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Research Article
Hidden in the mountain: a new rare Syagrus (Arecaceae) with morphological novelties
expand article infoBruno Francisco Sant’Anna-Santos, Elaine Lopes Pereira Nunes§, Rafael Micheli, Dayana Maria Teodoro Francino|
‡ Federal University of Paraná, Curitiba, Brazil
§ National Coalition of Independent Scholars, Battleboro, United States of America
| Federal University of Vales do Jequitinhonha e Mucuri, Diamantina, Brazil
Open Access

Abstract

Background and aims – The Serra do Ambrósio is a mountain with a unique vegetation called carrasco. The carrasco is characterised by sandy soils of high granulometry and is home to rare species. During the current research on the Arecaceae flora of the Diamantina Plateau, a new Syagrus species was discovered, which is described here.

Material and methods – The morphology and anatomy are described based on field collections. The pinnae anatomy was analysed using LM (free-hand cross sections). The new species belongs to the Syagrus glaucescens complex, and an identification key and a distribution map were created.

Key resultsSyagrus harenae resembles S. glaucescens, but some characteristics easily differentiate it, such as the small size, lax pinnae, symmetric pinnae tips, ramenta scales, a scattered thin indumentum on the peduncle, inflorescences and fruits orangish-yellow, and pistil with indumentum. The new species also possesses flowers arranged in tetrads and pentads and is the first species of Syagrus showing two sepals, petals with imbricate tips, staminodes with anthers, and frequently lacks staminodial rings. The pinnae anatomy of the new species also resembles S. glaucescens, which indicates their relatedness. However, reliable differences in pinnae anatomy set the new species apart, such as the fibrous ring reaching the abaxial hypodermis and the large first adaxial fibre bundle near the margin. The new species is assessed as critically endangered.

ConclusionSyagrus harenae is the first endemic species of the genus described for the Serra do Ambrósio and possesses striking characteristics, such as the re-greening of the pistillate flowers and flowers arranged in tetrads and pentads. The type population corroborates the Diamantina Plateau and its disjunctions as one of the centres of diversity for Syagrus. The discovery of this new species reinforces the uniqueness of the local flora and its classification as a priority area for conservation.

Keywords

campo rupestre, carrasco, Espinhaço Range, Palmae, Serra do Ambrósio, taxonomy

Introduction

The Espinhaço Range in eastern Brazil was designated a biosphere reserve by UNESCO (UNESCO 2005). In its central-southern region, within Minas Gerais State, the Diamantina Plateau is notable for its high degree of endemism (Giulietti et al. 1997; Echternacht et al. 2011; Costa et al. 2016). The Diamantina Plateau consists of two discontinuous areas across the landscape (see Fig. 3; Echternacht et al. 2011). In the easternmost area, formed by the Serra Negra Formation (Fig. 1A–D), the Serra do Ambrósio mountain is a little-studied disjunction notorious for its unique environmental conditions and endemics (Meguro et al. 1994; Pirani et al. 1994; Costa et al. 2016, 2018). The Serra do Ambrósio features physiognomically diverse plant communities, including gallery forests at its base, campos rupestres at the summits, and the lesser-known carrasco vegetation in between (Meguro et al. 1994).

Figure 1. 

Distribution map of the Syagrus glaucescens species complex, maps of Serra Negra Formation (SN), and 3D map of Serra do Ambrósio mountain (SA). A. Location of SN, Diamantina Plateau, Syagrus harenae, Syagrus aristeae, Syagrus duartei, Syagrus evansiana, and Syagrus glaucescens. B. Relief and outline of the SN and localisation of the SA. C. Municipalities embedded in the SN. D. Relief of the SA and collection points of Splett 875 and the holotype of S. harenae. E. An endocarp (en) of S. harenae on the sandy soil of the carrasco.

The carrasco is a more or less dense shrubland that grows in whitish and coarse sand (Meguro et al. 1994). To the best of our knowledge, other carrascos occur only to the north of the Diamantina Plateau, namely Grão Mogol (Pirani et al. 1994). According to Echternacht et al. (2011), Grão Mogol belongs to the northern mountains complex, separated from the Diamantina Plateau by extensive lowlands and distinct edaphoclimatic conditions. Notwithstanding, the sandy soils of the carrascos in the Serra do Ambrósio mountain are unique in the Diamantina Plateau due to their larger particle size (Fig. 1E), and Syagrus glaucescens was first recorded there in 1985 (see Meguro et al. 1994).

The monophyletic genus Syagrus Mart. comprises thus far 70 species, with Central and Eastern Brazil being the centre of its distribution (Meerow et al. 2009; Noblick 2017a; 2018; Sant’Anna-Santos et al. 2023a, 2023b, 2023c). In general, in neotropical seasonally dry habitats, Syagrus stands out with dozens of small to moderate-sized species (Noblick 2017a; Soares and Guimarães 2019; Sant’Anna-Santos et al. 2023a, 2023b, 2023c). In these regions, highland environments with unique edaphoclimatic conditions are home to different microendemic species of Syagrus (Noblick and Lorenzi 2010; Noblick 2017a; Sant’Anna-Santos et al. 2023a). Many of those species remain unrecognised due to their morphological similarity, and are only unveiled by detailed studies on their morphology and pinnae anatomy (see Noblick and Lorenzi 2010; Noblick 2013, 2017b; Noblick et al. 2014; Firmo et al. 2021; Sant’Anna-Santos et al. 2023a, 2023b, 2023c).

Initially, plant anatomy played a unifying role for Syagrus (Glassman 1972, 1979). Nonetheless, it has recently successfully supported infrageneric and infraspecific taxonomic decisions (Noblick and Lorenzi 2010; Noblick 2013, 2017b; Noblick et al. 2014). In fact, pinnae anatomy study and familiarity with these plants’ habits have been essential to solving these puzzling complexes of Syagrus from dry habitats (Noblick and Lorenzi 2010; Noblick 2013). Furthermore, several areas have only a few or no fieldwork for Syagrus collection (see Reflora 2024; SpeciesLink Network 2024), making it plausible that unknown species are waiting to be described.

