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A new saxicolous species of Acisanthera (Melastomataceae: Marcetieae) from Chapada dos Guimarães National Park, Mato Grosso, Brazil

ABSTRACT

Acisanthera saxatilis is described, illustrated, and compared with putative relatives. The first specimen of this new species was collected 119 years ago by Oskar Andersson Gustaf Malme during his "second expedition Regnelliana". Acisanthera saxatilis is a little collected species apparently endemic to rocky sandstone formations in Chapada dos Guimarães, Mato Grosso state, Brazil. It differs from similar species by its perennial habit, lignotubers, isomorphic to slightly subisomorphic androecium, stamens positioned in a circle around the style during anthesis, antesepalous stamens with short connectives, small inconspicuous staminal appendages, and purple anthers. Photos of living specimens, a distribution map, scanning electron photographs of seeds and leaves, a preliminary conservation status assessment, as well as comments on vascular plant endemism at the Chapada dos Guimarães are provided.

Keywords:
Acisanthera; Brazil; Cerrado; Chapada dos Guimarães; Mato Grosso; neotropical region; endemism; endangered species.

Introduction

Acisanthera (Melastomataceae) is a neotropical genus comprising seven species of annual or perennial herbs to subshrubs (Kriebel 2008Kriebel R. 2008. Systematics and biogeography of the neotropical genus Acisanthera (Melastomataceae). MSc thesis, San Francisco State University, San Francisco.; Rocha et al. 2018Rocha MJR, Guimarães PJF, Michelangeli FA, Batista JAN. 2018. Taxonomy of Marcetieae: a new Neotropical tribe of Melastomataceae. International Journal of Plant Sciences 179: 50-74. ). This genus has a complex taxonomic history and remarkable morphological variation (Kriebel 2008Kriebel R. 2008. Systematics and biogeography of the neotropical genus Acisanthera (Melastomataceae). MSc thesis, San Francisco State University, San Francisco.; Guimarães et al. 2017Guimarães PJF, Silva MFO, Rocha MJ. 2017. Nomenclator botanicus for Acisanthera (Melastomataceae: Marcetia alliance). Brittonia 69: 231-240. ). About 18 species were traditionally recognized in a broadly circumscribed Acisanthera. Recent analyses based on both morphological and molecular data sets support the re-circumscription of Acisanthera s.l. into four genera, i.e. Rostranthera, Dicrananthera, Noterophila, and Acisanthera s.s. (Rocha et al. 2016Rocha MJR, Batista JAN, Guimarães PJF, Michelangeli FA. 2016. Phylogenetic relationships in the Marcetia alliance (Melastomeae, Melastomataceae) and implications for generic circumscription. Botanical Journal of the Linnean Society 181: 585-609. , 2018Rocha MJR, Guimarães PJF, Michelangeli FA, Batista JAN. 2018. Taxonomy of Marcetieae: a new Neotropical tribe of Melastomataceae. International Journal of Plant Sciences 179: 50-74. ). In this context, Acisanthera s.s. was re-defined to include only species with 5-merous flowers and 3-locular ovaries (Rocha et al. 2018Rocha MJR, Guimarães PJF, Michelangeli FA, Batista JAN. 2018. Taxonomy of Marcetieae: a new Neotropical tribe of Melastomataceae. International Journal of Plant Sciences 179: 50-74. ), matching Acisanthera sect. Acisanthera as previously delimited by Cogniaux (1885Cogniaux A. 1885. Acisanthera. In: Martius CFP, Eichler AG, Urban M (eds.) Flora Brasiliensis 14, part. III. Monachii, Fleischer. p. 205-226.). Species of Acisanthera s.s. occur from Cuba south to Argentina. In the southern portion of their distributional ranges they are best represented in the mountainous regions of southern Brazil, where A. variabilis, A. alsinaefolia and A. uniflora are found (Kriebel 2008Kriebel R. 2008. Systematics and biogeography of the neotropical genus Acisanthera (Melastomataceae). MSc thesis, San Francisco State University, San Francisco.; Flora do Brasil 2020Flora do Brasil 2020. 2021. Jardim Botânico do Rio de Janeiro. http://floradobrasil.jbrj.gov.br/. 12 Aug. 2021.
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).

