118 urn:lsid:arphahub.com:pub:71cc5dc6-a767-5334-951f-ef6ae8936459 Plant Ecology and Evolution plecevo 2032-3913 2032-3921 Meise Botanic Garden and Royal Botanical Society of Belgium 10.5091/plecevo.185113 185113 Research Article Angiospermae Poaceae Biodiversity & Conservation Morphology & Anatomy Systematics Africa Madagascar Phylogenetic and morphological data support a new combination for a grass endemic to Madagascar and nearby islands: Trichanthecium ambositrense (Poaceae) Lopes-Neto Ray Balieiro rblopesneto@gmail.com https://orcid.org/0000-0003-4179-2713 1 Conceptualization Writing - original draft Writing - review and editing Data curation Funding acquisition Methodology Visualization Patrícia Pantoja Serrão Filgueira Joana https://orcid.org/0000-0002-9732-6052 2 Writing - review and editing Data curation Methodology Visualization Hackel Jan https://orcid.org/0000-0002-9657-5372 3 Writing - review and editing Data curation Methodology Vorontsova Maria S. https://orcid.org/0000-0003-0899-1120 4 Writing - review and editing Data curation Methodology Lage Viana Pedro https://orcid.org/0000-0001-5044-0758 5 Conceptualization Writing - original draft Writing - review and editing Data curation Funding acquisition Methodology Omar Zuloaga Fernando https://orcid.org/0000-0003-2794-539X 6 Conceptualization Writing - original draft Writing - review and editing Data curation Methodology Museu Paraense Emílio Goeldi, Belém, Pará, Brazil Royal Botanic Gardens Kew United Kingdom https://ror.org/00ynnr806 Instituto Tecnológico Vale, Belém, Pará, Brazil Museu Paraense Emílio Goeldi Belém Brazil https://ror.org/010gvqg61 Department of Ecology, Environment and Plant Sciences, Stockholm University, Stockholm, Sweden Instituto Nacional da Mata Atlântica Santa Teresa Brazil https://ror.org/0395f2d85 Royal Botanic Gardens, Kew, Richmond, UK Instituto de Botánica Darwinion San Isidro Argentina https://ror.org/0594de127 Instituto Nacional da Mata Atlântica, Santa Teresa, Espírito Santo, Brazil Department of Ecology, Environment and Plant Sciences, Stockholm University Stockholm Sweden https://ror.org/05f0yaq80 Instituto de Botánica Darwinion, San Isidro, Buenos Aires, Argentina Instituto Tecnológico Vale Belém Brazil https://ror.org/05wnasr61

Corresponding author: Ray Balieiro Lopes-Neto (rblopesneto@gmail.com)

Academic editor: Isabel Larridon

 2026 02 07 2026 159 2 415 430 B5B9BED9-A8B7-55F8-A12C-3153A8BC0F14 14 01 2026 07 05 2026 Ray Balieiro Lopes-Neto, Joana Patrícia Pantoja Serrão Filgueira, Jan Hackel, Maria S. Vorontsova, Pedro Lage Viana, Fernando Omar Zuloaga This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

Backgrounds and aims – Trichanthecium is a grass genus composed of species transferred from Panicum and is positioned in an incertae sedis clade in the tribe Paniceae (“Sacciolepis grex” clade), formed exclusively by C3 taxa. Currently, the genus possesses 52 species occurring in tropical and subtropical America, Africa, and Madagascar. Trichanthecium perrieri is the only species endemic to Madagascar and is morphologically related to another endemic species: Panicum ambositrense. We evaluated the position of P. ambositrense in the “Sacciolepis grex” clade, and applied an integrative approach, combining phylogenetic, anatomical, and morphological analyses to assess whether the species belongs to Trichanthecium.

Material and methods – The phylogenetic analyses were conducted using previously published plastid markers (ndhF and rbcL). Anatomical analysis was used to describe the cross-sectional and epidermal leaf anatomy, and the taxonomic treatment was based on herbarium material, focusing on the macromorphological description of the species, micromorphological description of the upper anthecium (with scanning electron microscopy), and taxonomic comparative comments to other species.