The Serra do Ambrósio mountain is one of these understudied areas, standing out by the record of two species from the Syagrus glaucescens complex: Syagrus evansiana Noblick and Syagrus glaucescens Glaz. ex Becc. (Pirani et al. 1994; Noblick 2017a; SpeciesLink Network 2024; Reflora 2024). Besides these two species, Syagrus duartei Glassman and the recently described Syagrus aristeae Sant’Anna-Santos (see Firmo et al. 2021; Sant’Anna-Santos et al. 2023c) compose the Syagrus glaucescens complex. Until now, only a few general flora surveys have been carried out in Serra do Ambrósio. Thus, no one with field experience had examined these palms’ habits before. Moreover, this mountain should be prioritised in vegetation studies, considering its geographical isolation and the peculiar carrascos, where rare endemics of diverse taxonomic groups were found (Meguro et al. 1994; Pirani et al. 1994; Costa et al. 2016, 2018).

In other disjunctions of the Diamantina Plateau, such as the Serra do Cabral massif, S. glaucescens and S. evansiana were also recorded (see Firmo et al. 2021). However, increased fieldwork and detailed morphological and pinnae anatomy studies revealed S. aristeae, the newest addition to this species complex. Therefore, this work is an effort to check other overlooked populations of small to moderate-sized Syagrus from isolated mountains in the vicinities of the Diamantina Plateau, previously identified as S. glaucescens and S. evansiana in herbaria. Here, we aim to test the hypothesis that this disjunct population from the Serra do Ambrósio mountain may be a fifth species of the Syagrus glaucescens complex, not yet brought to light by science. Upon confirmation, this new record will increase the diversity of endemic taxonomic groups for Serra do Ambrósio mountain, which is not protected by conservation units.

Material and methods

This study was based on field observations in carrasco areas at the base of the Serra do Ambrósio mountain, municipality of Itamarandiba, Minas Gerais State, Brazil. This study also includes information from the specific literature about the species of the Syagrus glaucescens complex (Glassman 1967, 1968, 1970, 1987; Henderson et al. 1995; Dransfield et al. 2008; Noblick 2009, 2017a, 2017b; Firmo et al. 2021; Sant’Anna-Santos et al. 2023c), herbaria (DIAM, RB, SP, SPF, HDCF, HEPH, HPL, MBM, MCMG, UPCB) and online databases (UB, ESA, NY, K, US, P, HUFU, CEN). Morphological and anatomical terminology follows Dransfield et al. (2008), Tomlinson et al. (2011), Noblick (2017a, 2017b), and Firmo et al. (2021). The circumscription adopted here for Syagrus is based on Noblick (2017a) and Sant’Anna-Santos et al. (2023a, 2023b, 2023c). For the Syagrus glaucescens species complex, we followed the circumscription adopted by Noblick (2017a), Firmo et al. (2021), and Sant’Anna-Santos (2023c).

Qualitative and quantitative morpho-biometric data and images were recorded in situ for the new species. Data were taken from 30 individuals of the new species randomly chosen. For the remaining species of the S. glaucescens complex (S. aristeae, S. duartei, S. evansiana, and S. glaucescens), the morphological and anatomical data were retrieved from the literature (Noblick 2017a, 2017b; Firmo et al. 2021; Sant’Anna-Santos et al. 2023c) and are shown in Tables 1 and 2. For S. glaucescens, presently considered the most closely allied species of the new species, a known population from Diamantina municipality was visited to record images and to show the habitat and distinctive morphological features that contrast with the new species in Fig. 10. Samples of flowers of the new species were collected in the field and immediately analysed while fresh, and also stored in ethyl alcohol for further stereomicroscopic analysis (Bioptika L60T) coupled with a CMOS 12mp PLUS camera.

Table 1.

Differences in morphology between S. harenae and S. aristeae, S. duartei, S. evansiana, and S. glaucescens.

Syagrus harenae Syagrus glaucescens Syagrus duartei Syagrus evansiana Syagrus aristeae
Plant size Small to moderately-size Moderately-sized Small to moderately-sized Small Small
Stem size 0.4–1.1(–1.4) m × 15–25 cm 0.5–4 m × (8–)10–12 cm 0–2 m × 8–12 cm acaulescent 0.1–0.15 m × 3–9 cm
Leaf vertical rows Distinct Distinct Distinct Indistinct Indistinct
Subterranean stem Prostrate Erect Prostrate Subterranean Subterranean
Pinnae Lax Congested Congested Lax Lax
Leaf rachis 95–167 cm (55–)62–118 cm 50–90 cm 21–92 94–145 cm
Pinnae number 63–79 (38–)59–79 44–64 18–48 38–67
Pinnae clusters 2–5 3–5 2–3(–4) 2–4(–5) 2–3(–4)
Ramentas Present Absent Present Absent Absent
Tomentum petiole and rachis Present Absent Absent Absent Absent
Leaves 8–15 5–15 6–12 3–11 3–6
Sheathing leaf base ca 10–28 cm long 42–52 cm long 20 cm long 10–20 cm long 13–23 cm long
Apical pinnae 8–12 × 0.2–0.4 cm 1.5–6 × 0.2–1.0 cm 6–9 × 0.2–0.8 cm 3–12 × 0.1–0.9 cm 7–18 × 0.6–1.0 cm
Prophyll length 11–16(–26) cm 18 cm 18–22 cm 6–16 cm 7–23 cm
Peduncle indumentum Scattered thin indumentum Glabrous Glabrous Glabrous Glabrous
Inflorescence Strongly pendulous Erect or slightly pendulous Erect or slightly pendulous Erect Erect
Inflorescence Branched Branched Branched Spicate or branched Spicate or branched
Flower arrangement Triads/Tetrads/Pentads Triads Triads Triads Triads
Staminate flower length at the apex 9–10 mm 8–12 mm 10–15 mm 8–10 mm 10–12.5 mm
Staminate flower length at the base 11.5–14 mm 14–17 mm 16–28 mm 8–10 mm 11.2–15.9 mm
Staminate flower colour Yellow Green to yellow Green to yellow Yellow Yellow
Stamen length 5.0–7.0 mm 6.0–8.5 mm 8–10.5 mm 4–5 mm 5.9–9.0 mm
Anther length 4.0–7.0 mm 5.0–7.5 mm 6–9.5 mm 3.5–4.0 mm 4.4–7.7 mm
Filament length 2.0–3.0 mm 1.0–2.0 mm 2.0 mm 1.0 mm 1.3–3.2 mm
Pistillode 0.8–1.0 mm Less than 1 mm Less than 0.5 mm Less than 1 mm 0.5–1.5 mm
Pistillate flowers length 13–17 mm 10–17 mm 17–25 mm 8–19 mm 12.1–16 mm
Number of sepals 2–4 3 3 3 3
Number of petals 3–4 3 3 3 3
Petals tips Imbricate tips Valvate tips, 1/3 to 4/5 the length of the petal Valvate tips, 1/2 the length of the petal Valvate tips, 2/5 to 1/2 the length of the petal Valvate tips, 2/5 to 1/2 the length of the petal
Pistil size 6–8 × 3–4 mm 6–9 × 4.0–6.0 mm 10 × 4.5 mm 10–11 × 3.5–4 mm 5.8–7.7 × 2.1–3.9 mm
Pistil indumentum Whitish indumentum on lower 1/3 Glabrous Glabrous or fine wax indumentum Lepidote indumentum from base to nearly the base of the stigmas Glabrous
Stigmas 3–4 mm 3–4 mm 6 mm 3–5 mm 2.8–3.4 mm
Staminodal ring Less than 0.5 mm 0.7–2 mm ca 0.8 mm 1–3 mm 1 mm
Fruit Ellipsoid to ovoid Ellipsoid Nearly globose Globose Nearly globose
Fruit sized 2.1–3.0 × 1.6–2.0 cm 2–3 × 1.6–2.5 cm 3.0–3.8 × 2.5–3.2cm 1.5–2.3 × 1.5–2.3 cm 1.7–2.5 × 1.1–1.9 cm
Fruit colour when mature Orange Brown Brown Yellowish brown Yellowish brown
Mesocarp 1–2 mm 1–2 mm 2–4 mm 1–2 mm 1.0–2.5 mm
Endocarp size 1.8–2.0 × 1.2–1.9cm 2–2.8 × 1.7–2.1 cm 3.0–3.5 × 2.8–3.0 cm 1.4–1.6 × 1.1–1.3 cm 1.3–1.8 × 1.1–1.4 cm
Endocarp thickness on the sides 2–3 mm (2–)3–4 mm 5–8 mm 1 mm 1 mm
Table 2.