The Chapada dos Guimarães is a region of flat-topped mountains located in the State of Mato Grosso, Midwestern Brazil (Ross 2014Ross JLS. 2014. Chapada dos Guimarães: Borda da Bacia do Paraná. Revista do Departamento de Geografia 28: 180-197. ). The summits of these flattened formations reach elevations between 600-800 m, consisting predominantly of Devonian and Cretaceous sandstones (Ross 2014Ross JLS. 2014. Chapada dos Guimarães: Borda da Bacia do Paraná. Revista do Departamento de Geografia 28: 180-197. ). These mountains, which are located in the Cerrado Domain, are home to a wide variety of habitats, such as savannas, gallery forests, grasslands and palm swamps (IBAMA 2009IBAMA. 2009. Plano de Manejo, Parque Nacional da Chapada dos Guimarães. Brasília, Ministério do Meio Ambiente.). Remarkable plant communities grow directly on the rocky sandstone outcrops, with a predominance of Vellozia, lichens and bromeliads (IBAMA 2009IBAMA. 2009. Plano de Manejo, Parque Nacional da Chapada dos Guimarães. Brasília, Ministério do Meio Ambiente.).

The Chapada dos Guimarães National Park was established in 1989. It comprises 32,630.70 ha and protects a significant part of the local biota (IBAMA 2009IBAMA. 2009. Plano de Manejo, Parque Nacional da Chapada dos Guimarães. Brasília, Ministério do Meio Ambiente.). The region currently delimited as the National Park was initially visited by several naturalists in the 19th century who gathered relevant ethnological and scientific information about the people, fauna, flora and famous landscapes (Barman 1971Barman RJ. 1971. The Forgotten Journey: Georg Heinrich Langsdorff and the Russian Imperial Scientific Expedition to Brazil. Terrae Incognitae 3: 67-96. ; Santos 2016Santos K. 2016. Brazilian plant specimens at the Regnellian herbarium: history and repatriation. Rodriguésia 67: 879-892. ). Initial botanical explorations were undertaken by Georg Heinrich Langsdorff (1774-1852) and Ludwig Riedel (1790-1861) in 1827, during the Russian Imperial Scientific Expedition to Brazil (Barman 1971Barman RJ. 1971. The Forgotten Journey: Georg Heinrich Langsdorff and the Russian Imperial Scientific Expedition to Brazil. Terrae Incognitae 3: 67-96. ), and by Oskar Andersson Gustaf Malme (1864-1937) during his expeditions to Mato Grosso in 1892-1894 and 1901-1904 (Santos 2016Santos K. 2016. Brazilian plant specimens at the Regnellian herbarium: history and repatriation. Rodriguésia 67: 879-892. ). Despite these early efforts, biological studies in the Chapada dos Guimarães are still scarce. Several endemic taxa have been described from the Chapada in recent years; these include invertebrates (Vilela et al. 2018Vilela DS, Guillermo-Ferreira R, Del-Claro K, Cordero-Rivera A. 2018. Argia angelae (Odonata: Zygoptera: Coenagrionidae) sp. nov. from Chapada dos Guimarães, Mato Grosso, Brazil. Zootaxa 4415: 549-560. ; Garcia & Urso-Guimarães 2018Garcia CA, Urso-Guimarães MV. 2018. Three new species of Lopesia Rübsaamen (Diptera: Cecidomyiidae) from Brazil. Florida Entomologist 101: 203-211. ), fish (Tagliacollo et al. 2011Tagliacollo VA, Britzke R, Silva GSC, Benine RC. 2011. Astyanax pirapuan: a new characid species from the Upper Rio Paraguay System, Mato Grosso, Central Brazil (Characiformes, Characidae). Zootaxa 2749: 40-46. ), a burrowing snake (Santos et al. 2018Santos FM, Entiauspe-Neto OM, Araújo JS, et al. 2018. A new species of burrowing snake (Serpentes: Dipsadidae: Apostolepis) from the state of Mato Grosso, Central-West region of Brazil. Zoologia 35: 1-10. ), lichens (Ferraro & Lücking 2003Ferraro LI, Lücking R. 2003. Gyalectidium aurelii (Ostropales: Gomphillaceae), a new foliicolous lichen from the State of Mato Grosso, Brazil. Acta Botanica Brasilica 17: 619-622 ), lycophytes (Valdespino et al. 2015Valdespino IA, Heringer G, Salino A, Góes-Neto LAA, Ceballos J. 2015. Seven new species of Selaginella subg. Stachygynandrum (Selaginellaceae) from Brazil and new synonyms for the genus. PhytoKeys 50: 61-99. ) and flowering plants (Rapini et al. 2010Rapini A, Koch I, Simões AO. 2010. Rauvolfia anomala, uma nova espécie de Apocynaceae da Chapada dos Guimarães, Mato Grosso, Brasil. Rodriguésia 61: 95-100. ; Leme et al. 2019Leme EMC, Forzza RC, Halbritter H, Ribeiro OBC. 2019. Contribution to the study of the genus Fosterella (Bromeliaceae: Pitcairnioideae) in Brazil. Phytotaxa 395: 137-167. ). Here, we describe a new species of Acisanthera that is apparently endemic to rocky sandstone walls of the Chapada dos Guimarães. The first specimen of this new species was collected 119 years ago by Oskar Andersson Gustaf Malme during his "second expedition Regnelliana" (Plantæ Itineris Regnelliani II.di), a productive exploration to the interior of Brazil, Argentina and Paraguay, which resulted in about 2,600 botanical collections (Santos 2016Santos K. 2016. Brazilian plant specimens at the Regnellian herbarium: history and repatriation. Rodriguésia 67: 879-892. ).