Key results – The phylogenetic analyses confirmed the position of P. ambositrense within the Trichanthecium clade, in a group with T. aequinerve and T. perrieri. Anatomical analysis indicated that the species has C3 photosynthesis, based on the presence of two sheaths without specialized chloroplasts surrounding the vascular bundles and six to ten mesophylls cells with specialized chloroplasts between consecutive vascular bundles. The taxonomic analysis indicated that P. ambositrense matches the morphological concept of Trichanthecium.

Conclusion – A new combination, Trichanthecium ambositrense, is presented along with its morphological description, a distribution map, an illustration, data on its distribution, habitat and phenology, a preliminary conservation status assessment (Vulnerable), and taxonomic comments on related species. The species of Trichanthecium occurring in Madagascar are listed and discussed, and an updated identification key is presented for the Old World species of the genus.

 Comoros endemism foliar anatomy Gramineae Old World Madagascar Paniceae Panicum “Sacciolepis grex” clade taxonomy Introduction

Panicum L., as traditionally circumscribed, is one of the richest genera of the tribe Paniceae (Poaceae, Panicoideae), with ca 600 species distributed worldwide (Clayton and Renvoize 1986; Zuloaga 1987). The morphology of the spikelets is mostly uniform, but other morphological, anatomical, and physiological characters are variable in the genus (Clayton and Renvoize 1986; Webster 1988; Zuloaga 1987; Crins 1991). In the 20th century, many infrageneric classifications have been proposed, including in studies focused on the Flora of Tropical Africa (Stapf 1920) and North America (Hitchcock and Chase 1910, 1915), and subsequent overall proposals for subgenera and sections, utilizing morphological, anatomical, and karyological characters (Pilger 1931, 1940; Hsu 1965; Brown 1977; Zuloaga 1987).

Later, morphological and molecular studies indicated that the genus is polyphyletic (Gómez-Martínez and Culham 2000; Zuloaga et al. 2000; Duvall et al. 2001), with representative species in the tribes Paniceae and Paspaleae. Aliscioni et al. (2003), in a comprehensive study of the genus, limited Panicum (sensu stricto) to Panicum subg. Panicum, with 163 species distributed worldwide, all with C4 photosynthesis, and the other species of Panicum (sensu lato) were positioned as incertae sedis in Paniceae and Paspaleae. Recently, several studies focused on Panicum s.l. resulted in the transfer of taxa to other genera and the proposal of new genera to accommodate these species (Aliscioni et al. 2003; Simon and Jacobs 2003; Bess et al. 2006; Morrone et al. 2007, 2008, 2012; Zuloaga et al. 2007, 2010, 2011, 2015, 2020, 2024; Sede et al. 2008, 2009; Delfini et al. 2023a; Scataglini and Zuloaga 2013; Grande Allende 2014; Scataglini et al. 2014a, 2014b; Nicola et al. 2015; Silva et al. 2025).

Among the new genera is Trichanthecium Zuloaga & Morrone, which was originally circumscribed with 38 species formerly included in Panicum sect. Parvifolia Hitchc. & Chase ex Pilg. and Panicum sect. Verruculosa Stapf (Zuloaga et al. 2011); this genus is positioned in the tribe Paniceae, in an incertae sedis group named the “Sacciolepis grex” clade, composed of Trichanthecium, Kellochloa Lizarazu, Nicola & Scataglini, Sacciolepis Nash, and some species of Panicum s.l., all with C3 photosynthesis (Soreng et al. 2022; Zuloaga et al. 2024). Since the genus was proposed, one new species from the Republic of Guinea (Xanthos et al. 2020) and another from the Democratic Republic of the Congo, together with 12 new combinations of African Panicum s.l. species, have been published (Zuloaga et al. 2024).