Differences in pinnae anatomy between S. harenae and S. aristeae, S. duartei, S. evansiana, and S. glaucescens.

Syagrus harenae Syagrus glaucescens Syagrus duartei Syagrus evansiana Syagrus aristeae
Number of accessory vascular bundles around the main vascular system of the midrib 1 5 0 0 2
Number of collateral bundles in the vascular system of the midrib 4–5 4–5 4–5 1 3
Fibrous ring reaching the abaxial hypodermis Present Absent Absent Absent Present
Non-vascular fibre bundle rounded attached to the abaxial surface Present Absent Absent Absent Absent
Midrib format Triangular Truncate Truncate Triangular Truncate
Tiny fibres in the abaxial hypodermis Present Absent Absent Present Present
One adaxial vascular bundle near the margin Sometimes Absent Absent Absent Absent
Large first adaxial fibre bundle near the margin Present Absent Present Present Absent
Abaxial tertiary vascular bundles Present Present Present Absent Present
Hypodermal cells rounded Absent Absent Present Absent Absent
Small group of fibres around the fibrous ring of the midrib Present Present Absent Present Present

The distribution map showing all species of the S. glaucescens complex was plotted using QGIS v.3.22.4 (QGIS Development Team 2024) and assembled from the following data sources: states and municipalities (IBGE 2020); Serra Negra formation vector (Silva et al. 2020); elevation (Farr and Kobrick 2000); species and sites (data from the current study). The collection point of Mello-Silva et al. 7833 was not included in Serra Negra’s map as the information in the voucher did not indicate the exact coordinates, only the municipality (see SpeciesLink Network 2024: https://specieslink.net/rec/7/38799). The distribution data for S. aristeae, S. duartei, S. evansiana, and S. glaucescens were retrieved from Firmo et al. (2021). All these sites are confirmed collection areas for these species and were selected based on Noblick (2009, 2017a), Firmo et al. (2021), and Sant’Anna-Santos et al. (2023c). A 3D map was created using QGIS v.3.22.4 (QGIS Development Team 2024) and digital elevation models from the SRTM (Farr and Kobrick 2000). The models were visualised with a 20× vertical exaggeration using native QGIS plugins and additional add-ins in the software. To assess the conservation status of the new species according to IUCN guidelines and criteria (IUCN 2022), the GeoCAT tool (Bachman et al. 2011) was employed. Since the localities where the new species occurs are close to each other and could be destroyed by a single threatening event, they were considered a single location, according to IUCN (2022). We based the pinnae anatomical study on 15 samples – collected from the middle of the central pinnae – from herbarium specimens of our collections and specimens in the field, following Firmo et al. (2021). After rehydration (Meira and Martins 2003), freehand cross sections were directly mounted in water without staining and photographed under a light microscope (Bioptika B20+) coupled to a digital camera (CMOS 12mo PLUS). The pinnae anatomical data of S. aristeae, S. glaucescens, S. duartei, and S. evansiana was retrieved from Firmo et al. (2021) and compared with the new species in Table 2.

In order to create an identification key to distinguish the species of the S. glaucescens complex, the data obtained here were compared with Noblick (2009, 2017a) and Sant’Anna-Santos (2023c). Steps 1 and 2 of the key presented here were constructed to enable Syagrus harenae to be differentiated from the other species in the Syagrus glaucescens complex: Syagrus aristeae, S. duartei, S. evansiana, and S. glaucescens. Steps 3 and 4 were based on Sant’Anna-Santos (2023c: 11) for the differentiation of S. aristeae and S. evansiana and Noblick (2017a: 16) for the differentiation of S. duartei from S. glaucescens.

Taxonomic treatment

Syagrus harenae B.F.Sant’Anna-Santos, sp. nov.