Materials and methods

This study was mostly based on collections from BHCB, CAS, CEPEC, HUEM, MBM, NY and US (acronyms follow Thiers 2021Thiers B. 2021. (continuously updated) Index Herbariorum: A global directory of public herbaria and associated staff. New York Botanical Garden’s Virtual Herbarium. http://sweetgum.nybg.org/science/ih/. 8 Aug. 2021.
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(continuously updated)). Specimens of all species mentioned in this study were examined, along with their protologues and online type images, available at the JSTOR Global Plants website (http://plants.jstor.org/). Comparative morphological characters of Acisanthera alsinaefolia (Mart. & Schrank ex DC.) Triana, A. erecta J. St.-Hil. and A. uniflora (Vahl) Gleason were obtained from treatments of Melastomataceae for the Floras of British Guiana (Gleason 1932Gleason HA. 1932. A synopsis of the Melastomataceae of British Guiana. Brittonia 1: 127-184.), Peru (Macbride 1941Macbride JF. 1941. Melastomataceae, Flora of Peru. Publications of the Field Museum of Natural History, Botanical Series 13: 249-521.), Panama (Gleason 1958Gleason HA. 1958. Flora of Panama Part VII, Fasc. 3, Melastomataceae. Annals of the Missouri Botanical Garden 45: 203-304.), Venezuela (Wurdack 1973Wurdack JJ. 1973. Melastomataceae. In: Lasser T (ed.) Flora de Venezuela, vol. 8. Caracas, Edición Especial del Instituto Botánico, p. 1-819.), Venezuelan Guayana (Berry et al. 2001Berry PE, Gröger A, Holst BK, et al. 2001. Melastomataceae. In: Berry PE, Yatskievych K, Holst BK (eds.) Flora of the Venezuelan Guayana. Saint Louis, Missouri Botanical Garden Press. p. 263-528.), Mesoamerica Region (Almeda 2009Almeda F. 2009. Melastomataceae. In: Davidse G, Sousa SM, Knapp S, Chiang F (eds.) Flora Mesoamericana. Mexico City, Universidad Nacional Autonoma de Mexico. p. 164-338.), Brazil (Cogniaux 1885Cogniaux A. 1885. Acisanthera. In: Martius CFP, Eichler AG, Urban M (eds.) Flora Brasiliensis 14, part. III. Monachii, Fleischer. p. 205-226.), and from the recent treatment of Acisanthera in Flora do Brasil 2020 (Rocha et al. 2020Rocha MJR, Guimarães PJF, Kriebel R. 2020. Acisanthera in Flora do Brasil 2020. Jardim Botânico do Rio de Janeiro . http://floradobrasil.jbrj.gov.br/reflora/floradobrasil/FB9395/. 12 Aug. 2021.
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).

Scanning Electron Microscopy (SEM) studies used dried herbarium material. Leaf fragments and seeds were placed on aluminum stubs with carbon tape and covered with a 30 to 40 nm layer of gold; SEM photos were taken using a FEI Quanta 200 scanning electron microscope at the Universidade Estadual de Maringá, Brazil (COMCAP/UEM).

We used the GeoCAT online tool (Bachman et al. 2011Bachman S, Moat J, Hill AW, de la Torre J, Scott B. 2011. Supporting Red List threat assessments with GeoCAT: geospatial conservation assessment tool. In: Smith V, Penev L (eds.) e-Infrastructures for Data Publishing in Biodiversity Science. ZooKeys. p. 117-126. ) to estimate the Extent of Occurrence (EOO) and Area of Occupancy (AOO), based on coordinates obtained directly at the type locality and from specimen labels; these estimations and the recommendation for the conservation status follow IUCN guidelines and criteria (IUCN 2012IUCN. 2012. IUCN Red List categories and criteria. Version 3.1. Second edition. Gland and Cambridg, IUCN Press.; IUCN Standards and Petitions Committee 2019IUCN Standards and Petitions Subcommittee. 2019. Guidelines for using the IUCN Red List categories and criteria. Version 14. Prepared by the Standards and Petitions Committee. http://www.iucnredlist.org/documents/RedListGuidelines.pdf.
http://www.iucnredlist.org/documents/Red...
). The distribution map was prepared using QGIS 3.10 (QGIS Development Team 2021QGIS Development Team. 2021. QGIS Geographic information System. Open Source Geospatial Foundation Project. http://qgis.osgeo.org/. 1 May 2021.
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).