Currently, the genus comprises 52 species distributed in tropical and subtropical areas of America, Africa, and Madagascar (Zuloaga et al. 2024). The genus consists of annual and perennial herbs, with decumbent or erect culms, bearing axillary or terminal panicles with solitary spikelets on long pedicels, the lower glume being (1/6–)1/2–1 times as long as the spikelet, nerveless to 1–3(–5)-nerved, upper glume and lower lemma 3–5(–7)-nerved and upper anthecium smooth, ornamented with simple papillae and bicellular microtrichomes or rarely glabrous, and sometimes unicellular macrotrichomes present at the apex (Zuloaga et al. 2011, 2024).

Trichanthecium perrieri (A.Camus) Zuloaga is the only species of the genus endemic to Madagascar, and was originally described by Camus (1925) in Panicum. In this study, Camus (1925) also described Panicum ambositrense A.Camus, a species morphologically similar to P. perrieri A.Camus (= T. perrieri), mainly by the prostrate culms, rooting at the lower nodes, leaves regularly distributed along the culms, with linear or linear-lanceolate blades, terminal synflorescence, and narrowly ovoid spikelets. Both species are found in high elevation regions of central and northern Madagascar, often in wet and humid areas of forest understory (Vorontsova 2018). Hackel et al. (2018) sequenced P. ambositrense and placed it in a clade with P. perrieri and P. aequinerve Nees, these taxa forming a sister clade to Trichanthecium, in the “Sacciolepis grex” clade. Zuloaga et al. (2018) did not include P. ambositrense in their analysis, but indicated P. perrieri and P. aequinerve to be part of a group with P. acrotrichum Hook.f., P. calvum Stapf, P. chionachne Mez, P. eickii Mez, and P. inaequilatum Stapf & C.E.Hubb., all of them forming a clade embedded in Trichanthecium. All these species were combined in Trichanthecium by Zuloaga et al. (2024), but P. ambositrense has not been evaluated yet.

Following the recent studies focused on Trichanthecium (Zuloaga et al. 2024; Lopes-Neto et al. 2025), the aim of this paper is to analyse whether P. ambositrense belongs in the Trichanthecium clade, and if the anatomical and morphological characteristics of the species are in accordance with the delimitation for the genus. To reach this goal, we performed a phylogenetic analysis, based on previously published plastid markers (ndhF and rbcL), a cross-sectional leaf anatomy analysis, which was produced to characterize the organization of the vascular bundles and infer the photosynthetic pathway, and a taxonomic analysis based on herbarium material is also presented and discussed, including a macromorphological description of the species, micromorphological analysis of the upper anthecium, and taxonomic comparative comments.

 Material and methods Anatomical and micromorphological analysis

The foliar anatomy analysis was produced by extracting the second blade below the synflorescences of the following herbaria materials: M. Vorontsova et al. 736 (K), N.H. Rakotomalala et al. 552 (K), and O.P. Nanjarisoa et al. 138 (K). The leaves were subjected to the herbarium reversal process (Smith and Smith 1942) and stored in 70% ethanol, dehydrated through an ethanol series, and embedded in methacrylate resin (Historesin, Leica®). Transverse sections (5 µm) were obtained with a rotary microtome (Leica RM 2245) and stained with toluidine blue at pH 4.0 (O’Brien et al. 1964). For the analysis of the epidermal surface, the epidermal fingerprint technique followed Segatto et al. (2004). Epidermal impressions were used to describe the general distribution and organization of epidermal structures. However, to obtain clearer and more detailed records of the observed features, paradermal hand-cut sections were prepared from both adaxial and abaxial surface using a razor blade and stained with toluidine blue, pH 4.0 (O’Brien and McCully 1981). All sections were examined and photographed under an optical microscope (DM750, Leica®) equipped with a digital camera (Leica CH-9134). Anatomical analyses and morphological terminology followed Ellis (1976, 1979).