Figs 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, Tables 1, 2

Type

BRAZIL – Minas Gerais • Itamarandiba, Vilarejo de Penha da França; 18°2’44.76”S, 43°4’45.02”W; 1000 m; 15 Feb. 2024; fl., fr.; Sant’Anna-Santos & Francino 406; holotype: DIAM; isotypes: UPCB, IBGE, HCF.

Figure 2. 

Syagrus harenae. A. Prostrated stem. B. Sheathing leaf arranged in 5 nearly vertical or slightly spiralled rows. C. Flowers arranged in tetrads. D. Sepals connate at the base. E. Flowers arranged in pentads. F. Fruits. G. Endocarp pores. A–G from Sant’Anna-Santos & Francino 406 (DIAM, holotype). Illustration by Gustavo Surlo.

Diagnosis

Syagrus harenae is similar to S. glaucescens Glaz. ex Beccari, from which it differs by lax pinnae on the leaf rachis (vs congested pinnae), apical pinnae size (8–12 × 0.2–0.4 vs 1.5–6 × 0.2–1.0), pinnae with symmetrical tip (vs asymmetrical); base of the stem not-angular (vs angular), brownish indumentum where pinnae are inserted on the lower leaf rachis (vs glabrous); prostrated stem (vs erect); sheathing leaf base length (10–28 cm vs 42–52 cm), lax sheathing leaf base (vs congested); inflorescence strongly pendulous (vs erect ou slightly pendulous); peduncle with scattered thin indumentum (vs glabrous); petal tips imbricate (vs valvate); pistil with whitish indumentum on lower 1/3 (vs glabrous), inconspicuous staminodial ring (vs conspicuous staminodal ring); fruit yellowish-orange when mature (vs brownish).

Description

Small to moderate-sized palm, solitary, 110–160(–250) cm tall. Stem 40–110(–140) × 15–25 cm, prostrate, with persistent leaf bases arranged in rows with indistinct internodes near the crown, non-angular stem base. Leaves pinnate number 8–15; sheathing leaf base ca 10–28 cm long; pseudopetiole 15–37 cm long; petiole 9–27 × 0.5–1.6 cm and 0.2–0.7 cm thick, rachis 95–167 cm long; abaxial side of petiole and rachis with brownish tomentum; pinnae medium to dark-green, discolourous, abaxial surface glaucous, linear, rigid-coriaceous with apex more or less symmetrical and long tapering, pinnae numbering 63–79 pairs, in clusters of 2–5, lax on leaf rachis, inserted in divergent planes over the rachis; pinnae with inconspicuous ramenta scales along the abaxial midrib (near the rachis) on young leaves; basal pinnae 27–36 × 0.4–0.6 cm, middle pinnae 17.5–30.5 × 1.7–2.3 cm, apical pinnae 8–12 × 0.2–0.4 cm. Inflorescences pendulous, spirally branched, prophyll 11–16(–26) × 1.3–2.5 cm; peduncular bract 56–72 cm long, inflated portion 25–31 × 5.2–7.5 cm, including a 1.0–1.4 cm beak, 6.4–8.5 cm perimeter, 2–3 mm thick, woody, sulcate, exterior glabrous; peduncle 30–41.5 cm long, 8–10 × 4–7 mm wide, with brownish scarce indumentum; inflorescence axis 19.5–24 cm long; rachis 1.5–13.3 cm long; rachillae 3–15, glabrous, yellow, 8.5–20 cm long at the apex, 12–17 cm long at the base; flowers arranged in triads, tetrads (with two central pistillate flowers, each flanked by a staminate flower) or pentads (with three central pistillate flowers flanked by two staminate flowers), staminate flowers with three sepals and three petals, and pistillate flowers with three sepals and three petals, two sepals and four petals, three sepals and four petals. Staminate flowers 9–10 × 4–5 mm at the apex, 11.5–14 × 4–6 mm at the base, those at the apex sessile, sometimes pedicellate, pedicels 1–4 mm long, yellowish-orange, sepals 1.5–3.5 × 1.5–2.5 mm, glabrous, triangular, no visible nerves, keeled, connate at the base, petals 8–10 × 2.5–4.0 mm at the apex, 9–19 × 3.5–4.5 mm at the base, with acute tips, slightly nerved; ovate-triangular, valvate, stamens 5–7 mm long; anthers 4–7 mm long, basally sagittate; filaments 2–3 mm long, free at the base, dorsifixed at the base (basifixed); pistillode trifid, ca 0.8–1.0 mm. Pistillate flowers elongate-pyramidal, 13–17 × 6–7 mm, orangish-yellow when immature and green when mature, glabrous; sepals 13–16 × 5–7 mm, orangish-yellow when immature and green when mature, without visible venation, triangular, imbricate; petals 10–13.5 × 3–5 mm, orangish-yellow when immature and green when mature, imbricate, triangular; pistil 6–8 × 3–4 mm, with whitish indumentum from the base of the pistil to nearly the base of the stigmas, stigmas 3–3 mm long, glabrous; inconspicuous staminodial ring rarely present, less than 0.5 mm in height, staminodes arranged in pairs or isolated (sometimes with anthers), six in number, ca 1.0–1.8 mm in height. Fruits ellipsoid, 2.1–3.0 × 1.6–2.0 cm, orange when mature, scaly lepidote tomentum, epicarp less than 0.5 mm thick, mesocarp less than 0.5 mm thick, succulent, and fibrous; endocarp 1.8–2.0 × 1.2–1.9 cm, 2–3 mm thick on the sides, 4–5 mm thick on the tips, trivittate interior. Seeds more or less ellipsoid, endosperm homogeneous. Germination remote tubular.

Distribution

The type population of Syagrus harenae was found in the village of Penha de França, in the Serra do Ambrósio mountain (Fig. 1A–E).

Habitat

The Serra do Ambrósio mountain is characterised by forest formations at its base, which end abruptly at an altitude of around 900 meters, giving way to open vegetation types, such as the carrascos (Meguro et al. 1994). The steepness of the slope, the thickness of the colluvial deposits and the texture of the sandy soils are the main factors determining the vegetation type found on these slopes (see Meguro et al. 1994; Pirani et al. 1994). In this transitional environment, the coarse white sand deposited by rainwater drainage derives from quartzite rocks (Meguro et al. 1994; CODEMIG 2012; Costa et al. 2016) and is the substrate of the area where the new species was discovered.