Results

Acisanthera saxatilis Almeda & R. Pacifico sp. nov.

Type: BRAZIL. Mato Grosso, Chapada dos Guimarães, Parque Nacional da Chapada dos Guimarães, Trilha para o Morro São Jerônimo, (-15.4405, -55.83825), elev. 704 m, 5 July 2018, fl., fr, R. Pacifico 416 (holotype: HUEM!; isotypes: CAS!, CEPEC!, K!, RB!). (Figs. 1-2, 3C and 4-5).

Figure 1
Acisanthera saxatilis. A. Habit. B. Leaf adaxial surface. C. Leaf abaxial surface. D. Detail of the internode. E. Flower in lateral view. F. Petal adaxial surface. G. Antesepalous stamen. H. Antepetalous stamen. I. Flowering hypanthium (petals and stamens removed). J. Capsule in cross section. K. Seed in lateral view. Drawn from Hatschbach et al. 36107 (US).

Figure 2
Acisanthera saxatilis. Photograph of paratype, O.A.G. Malme 3481 (S).

Figure 3
Habitat of Acisanthera saxatilis. A. Landscape at the Chapada dos Guimarães, Mato Grosso, Brazil, showing the Véu da Noiva Waterfall and a large sandstone rocky outcrop. B-C. Sandstone rocky outcrops on the trail to the Morro São Jerônimo, the type locality of A. saxatilis. The black arrow indicates one individual of A. saxatilis. D. Detail of a hole in a rocky sandsone outcrop on the trail to the Morro São Jerônimo, covered by lichens and accumulating organic matter, where individuals of A. saxatilis grow.

Figure 4
Photos of living individuals of Acisanthera saxatilis. A-B. Habit. C. Leaf. D. Floral bud with reflexed calyx lobes. E. Capsule enveloped by hypanthium and attached calyx lobes. F. Flower. G. Close-up photo of a flower. All photos taken from the type series, R. Pacifico 416 (CAS, CEPEC, HUEM, K, RB).

Figure 5
Scanning Electron Microscopy photos of Acisanthera saxatilis. A. Seed in lateral symmetrical plane view. B. Seed in raphal view showing raphal zone and hilum. C. Seed in anti-raphal view. D. Detail of the seed testa cells showing anticlinal boundaries and periclinal walls. E. A spherical gland on the leaf abaxial surface. F. Foveolate appearance of the leaf adaxial surface. G. Petiole with glandular trichomes. All photos taken from the holotype, R. Pacifico 416 (HUEM).

Acisanthera saxatilis may be recognized by its perennial habit, lignotubers (xylopodia) membranaceous leaves with sparse glandular trichomes on the adaxial surface, isomorphic to slightly subisomorphic androecium, stamens erect and positioned in a circle around the style (during anthesis), connectives of both antesepalous and antepetalous stamens measuring 0.2-0.3 mm long, inconspicuous ventral appendages divided in two lobes ca. 0.1 mm long, and purple anthers.