The scanning electron microscopy (SEM) images of the upper anthecium were conducted in the Laboratório Institucional de Microscopia Eletrônica de Varredura of Museu Paraense Emílio Goeldi (Belém do Pará, Brazil), using a TESCAN electron microscope (model Mira3, with a FEG type electron gun). The upper anthecia were extracted from the lectotype J.M.H.A. Perrier de la Bâthie 10851 (P00450276), and they were mounted on metal stubs and sputter coated with gold, depositing a layer of 10–15 nm. The secondary electron detection images were generated using a voltage acceleration of 5 kV and a working distance of 15–20 nm. The micromorphological description was produced based on adapted terminology of Ellis (1979) and Zuloaga et al. (2011, 2024). The anatomical and SEM images were assembled using Adobe Photoshop 2024.

 Phylogenetic analysis

To confirm the position of Panicum ambositrense within the Trichanthecium clade, we added the species’ two plastid sequences (ndhF and rbcL) previously published by Hackel et al. (2018) in a combined dataset with representative species of the “Sacciolepis grex” clade of the tribe Paniceae (sensu Soreng et al. 2022), which includes the genera Kellochloa, Sacciolepis, Trichanthecium, and 19 species of Panicum s.l. (including P. ambositrense). The ingroup represents the “Sacciolepis grex” clade, and the outgroup is composed of species of tribes Thysanolaeneae, Andropogoneae, Paspaleae, and other Paniceae taxa (including Panicum s.str.). The complete dataset was combined with sequences obtained from GenBank and includes 115 accessions and 102 species. The list of vouchers, species, and GenBank accessions is available as supplementary material (Suppl. material 1).

Datasets of the individual markers were aligned using ClustalW (Larkin et al. 2007), in MEGA v.11.0.3 (Tamura et al. 2013), then concatenated using Mesquite v.3.81 (Maddison and Maddison 2023). Maximum Likelihood (ML) and Bayesian Inference (BI) analyses were performed using RAxML v.8.2.12 (Stamatakis 2014) and MrBayes v.3.2.7a (Ronquist and Huelsenbeck 2003), on the CIPRES platform (Miller et al. 2010). The ML analysis used 1000 rapid bootstraps inferences and a thorough ML analysis under the GTR+G model. The BI analysis used a Markov chain Monte Carlo (MCMC) run for 10,000,000 generations, sampling every 1000 generations, applying the GTR+G model. Convergence and effective sample size (ESS > 200) were checked using Tracer v.1.7.2 (Rambaut et al. 2018). The majority-rule consensus tree of the BI analysis was produced after discarding the first 25% trees as burn-in; the resulting tree was edited in FigTree v.1.4.4 (http://tree.bio.ed.ac.uk/software/figtree) and InkScape (https://inkscape.org).

 Taxonomic treatment

The taxonomic treatment was produced based on material deposited in the following herbaria: BR, G, K, MO, P, S, TAN, and US (acronyms follow Thiers 2026). The morphological description was prepared using terminology adapted from Zuloaga et al. (2011, 2024); the indumentum terminology is based on Harris and Harris (2001). Distribution area, habitat and phenology data were extracted from information available on the exsiccatae labels. Morphological comparison between related species in Trichanthecium and the ones registered in Madagascar and nearby islands were prepared using taxonomic revisions (Zuloaga et al. 2011, 2024; Vorontsova 2018) and analysis of herbarium material (list of exsiccatae available in Suppl. material 2).

The conservation status assessment was produced based on the IUCN Red List Categories and Criteria (IUCN Standards and Petitions Committee 2024). To calculate the area of occupancy (AOO) and extent of occurrence (EOO), we used the Geospatial Conservation Assessment Tool (GeoCAT) (Bachman et al. 2011), applying 2 × 2 km grid cells.

The distribution map was prepared using QGIS v.3.8 (QGIS Development Team 2019); the cartographic base comprises Google satellite images and shapefiles provided by GeoBoundaries (https://www.geoboundaries.org). The coordinates of the specimens were extracted from the sheet labels, and the materials without precise coordinates were included using approximate coordinates based on the locality information on the exsiccatae (list of exsiccatae and coordinates available in Suppl. material 3).