In areas with a gentle slope and sand deposition, at an altitude range of 800–1200 m, the vegetation is known as carrasco and is characterised by very ramified scrawny bushes, ranging from an open to dense physiognomy (Pirani et al. 1994; Oliveira et al. 2014). The new species is more abundant in the carrasco with dense physiognomy (Figs 3A, 7A–B, 8G, J–K). Costa et al. (2016) state that “sandy soils are common in the Espinhaço Range, but those in Serra do Ambrósio have a different granulometry”.

Figure 3. 

Vegetative morphological aspects of Syagrus harenae. A. Landscape photograph of the type locality: a group of individuals (white rectangles) growing on the sandy soils near rock outcrops (ro). B. The white arrowhead indicates the prostrated stem. C. Ramenta (black arrowheads) on the pinnae abaxial surface (ab) and leaf rachis with brownish tomentum (ra). D. Long tapering pinnae tips (white arrowheads). E. Pinnae: dark-green adaxial surface (ad) and glaucous abaxial surface (ab). F. Pinnae inserted in divergent planes over the rachis (rc). G. Fibres (white arrowheads) of the pseudopetiole. H. Leaf sheath (sh), peduncular bract (pb), and prophyll (pr). Photographs by Bruno F. Sant’Anna-Santos.

The climate of Serra do Ambrósio is Cwb according to the climatic classification of Köppen (1948), attenuated by altitude, with distinct wet and dry seasons, mean annual temperatures of 14.1–23.8°C and a mean annual rainfall of 1405 mm (Meguro et al. 1994). However, the air temperature at noon attains 30°C with air humidity at 40–50%, while 2 cm below the sandy soil surface the temperature can reach 40–50°C (Meguro et al. 1994). Where the vegetation is denser on the carrasco, the larger shrubs shade the herbaceous and low subshrubby species, and the sandy soil is partially or entirely covered by the leaf litter (Figs 3A–B, 8G, J–K). Besides retaining moisture, the leaf litter might reduce the soil temperature and release organic matter, favouring the greater number of S. harenae specimens observed in these places (Figs 3A–B, 7A–B, 8G–H, J–K).

The high floristic diversity in the carrasco includes species with large distribution (Pirani et al. 2014), such as Ananas ananassoides (Baker) L.B.Sm. (Fig. 7C), a common species throughout Brazil (Reflora 2024). Moreover, species characteristic of other mountains in the Espinhaço Range, such as Kielmeyera regalis Saddi. (Figs 3A, 7B) and Pilosocereus aurisetus (Werderm.) Byles & G.D.Rowley (Fig. 7D–E) are also common in the carrascos of Serra do Ambrósio. However, the flora in Serra do Ambrósio is also characterised by the presence of rare species (Pirani et al. 1994; Costa et al. 2018), such as Uebelmannia gummifera (Backeb. & Voll) Buining (Fig. 7F). The Serra do Ambrósio mountain should be highlighted as an outstanding conservation area for other botanical families, especially Eriocaulaceae (see Oliveira et al. 2014; Costa et al. 2016). To date, endemic species of Eriocaulaceae have been recognised for the Serra do Ambrósio (Pirani et al. 1994; Costa et al. 2016).

Ecology

After peduncular bract opening, the orangish-yellow flowers of S. harenae are prominent in the subshrub layer of the denser carrasco (Figs 7A, 8A–C, E). The staminate flowers remain orangish-yellow until they fall off (Figs 4A–H, M, 5A, 8A–C, E, G). On the other hand, the pistillate flowers transition from yellow to green over time (Figs 4A–H, M, 5A, 8A–C, E). Soon after the anthesis of the peduncular bract, the flowers are visited by flies (Fig. 8A), stingless bees (Fig. 8B–C), and beetles (Fig. 8D). In S. harenae, the beetles and their larvae intermingle among the flowers, covered in pollen grains (Fig. 8D–F).

Figure 4. 

Floral morphology of Syagrus harenae. A. Staminate flowers on rachillae upper 1/3 and triads on its lower 2/3: staminate flowers in pre-anthesis (two black arrowheads). B. Tetrads (two white circles): staminate flowers in anthesis (two black arrowheads). C. Inflorescence bearing only pistillate flowers (after staminate flowers’ senescence). D. Triad: sessile staminate flowers, yellow pistillate flowers. E. Pedicellate staminate flowers (two black arrowheads), green pistillate flowers. F. Tetrad: two central pistillate flowers flanked by two staminate flowers. G. Pentad on lateral view: three central pistillate flowers flanked by two staminate flowers (two black arrowheads). H. Pentad: top view. Staminate flowers (two black arrowheads). I. Apex and base staminate flowers. Three petals (pe). J. Staminate flower: petals (pe) longer than the sepals (se). K. Keeled sepals (white arrowhead). Petals (pe) slightly veined (black arrowhead). L. Valvate petals (pe). M. Six stamens (six white dots). NO. The anther is dorsifixed at the filament base (fi). Anther (an) basally sagittate. Conective (white arrowhead). P. Stamen: anther (an) and filament (fi). Q. Longitudinal dehiscence (white arrowhead) and pistillode (white circle). R. Trifid pistillode (pi). Photographs by Bruno F. Sant’Anna-Santos.

Figure 5. 

Floral morphology of Syagrus harenae. A. Floral bracteole (black arrowhead). B. Perianths removed from four different pistillate flowers, bearing two sepals (se) and four petals (pe) or three sepals and four petals. C. Imbricate outer (ou) and inner sepals (in). D. Sepal (se): smooth margin (black arrowhead). EF. Imbricate petal tips. G. Outer (ou) and inner (in) petals. HI. Pistillate flower: ovary (ov), stigma (st) and staminodes with anther (an) and without (black arrowheads). J. Whitish indumentum (id). Staminode (st). Photographs by Bruno F. Sant’Anna-Santos.

Figure 6. 