Well-branched perennial shrub with trailing or pendulous stems ca. 5-20 cm long perennating from a woody lignotuber with many old defoliated wiry branches persisting from previous years. Roots brownish ca. 10 mm long. Upper cauline internodes 4-15 mm long, quadrangular, with tenuous wings up to 0.1 mm wide, light green at the apex and becoming brown flushed with red towards the base (when fresh), glutinous, moderately beset with white glandular trichomes 0.2-0.4 mm long, the heads of the trichomes white when fresh, turning pale brown when dry. Older branches brown (when dry), subquadrangular, the bark peeling away with age. Leaves opposite, isomorphic in size and shape in each pair, membranaceous, light green (when fresh) turning pale green and brittle when dry; petioles 1.7-6 mm long, somewhat compressed to quadrangular, covered with glandular trichomes 0.2-0.4 mm long, blades 6-22 × 3-10 mm, ovate to elliptic, 3-nerved (tertiaries not evident), concolored, light green (when fresh) or pale green (when dry), apex acute, base attenuate, foveolate and glabrous to glabrescent with sparse glandular trichomes 0.2-0.4 mm long adaxially, smooth and sparsely covered with glandular trichomes 0.2-0.4 mm long and a few spherical glands abaxially, hypostomatic, the margin entire and ciliate with glandular trichomes 0.2-0.4 mm long. Inflorescences reduced to solitary ebracteolate flowers born on pedicels 3-3.8 mm long in terminal and axillary positions on uppermost branchlets. Flowers 5-merous and diplostemonous. Hypanthium (at anthesis) 3.0-3.2 × 2.2-2.9 mm, cupuliform to campanulate, 10-ridged, smooth, light green when fresh turning pale green or flushed with purple when dry, covered with glandular trichomes 0.2-0.4 mm long. Calyx tube inconspicuous, ca. 0.1 mm long. Calyx lobes 3-3.4 × 0.7-0.9 mm, reflexed at anthesis, narrowly oblong with an obtuse apex, terminating in an apical glandular trichome ca. 0.4 mm long, the indumentum like that of the hypanthium, the margin entire and ciliate with glandular trichomes 0.2-0.4 mm long, light green when fresh, pale green when dry. Petals 6.2-6.6 × 2.9-3.1 mm, elliptic, light purple with an intense flush of purple at the base, glabrous throughout, the margin entire with a few minute glandular trichomes 0.1 mm long at the apex, the apex obtuse. Stamens 10, isomorphic to slightly subisomorphic, erect and positioned in a circle around the style (during anthesis): filaments 2.7-3.3 mm long, glabrous, white, anthers 1.6-2.5 mm long, purple, oblong and incurved, erostrate, with a ventrally inclined apical pore, connective prolonged 0.2-0.3 mm, ventral appendages inconspicuous and divided into two short thickenings ca. 0.1 mm long. Ovary (at anthesis) ca. 2.5 × 2 mm, superior, subglobose, glabrous; style 6.3-7 mm long, terete, slightly incurved, white. Fruit a globose loculicidal capsule 3-3.7 × 3-3.5 mm (when mature), 3-locular, glabrous, on pedicels 2.5-3.5 mm long, enveloped by the thin-walled hypanthium and persistent calyx lobes, then tardily rupturing and flaking away with age. Seeds subcochleate, beige to rusty brown, 0.5-0.6 × ca. 0.2 mm; the testa foveolate, raphal zone nearly circular, ca. 40 % the length of the seed.

Recognition-Acisanthera saxatilis is somewhat similar to A. erecta and A. uniflora in leaf shape, indumentum, and in having solitary flowers. Acisanthera saxatilis consistently differs from both species by its perennial habit, production of lignotubers, isomorphic to slightly subisomorphic androecium (vs. conspicuously dimorphic in the compared species), stamens positioned in a circle around the style during anthesis (vs. forming a cluster at one side of the flower), antesepalous stamens with shorter connectives 0.2-0.3 mm long. (vs. 1-2.5 mm long in the compared species), inconspicuous appendages ca. 0.1 mm long. (vs. conspicuous, usually 0.5-1 mm long) and all anthers purple (vs. usually bicolored, purple and cream). Comparative morphological characters among the species of Acisanthera reported for Brazil are provided in Tab. 1.

Table 1
Comparative morphological features among the four species of Acisanthera reported for Brazil.

Etymology-The specific epithet, saxatilis, which means living among rocks, highlights the habitat preference of this species on exposed rocky outcrops of the Chapada dos Guimarães.

Distribution, habitat and phenology-Acisanthera saxatilis is probably endemic to the Chapada dos Guimarães, Mato Grosso, Brazil (Fig. 6). It grows on shaded rocky sandstone outcrops, crevices and in round holes in these rocks, which accumulate organic material and may be externally covered with lichens and bryophytes (Fig. 3B-D), at elevations of about 676-704 m. It was collected flowering in February, March, June and July, and fruiting in February, June and July. According to specimen labels, its habitat is shared with the endemic bromeliad Fosterella lilliputiana, two rupicolous Gesneriaceae, i.e. Mandirola sp. and Goyazea petraea, and at least two species of ferns, i.e. Cheilanthes pohliana, Anemia sp., and one Lycophyte, Selaginella sp.; all of these taxa were collected on 13 February 1975 at the same sandstone rocky outcrops, during an expedition led by Gerdt Guenter Hatschbach (G. Hatschbach et al. 36107, 36109, 36110, 36111, 36112, 36113, 36114).

Figure 6
Distribution of Acisanthera saxatilis. A. South America with Mato Grosso State highlighted in black. B. Mato Grosso state with Chapada dos Guimarães municipality highlighted in black. C. Chapada dos Guimarães region showing the boundaries of the municipality (outlined in pink) and the National Park (outlined in blue), and the distribution of A. saxatilis. D. Trail to the Morro São Jerônimo in 3D view with the collection localities (white circles) of A. saxatilis.

