or less caudate segment, not conform or subconform .............................................................................................................................................. 13

10. Lamina apex subconform; distal pinnae surcurrent …………………………………….. 11

- Lamina apex conform; distal pinnae not surcurrent ………………………………………. 12

11. Proximal pinna pair free from the rachis ………………………………....... B. × caudatum

- Proximal pinna pair adnate to the rachis ………………………………..……… B. rivulorum

12. Fertile terminal pinnae cuneate and symmetric at the base, very rarely lobed; pinna pairs 2(3) ……………………………………………………………………………………. B. meridense

- Fertile terminal pinnae lobed and/or asymmetric at the base; pinna pairs (2)3-5(-8); ……………………………………………………………………………………….. B. gracile

13. Acroscopic side of the proximal pair of pinnae partially or completely adnate to the rachis ..14

- Acroscopic side of the proximal pair of pinnae totally free from the rachis ………………….. 17

14. Basiscopic side of the proximal pair of pinnae totally adnate to the rachis ………………... 15

- Basiscopic side of the proximal pair of pinnae completely or partially free from the rachis …. 16

15. Medial pinnae ascending, generally not more than 30°; stipes 0.9-1.1 mm diam. …………………………………………………………………………………… B. polypodioides

- Medial pinnae strongly ascending, generally more than 45°; stipes filiform, less than 0.4 mm diam. …………………………………………………………………………………. B. rivulorum

16. Hairs generally abundant on rachis and blade (at the margins, on or between veins, at both sides) ……………………………………………………………………………...… B. laevigatum

- Hairs, when present, only on rachis, rarely on veins, never at the margins or between veins ………………………………………………………………………………. B. austrobrasilianum

17. Basal pinnae proximally without auricles at the acroscopic side ……................ B. occidentale

- Basal pinnae proximally auriculate acroscopically ............................................. B. × leopoldense

New record for Brazil:

Blechnum meridense Klotzsch. BRAZIL: Rio de Janeiro, Corcovado, 1894, Herter s.n (S). According to Rolleri et al. (2012), this species was previously recorded in Brazil. They cite the voucher Albricht 165 (LP) and state that the specimen on the left is B. meridense. Unfortunately, there is no photo of it, and we were unable to see any image (according to Laura Iharlegui from LP, pers. com., the specimen Albricht 165 could not be found in the collection). This is the only specimen seen by the authors in Brazil, and since this specimen was collected more than 120 years ago amid an urban area that is one of the main centers of research in Botany in the country, we believe it is probably locally extinct.

Acknowledgments

The senior author acknowledges CNPq/Reflora program for financial support and the fern curator at K for loan specimens of Blechnaceae. All authors acknowledge Samyra Gomes Furtado for the drawing. ALG and AS thanks CNPq for the productivity grants (311303/2020-0 and 313981/2020-5, respectively).

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Publication Dates

• Publication in this collection
  21 Oct 2022
• Date of issue
  2022

History

• Received
  01 June 2022
• Accepted
  26 Sept 2022