Fruit morphology of Syagrus harenae. A. Infructescence. B. Immature fruit: epicarp green in colour and recovered by a scaly lepidote tomentum. C. Mature fruit: epicarp orange in colour and recovered by a scaly lepidote tomentum. D. Fibrous mesocarp (me). Epicarp (ep). Endocarp (en). E. Three apical endocarp pores: top view. F. Endocarp pore, lateral view. G. Longitudinal section: brownish endocarp (en) and whitish endosperm (ed). Photographs by Bruno F. Sant’Anna-Santos.

Figure 7. 

Habitat of Syagrus harenae. A. Landscape view of the carrasco: the small Syagrus harenae (sy), sandy soil (sa), and forest (fo). B. Open (op) and dense (de) carrasco vegetation. S. harenae (sy), forest (fo), and Kielmeyera regalis (ky). C. Ananas ananassoides. D. Rocks (ro). Pilosocereus aurisetus (pi). E. Fruits (fr) of Pilosocereus aurisetus (pi). F. Uebelmannia gummifera. Photographs by Bruno F. Sant’Anna-Santos.

Figure 8. 

Morphological aspects of Syagrus harenae with ecological implications. A. Fly on the peduncular bract. B. A bee visiting a pistillate flower. C. A bee visiting a staminate flower. D. Beetle. EF. Larvae (two white arrowheads). GH. Fruits and endocarps on the sandy soil. I. Mesocarp damaged (da) by fruit predation. JK. Pendulous infructescences almost reaching the ground (three white circles), and young plants (two white arrowheads) near adult plants. Photographs by Bruno F. Sant’Anna-Santos.

Palms are well-known as hotspots for insect abundance and diversity, but so far for Syagrus, the evidence points to pollination both by beetles and bees (Silberbauer-Gottsberger et al. 2013; Núñez-Avellaneda et al. 2015; Guerrero-Olaya and Núñez-Avellaneda 2017; Núñez-Avellaneda and Carreño 2017). According to Medeiros et al. (2019), beetles breed on floral tissues of S. coronata as larvae. Besides pollen, nectar is another floral reward associated with Syagrus (Silberbauer-Gottsberger et al. 2013). In addition, the presence of osmophores in pistillate flowers has already been recorded for the genus (see Sant’Anna-Santos et al. 2023a). In S. harenae, nectar drops were not observed, a strong sweet odour was released, and the visit of bees to both pistillate and staminate flowers may indicate that they are looking for a resource other than just pollen (Fig. 8B–C). However, future studies will be necessary to identify which secretory structure is associated with offering rewards to pollinators and verify the presence of osmophores or nectaries in S. harenae.

In Syagrus, most species display flowers in shades ranging from green to yellow (see Noblick 2017a), but the re-greening of flowers after anthesis is rare. This phenomenon has only been documented twice: first in Syagrus coronata (Mart.) Becc. (Medeiros et al. 2019) and now in Syagrus harenae. Flower colour changes after anthesis (e.g. Weiss 1995; Lunau 1996; Nadot and Carrive 2021) due to ageing or pollination, though observed across various plant taxa, are relatively uncommon (Ruxton and Schaefer 2016) and are often seen as signals to pollinators (Weiss 1995). Notwithstanding, Ruxton and Schaefer (2016) argue that there is limited evidence that floral colour change is sufficiently beneficial in modifying pollinator behaviour to evolve and be maintained.

Re-greening after anthesis, while rare in flowers, has been reported in some species (see Weiss 1995; Knapp et al. 2001; Medeiros et al. 2019; Sun et al. 2021). It is more common in extrafloral organs, where it may provide energy for seed development (Pélabon et al. 2015) and, in a Zantedeschia hybrid, was due to the masking of carotenoids by chlorophyll (Chen et al. 2009). In S. harenae and S. coronata, the re-greening occurs in entire pistillate flowers, which may point to a dual strategy: signalling pollinators while contributing to energy production. The occurrence of dimorphism in floral colours (sexual dichromatism) in two species of Syagrus warrants further studies to investigate its role in the group’s evolution.

On the soil, next to the specimens of S. harenae, it is noticeable that many fruits from different reproductive periods are deposited just below the infructescences where they were produced (Fig. 8G–I). As they ripen, the fruits increase in weight, and the infructescence draws closer to the ground (Fig. 8J–K), where the fruits complete their ripening and fall. The large number of fruits close to the mother plant, with the mesocarp only partially consumed (Fig. 8G–I), provides evidence that animals feeding on these fruits are either not able to swallow or are not able to carry their seeds. In addition, it was very common to observe young plants next to the mother plant (Fig. 8J–K).

For rare species such as S. harenae, natural selection would probably favour limited dispersal where drivers such as environmental conditions, surrounding vegetation and ineffective dispersal would be relevant causes of philomatry (Cheplick 2022). According to this author, the mother-site hypothesis (MSH) proposes that the selection should favour philomatry in a population adapted to a particular habitat because offspring will likewise be adapted to that same habitat. Philomatry can be applied to a plant species with limited spatial dispersal and a tendency for their offspring to remain in the site where they were produced (Cheplick 2022). Therefore, MSH can at least partly explain the several rare species of Syagrus along the Espinhaço Range and should be further explored to understand the ecology and evolution of these species.

Phenology

The new species was collected with flowers and fruits in February 2024.

Etymology

The specific epithet, harenae, means sand and refers to the unique sandy soil where the new species grows in the Serra do Ambrósio mountain.

Preliminary IUCN conservation assessment

The population of the new species has only been recorded in the Serra do Ambrósio mountain, where there is no conservation unit. Close to the type population, there is a mining site for sand extraction, which has been closed. Sand extraction has also been recorded in other parts of Serra do Ambrósio (see Costa et al. 2018: fig 4a). Taking into account the area of occupancy (AOO = 12 km2) and the extent of occurrence (EOO = 1.231 km2), and according to the IUCN (2022) categories and criteria, S. harenae should be considered Critically Endangered (CR): B1ab(i,iii).

Additional specimens examined.

BRAZIL – Minas Gerais • Rio Vermelho, Pedra Menina, Serra do Ambrósio, Morro da Virada do Mato Virgem; 31 Jul. 1985; fl.; Mello-Silva et al. 7833; SPF • Penha da França, ca 100 km ao nordeste de Diamantina; 18°4’48”S, 43°4’48”O; 11 Mar. 1995; Splett 875; UB.