Conservation-All collections of A. saxatilis with geographic coordinates came from the same locality (Fig. 6D). The type series (R. Pacifico 416), was obtained from a population of about 15 individuals. Using GeoCAT we estimated the EOO and AOO of A. saxatilis to be 0.001 km2 and 4 km2, respectively. If criterion B of IUCN (2012)IUCN. 2012. IUCN Red List categories and criteria. Version 3.1. Second edition. Gland and Cambridg, IUCN Press. and IUCN Standards and petitions subcommittee (2019)IUCN Standards and Petitions Subcommittee. 2019. Guidelines for using the IUCN Red List categories and criteria. Version 14. Prepared by the Standards and Petitions Committee. http://www.iucnredlist.org/documents/RedListGuidelines.pdf.
http://www.iucnredlist.org/documents/Red...
is applied, we suspect that a conservation status of Critically Endangered (CR) would be assigned to A. saxatilis: B2ab(iii). According to IBAMA (2009)IBAMA. 2009. Plano de Manejo, Parque Nacional da Chapada dos Guimarães. Brasília, Ministério do Meio Ambiente., the main threats to the vegetation of the Chapada dos Guimarães are: human-caused fires, human occupation, illegal logging, extraction of plants by locals, habitat degradation by cattle, unregulated tourism, and invasive alien species.

Additional specimens examined-Brazil. Mato Grosso: Chapada dos Guimarães, 13 February 1975, fl., fr., G. Hatschbach 36107 et al. (MBM, NY!, US!); ad Cascata grande, pr. Buriti (Chapada dos Guimarães), 8 June 1903, fl., fr., O.A.G. Malme 3481 (S!); Chapada dos Guimarães, Parque Nacional da Chapada dos Guimarães, trilha para o Morro São Gerônimo, (-15.439722, -55.83833); 676 m; 3 March 2011, fl., N. F. O. Mota 2121 et al. (BHCB!, MBM!).

Discussion

Morphological variation is complex in Acisanthera s.s. and presents challenges for species delimitations (Kriebel 2008Kriebel R. 2008. Systematics and biogeography of the neotropical genus Acisanthera (Melastomataceae). MSc thesis, San Francisco State University, San Francisco.). Here, we treat A. saxatilis as a distinct species largely based on stamen shape and size, together with its perennial habit, production of lignotubers, peculiar habitat on rocky sandstone outcrops, and limited distribution on the Chapada dos Guimarães, Brazil. We know of no other species of Acisanthera with developed lignotubers but they are known in species of Microlicia (Microlicieae), especially those in the Lavoisiera clade (Martins & Almeda 2017Martins AB, Almeda F. 2017. A monograph of the Brazilian endemic genus Lavoisiera (Melastomataceae: Microlicieae). Phytotaxa 315: 1-194. ), and in Chaetogastra (Melastomateae) (Meyer et al. 2021Meyer FS, Reginato M, Smidt EC, Gómez JRS, Michelangeli FA, Goldenberg R. 2021. Phylogenetic relationships in Brachyotum and allies (Melastomataceae, Melastomateae): a reassessment of the limits of the genera. Botanical Journal of the Linnean Society 197: 170-189.). These woody subterranean structures are common in species of the Cerrado and other neotropical savannas (Sarmiento 1985Sarmiento G, Goldstein G, Meinzer F. 1985. Adaptive strategies of woody species in Neotropical savannas. Biological Reviews 60: 315-355. ). They serve as an organ that buffers plants against extremes of water loss, temporal mineral deficiency, and also provide protection against fires (Gottsberger & Silberbauer-Gottsberger 2006Gottsberger G, Silberbauer-Gottsberger I. 2006. Life in the cerrado: A South American tropical seasonal vegetation. Vol. 1. Ulm, Germany, Reta Verlag.). The positioning of the stamens in a circle around the style (during anthesis), the reduced ventral connectives and staminal appendages, and the anthers of both cycles of stamens similar in color are other apparent synapomorphies of A. saxatilis.