Pinnae anatomy

Stomata occur only on the abaxial surface (Fig. 9A–B), with guard cells located at the same level as ordinary epidermal cells (Fig. 9B). In the transverse section of the pinnae, the subsidiary cells are arciform and located entirely beneath the cuticle level (Fig. 9B). The hypodermis on both surfaces of the pinnae consists of one to two layers of cells that are elongated longitudinally or have a quadrangular shape (Fig. 9A–B). The hypodermis forms two layers between the adaxial non-vascular fibre bundles (Fig. 9A). On the abaxial surface, the hypodermis is interrupted by substomatal chambers (Fig. 9B). Tiny fibres and rounded groups with a larger number of fibres are observed in the abaxial hypodermis (Fig. 9C–E). Large fibre bundles are connected to the adaxial hypodermis and reach nearly ½ across the mesophyll (Fig. 9E). The primary vascular bundles are connected to the adaxial hypodermis and are always entirely surrounded by fibres (Fig. 9E, H). The primary vascular bundles always have a larger diameter, two phloem poles, and noticeable protoxylem and metaxylem elements (Fig. 9E). The secondary and tertiary vascular bundles are only abaxially surrounded by a sclerenchymatous sheath (Fig. 9C, E–G, I). While the secondary vascular bundles are non-connected to the abaxial hypodermis, the tertiary vascular bundles are connected to the abaxial hypodermis (Fig. 9C, E–G, I). The mesophyll is dorsiventral, with four to six bands of palisade parenchyma near the hypodermis on the adaxial surface and 10 to 12 chlorenchyma layers adjacent to the abaxial surface (Fig. 9I). Regarding the margin, there is a large first adaxial non-vascular fibre bundles and, sometimes, a tertiary vascular bundle connected to the adaxial hypodermis (Fig. 9I). The midrib is transversally triangular and adaxially projected, and the expansion tissue is interrupted and packed with fibre groups (Fig. 9J–K). The main vascular system of the midrib consists of five collateral bundles, surrounded by a fibrous ring and 1 accessory bundle with a reinforced sheath connected to the adaxial hypodermis (Fig. 9J, N). There are 2–4 non-vascular fibre bundles around the fibrous ring (Fig. 9M). Table 2 compares the pinnae anatomy of S. harenae, S. aristeae, S. duartei, S. evansiana, and S. glaucescens.

Figure 9. 

Pinna anatomy of Syagrus harenae using LM with cross-sections. A. Bisseriate hypodermis (hy) between the adaxial non-vascular fibre bundles (fi). Adaxial epidermis (ad), cuticle (cu). B. Arciform subsidiary cells (two red dots) and guard cells (two black dots) are at the same level as the abaxial epidermis (ab). Cuticle (cu), hypodermis (hy), substomatal chamber (sc). CD. Minor fibres (three white circles) and rounded groups with many fibres (three black circles). E. Primary (t1) vascular bundles connected to the adaxial hypodermis, secondary (t2) vascular bundles unconnected, and tertiary (t3) vascular bundles connected only to the abaxial hypodermis. F. Secondary (t2) vascular bundle abaxially surrounded by a sclerenchymatous sheath (ss). G. Tertiary (t3) vascular bundle abaxially surrounded by a sclerenchymatous sheath (ss). H. Primary vascular bundle: protoxylem (pr), metaxylem (me), two poles of phloem (ph) and sclerenchymatous sheath (ss) connected to hypodermis on both surfaces. I. Pinnae margin: large first (lf) adaxial non-vascular fibre bundles and adaxial tertiary vascular (t3) bundle. J. Midrib: fibrous (fr) ring reaching the abaxial hypodermis (black arrowhead) and interrupted expansion tissue (et). K. Detail of the expansion tissue: fibres (fi). L. Collateral fibre bundles (five black circles) and phloem poles (ph). M. Non-vascular (nv) fibre bundle. N. Accessory bundle (ab). Photographs by Bruno F. Sant’Anna-Santos.

Figure 10. 

Morphological differences between Syagrus harenae (A, C, E, G, I) and Syagrus glaucescens (B, D, F, H, J). A. Prostrated stem (pr), lax (la) pinnae, and symmetrical (sy) pinnae tip. B. Erect stem (er), congested (co) pinnae, and asymmetrical (as) pinnae tip. C. Lax sheathing leaf base. D. Congested sheathing leaf base. E. Inconspicuous leaf scars on the stem base (st). F. Conspicuous leaf scars on the stem base (st). G. Strongly pendulous inflorescence. H. Erect inflorescence. I. Peduncle of the inflorescence with scattered thin indumentum. J. Peduncle of the inflorescence glabrous. Photographs by Bruno F. Sant’Anna-Santos.

Notes

All the known species in the Syagrus glaucescens complex occur in neighbouring regions of the Espinhaço Range in the state of Minas Gerais (Fig. 1A): Serra do Cipó, Diamantina Plateau, Serra do Cabral massif, and northern mountains complex (Noblick 2017a; Firmo et al. 2021; Sant’Anna-Santos et al. 2023c). Syagrus glaucescens Glaz. ex. Becc. is one of the rupicolous species found mainly on the Diamantina Plateau (see Fig. 1A). To the south of the Diamantina Plateau, in the region known as Serra do Cipó, Syagrus duartei Glassman was the second species described for the complex (see Glassman 1968), and perhaps the most controversial. Also rupicolous, in the Flora Palmae da Serra do Cipó by Marcato and Pirani (2001), the authors did not recognise a morphological basis to support S. duartei as a species distinct from S. glaucescens. In fact, S. duartei is similar to S. glaucescens, and they are likely related and probably sympatric in the northernmost portion of the Serra do Cipó (Noblick 2017a; SpeciesLink Network 2024). However, Marcato and Pirani (2001) did not consider anatomical data from Glassman (1972), which supported the species as distinct taxa – which was later corroborated by Noblick (2010, 2017a).

The third species in the complex, the dwarf Syagrus evansiana Noblick, is more easily differentiated from S. duartei and S. glaucescens by characteristics such as acaulescence, leaves not arranged in vertical rows, spiciform inflorescences (not just branched) and the rare variation of 3 to 5 pores in the endocarp (Noblick 2009; 2010; 2017a; Sant’Anna-Santos et al. 2023c). Populations of S. evansiana have been recorded along the Espinhaço Range, such as in the disjunct Serra do Cabral and Serra do Ambrósio (see Noblick et al. 2014; Noblick 2017a; Firmo et al. 2021; SpeciesLink Network 2024). In Serra do Cabral, morphological and anatomical studies showed that although similar to S. evansiana, the population was a fourth distinct species for the complex – the also dwarf and rupicolous Syagrus aristeae Sant’Anna-Santos (Firmo et al. 2021; Sant’Anna-Santos et al. 2023c). The discovery of S. aristeae raised the suspicion that other populations thought to be S. evansiana, but without a greater collection effort and detailed morphoanatomical studies, could be unresolved species. Especially in the case of disjunct mountains with records of rare and microendemic species – such as the Serra do Ambrósio (see Costa et al. 2016).

The first record in the Serra do Ambrósio dates back to 1985, viz. Mello-Silva et al. 7833 (Pirani et al. 1994; SpeciesLink Network 2024). Although identified as S. glaucescens, the specimen has a very short stem, a characteristic of S. evansiana. A decade later, a second S. glaucescens was recorded in the Serra do Ambrósio. However, 20 years after the collection, the identity of Splett 875 was changed to S. evansiana and the Serra do Ambrósio was then included as an area of occurrence for both species (see Noblick 2017a; SpeciesLink Network 2024).

Identification key for the Syagrus glaucescens species complex

1 Plants with aerial above-ground stems; leaf bases in rows, inflorescences always branched; endocarp 1.8–3.5 mm long, only three endocarp pores, 2–8 mm thick on the sides 2
Plants with very short or subterranean stems (acaulescents); leaf bases not in rows on the stem, unbranched to branched inflorescences; endocarp 1.4–1.8 mm long, three to five endocarp pores, 1 mm thick on the sides 3
2 Stem base round in appearance, with inconspicuous leaf scars; lax pinnae on the leaf rachis; abaxial side of the petiole and leaf rachis with tomentum; peduncle with scattered indumentum; inflorescences strongly pendulous, pistillate flowers with imbricate petal tips; number of sepals 2–4; number of petals 3–4; inconspicuous staminodial ring Syagrus harenae
Stem base angular in appearance, with conspicuous leaf scars; congested pinnae on the leaf rachis; abaxial side of the petiole and leaf rachis glabrous; peduncle glabrous; inflorescences slightly pendulous or erect; pistillate flowers with valvate petal tips; number of sepals 3; number of petals 3; conspicuous staminodial ring 4
3 Leaf rachis 94–145 cm long; middle pinnae tip usually asymmetrical; abaxial side of leaf rachis and petiole with tomentum; inflorescence axis 18–29.5 cm long; basal and apical rachillae of similar length; epicarp covered with crackled plates Syagrus aristeae
Leaf rachis 21–92 cm long; middle pinnae tip usually symmetrical; abaxial side of leaf rachis and petiole glabrous; inflorescence axis 4.5–17 cm long; basal and apical rachillae of different length; epicarp covered by a thick brown indumentum Syagrus evansiana
4 Stem usually erect; pistillate flowers 10–17 mm long; fruit ellipsoid, 2–3 cm long; endocarp ellipsoid to ovoid, 2–2.8 cm long, 2–4 mm thick on its sides Syagrus glaucescens
Stem usually prostrate (occasionally erect); pistillate flowers 17–25 mm long; fruit globose, 2.8–3.5 cm long; endocarp nearly globose, 2.8–3.5 cm long, 5–8 mm thick on its sides Syagrus duartei

Conclusion

Our results show that, despite its short stem, the population from Serra do Ambrósio is not acaulescent like S. evansiana, and more closely resembles S. glaucescens due to the vertically arranged leaves. However, we were confident it was a new and undescribed species on our first encounter with the plant. Of course, although the Serra do Ambrósio is a disjunct area, S. harenae is geographically closer to S. glaucescens, reinforcing their relationship. However, the presence of flowers in tetrads in practically all the specimens evaluated and the first record of flowers in pentads for Syagrus also pointed to a striking species. Other characters, such as the re-greening of pistillate flowers, the imbricate petal tips in pistillate flowers, the variation in the number of sepals, and the basifixed anthers, also make S. harenae an impressive species that sets it apart from all other species of Syagrus in the region. According to Rabinowitz (1981), the uniqueness of the environment is a determining factor to indicate the rarity of a species, and the carrascos where S. harenae is found are unique. As far as we know, only Syagrus cabraliensis (Noblick & Lorenzi) Sant’Anna-Santos has a habitat as unique as S. harenae: the ferruginous cangas of the Serra do Cabral (Noblick et al. 2014; Sant’Anna-Santos et al. 2023a). Therefore, due to the differences pointed out here, it is clear that the Serra do Ambrósio population is a distinct species and the fifth to make up the Syagrus glaucescens complex.

Our results here confirm what Noblick and Lorenzi (2010) established, that the knowledge of the plant in its natural habitat and the leaf anatomy are essential for a better delimitation of these puzzling palm species. Furthermore, our results, together with data from recent studies (Firmo et al. 2021; Noblick and Sant’Anna-Santos 2021; Sant’Anna-Santos 2021, 2023; Sant’Anna-Santos et al. 2023a, 2023b, 2023c; Carvalho et al. 2024) indicate that we need to assess each population individually, as the diversity of Arecaceae in highland environments is still underestimated. Many of these hitherto unresolved species are outside the boundaries of protected areas, so there is an urgent need to re-evaluate these populations due to the accelerated destruction of their habitat. Unlike many morphological characters lost in the herborisation process, the anatomy is preserved. Thus, it is a valuable tool for deciding which populations should be prioritised for studies – in conjunction with analysing satellite images, which easily demonstrate areas threatened by anthropisation (see Sant’Anna-Santos et al. 2023a). Therefore, searching for discoveries favouring biodiversity conservation in Arecaceae may lie precisely within herbarium collections, and anatomy can be an essential tool and starting point for this work.

Acknowledgements

We thank Dr Patrícia Soffiatti for the valuable suggestions and the anonymous reviewers for the valuable comments and correction made to the manuscript.

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