Acisanthera saxatilis seems to occur only on the Chapada dos Guimarães. Currently, it is the only species of the genus endemic to Brazil. The compared species of Acisanthera have never been collected at the Chapada dos Guimarães, making sympatric occurrence improbable. Acisanthera uniflora is widely distributed in South and Central America (Kriebel 2008Kriebel R. 2008. Systematics and biogeography of the neotropical genus Acisanthera (Melastomataceae). MSc thesis, San Francisco State University, San Francisco.) and was cited in relevant treatments of Neotropical Melastomataceae such as the floras of Mesoamerica (Almeda 2009Almeda F. 2009. Melastomataceae. In: Davidse G, Sousa SM, Knapp S, Chiang F (eds.) Flora Mesoamericana. Mexico City, Universidad Nacional Autonoma de Mexico. p. 164-338.), Panama (Gleason 1958Gleason HA. 1958. Flora of Panama Part VII, Fasc. 3, Melastomataceae. Annals of the Missouri Botanical Garden 45: 203-304.), Venezuela (Wurdack 1973Wurdack JJ. 1973. Melastomataceae. In: Lasser T (ed.) Flora de Venezuela, vol. 8. Caracas, Edición Especial del Instituto Botánico, p. 1-819.), Venezuelan Guayana (Berry et al. 2001Berry PE, Gröger A, Holst BK, et al. 2001. Melastomataceae. In: Berry PE, Yatskievych K, Holst BK (eds.) Flora of the Venezuelan Guayana. Saint Louis, Missouri Botanical Garden Press. p. 263-528.), and Brazil (Cogniaux 1885Cogniaux A. 1885. Acisanthera. In: Martius CFP, Eichler AG, Urban M (eds.) Flora Brasiliensis 14, part. III. Monachii, Fleischer. p. 205-226.; Rocha et al. 2020Rocha MJR, Guimarães PJF, Kriebel R. 2020. Acisanthera in Flora do Brasil 2020. Jardim Botânico do Rio de Janeiro . http://floradobrasil.jbrj.gov.br/reflora/floradobrasil/FB9395/. 12 Aug. 2021.
http://floradobrasil.jbrj.gov.br/reflora...
). Acisanthera erecta is largely restricted to northern South America and Central America (Kriebel 2008Kriebel R. 2008. Systematics and biogeography of the neotropical genus Acisanthera (Melastomataceae). MSc thesis, San Francisco State University, San Francisco.), and was cited as A. quadrata in the floras for Peru (Macbride 1941Macbride JF. 1941. Melastomataceae, Flora of Peru. Publications of the Field Museum of Natural History, Botanical Series 13: 249-521.), Mesoamerica (Almeda 2009Almeda F. 2009. Melastomataceae. In: Davidse G, Sousa SM, Knapp S, Chiang F (eds.) Flora Mesoamericana. Mexico City, Universidad Nacional Autonoma de Mexico. p. 164-338.), Panama (Gleason 1958Gleason HA. 1958. Flora of Panama Part VII, Fasc. 3, Melastomataceae. Annals of the Missouri Botanical Garden 45: 203-304.), Venezuelan Guayana (Berry et al. 2001Berry PE, Gröger A, Holst BK, et al. 2001. Melastomataceae. In: Berry PE, Yatskievych K, Holst BK (eds.) Flora of the Venezuelan Guayana. Saint Louis, Missouri Botanical Garden Press. p. 263-528.) and British Guiana (Gleason 1932Gleason HA. 1932. A synopsis of the Melastomataceae of British Guiana. Brittonia 1: 127-184.); its occurrence in Brazil was not confirmed in a recent treatment of Acisanthera for this country (Rocha et al. 2020Rocha MJR, Guimarães PJF, Kriebel R. 2020. Acisanthera in Flora do Brasil 2020. Jardim Botânico do Rio de Janeiro . http://floradobrasil.jbrj.gov.br/reflora/floradobrasil/FB9395/. 12 Aug. 2021.
http://floradobrasil.jbrj.gov.br/reflora...
). A recent report of A. erecta (as A. quadrata) from Mato Grosso do Sul state by Romero et al. (2018Romero R, Versiane AFA, Guimarães PJF. 2018. Checklist das Melastomataceae do estado Mato Grosso do Sul. Iheringia, Série Botânica 73 (supl.): 273-276. ) needs confirmation.

The narrow endemism of A. saxatilis is unusual in a genus with predominantly widespread taxa. Its apparent restriction to sandstone substrates suggests that it may be an edaphic endemic. To our knowledge, there is no catalogue of edaphic endemics for Brazil’s vascular flora. Among Melastomataceae, many species of Microlicia have narrow distributions and are endemic to quartzitic soils on Cadeia do Espinhaço (Pacifico et al. 2020Pacifico R, Almeda F, Frota A, Fidanza K. 2020. Areas of endemism on Brazilian mountaintops revealed by taxonomically verified records of Microlicieae (Melastomataceae). Phytotaxa 450: 119-148. ); both Microlicia macedoi and Pterolepis haplostemona are endemic to serpentine in Goiás state (Reeves et al. 2007Reeves RD, Baker AJM, Becquer T, Echevarria G, Moranda ZJG. 2007. The flora and biogeochemistry of the ultramafic soils of Goiás state, Brazil. Plant and Soil 293: 107-119. ; Almeda & Martins 2015Almeda F, Martins AB. 2015. Pterolepis haplostemona (Melastomataceae): a new serpentine endemic from Goiás, Brazil. Phytotaxa 201: 233-238.), whereas Brasilianthus carajensis and Pleroma carajasense are endemic to ironstone outcrops (canga) in Pará state (Almeda et al. 2016Almeda F, Michelangeli FA, Viana PL. 2016. Brasilianthus (Melastomataceae), a new monotypic genus endemic to ironstone outcrops in the Brazilian Amazon. Phytotaxa 273: 269-282.; Rocha et al. 2017Rocha KC, Goldenberg R, Viana P, Meyer FS. 2017. Pleroma carajasense (Melastomataceae), a new species endemic to ironstone outcrops in the Brazilian Amazon. Phytotaxa 329: 233-242. ). Further investigations using molecular data and chromosome number determinations may provide useful insights into the origin and interspecific relationships of A. saxatilis.

At least 16 species of vascular plants are apparently endemic to the Chapada dos Guimarães, Mato Grosso: Alstroemeria chapadensis (Alstroemeriaceae), Nephradenia filipes (Apocynaceae), Hypenia micrantha (Lamiaceae), Didymopanax cephalanthus (Araliaceae), Cuphea cuiabensis (Lythraceae), Mascagnia aptera (Malpighiaceae), Piriqueta lourteigiae (Turneraceae), Vochysia petraea (Vochysiaceae), Mimosa bipennatula (Fabaceae) (CNCFlora 2012CNCFlora. 2012. Lista Vermelha da Flora Brasileira. Versão 2012.2. Centro Nacional de Conservação da Flora. http://cncflora.jbrj.gov.br/. 12 Aug. 2021.
http://cncflora.jbrj.gov.br/...
; Flora do Brasil 2020 2021Flora do Brasil 2020. 2021. Jardim Botânico do Rio de Janeiro. http://floradobrasil.jbrj.gov.br/. 12 Aug. 2021.
http://floradobrasil.jbrj.gov.br/...
), Borreria guimaraesensis (Rubiaceae) (Cabral & Bacigalupo 2004Cabral E, Bacigalupo N. 2004. Novelties in Borreria (Rubiaceae-Spermacoceae) from Brazil. Kew Bulletin 59: 277-284. ), Fleischmannia matogrossensis (Asteraceae) (Robinson 2015Robinson H. 2015. The genus Fleischmannia in Argentina, Bolivia, Brazil and Paraguay (Eupatorieae, Asteraceae). PhytoKeys 57: 61-92. ), Fosterella lilliputiana (Bromeliaceae) (Leme et al. 2019Leme EMC, Forzza RC, Halbritter H, Ribeiro OBC. 2019. Contribution to the study of the genus Fosterella (Bromeliaceae: Pitcairnioideae) in Brazil. Phytotaxa 395: 137-167. ), Rauvolfia anomala (Apocynaceae) (Rapini et al. 2010Rapini A, Koch I, Simões AO. 2010. Rauvolfia anomala, uma nova espécie de Apocynaceae da Chapada dos Guimarães, Mato Grosso, Brasil. Rodriguésia 61: 95-100. ), Selaginella saltuicola (Selaginellaceae) (Valdespino et al. 2015Valdespino IA, Heringer G, Salino A, Góes-Neto LAA, Ceballos J. 2015. Seven new species of Selaginella subg. Stachygynandrum (Selaginellaceae) from Brazil and new synonyms for the genus. PhytoKeys 50: 61-99. ), Syagrus guimaraesensis (Arecaceae) (Noblick et al. 2014Noblick L, Lorenzi H, Souza VC. 2014. Four new taxa of acaulescent Syagrus (Arecaceae) from Brazil. Phytotaxa 188: 1-13. ), and Acisanthera saxatilis. Several of these narrowly endemic species are considered threatened (CNCFlora 2012CNCFlora. 2012. Lista Vermelha da Flora Brasileira. Versão 2012.2. Centro Nacional de Conservação da Flora. http://cncflora.jbrj.gov.br/. 12 Aug. 2021.
http://cncflora.jbrj.gov.br/...
). In this context, the discovery of A. saxatilis emphasizes the importance of the Chapada dos Guimarães National Park as a critical area for the conservation of several Cerrado endemic lineages in Mato Grosso state, Brazil.

Acknowledgments

We thank Alan Chou for the line drawings, Maria José Reis da Rocha and one anonymous reviewer for their comments on an earlier version of this manuscript, the staff of BHCB, MBM and US for sending loans of specimens for this study, the Chapada dos Guimarães National Park staff for their assistance during fieldwork activities (license 63452-1). We also thank Diego Nunes da Silva who brought the earliest known collection of this new Acisanthera to our attention.

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Publication Dates

  • Publication in this collection
    02 May 2022
  • Date of issue
    2022

History

  • Received
    13 Sept 2021
  • Accepted
    20 Jan 2022
Sociedade Botânica do Brasil SCLN 307 - Bloco B - Sala 218 - Ed. Constrol Center Asa Norte CEP: 70746-520 Brasília/DF. - Alta Floresta - MT - Brazil
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