 Results Anatomical and micromorphological analysis <italic>Leaf anatomy description</italic> <italic>Adaxial epidermis</italic>

The costal zone consists of vertically elongated long cells with sinuous anticlinal walls, alternating with silica cells that are vertically arranged and exhibit dumbbell- to saddle-shaped outlines (Fig. 1A). In the intercostal zone, bulliform cells are hexagonal to rectangular in outline, less vertically elongated, and display sinuous to undulated anticlinal walls. Prickles are present (Fig. 1B), whereas stomata are rarely observed in this region.

10.5091/plecevo.185113.figure1 9F776B65-E028-5EFE-A964-2DE75D3FC5F5

Leaf anatomy and micromorphology of the upper anthecium of Trichanthecium ambositrense. A–C. Epidermis in surface view (N.H. Rakotomalala et al. 552, K). A–B. Adaxial surface. C. Abaxial surface. D–G. Transverse sections of the leaf (O.P. Nanjarisoa et al. 138, K). D. Midrib region. E. Mesophyll. F. Inner margin. G. Outer margin. H–M. SEM of the upper anthecium (J.M.H.A. Perrier de la Bâthie 10851, P). H–J. Upper anthecium, dorsal view. K–M. Upper anthecium, ventral view. Abbreviations: bc – bulliform cell; sc – silica cell; st – stoma; pk – prickle; mi – bicellular microtrichome. Scale bars: A–G = 20 µm; I–J, L–M = 200 µm; H, K = 500 µm.

https://binary.pensoft.net/fig/1704802 <italic>Abaxial epidermis</italic>

The abaxial surface exhibits long cells arranged in a pattern similar to that of the adaxial surface. Stomata are arranged in two parallel rows, each positioned along opposite margins of the intercostal zones, with stomatal apparatuses surrounded by dome-shaped subsidiary cells (Fig. 1C). Macrotrichomes and bicellular microtrichomes are present within the intercostal zones (Fig. 1C).

 <italic>Cross-section</italic>

The leaf blade presents a uniseriate epidermis, with adaxial epidermal cells and bulliform cells arranged in groups of three to five cells (Fig. 1D–E). The mesophyll consists of two to three compact cell layers, the first adaxial layer being vertically elongated (Fig. 1E–F). Collateral vascular bundles of first- and second-order are present, each surrounded by two sheaths without specialized chloroplasts (Fig. 1D–E). The midrib is abaxially projected, with a complex simple system composed of a first-order vascular bundle oriented abaxially and surrounded by two sheaths lacking specialized chloroplasts, in addition to a thick sclerenchyma cluster (Fig. 1D).

 <italic>Margins</italic>

Structurally dimorphic; the inner margin is obtuse (Fig. 1F), and the outer margin is acute (Fig. 1G).

 <italic>Upper anthecium micromorphology</italic>

Lemma without simple papillae (Fig. 1H–J); bicellular microtrichomes absent; unicellular macrotrichomes absent. Palea with simple papillae absent (Fig. 1K–M); bicellular microtrichomes absent; unicellular macrotrichomes absent.

 Phylogenetic analysis

The trees resulted from the BI and ML analysis were mostly congruent in the major clades sampled, with the representative specimens of the tribes Andropogoneae and Paspaleae, the seven subtribes of Paniceae and the “Sacciolepis grex” clade all forming moderate to strong-supported clades (Fig. 2). The exception is in the Panicinae subtribe, which was recovered with strong-supported values (BS 100; PP 1), but the genus Louisiella C.E.Hubb & J.Léonard was embedded within Panicum s.str., in a group with Panicum australiense Domin and Panicum seminudum Domin (BS 49; PP 0.93). We chose to display the majority-rule consensus tree from the BI analysis (Fig. 2) to represent the topology of our dataset, with BS values from the ML analysis added on the branches as well. The complete separated trees of the BI and ML analyses are available as Suppl. materials 4 and 5.

10.5091/plecevo.185113.figure2 EDB03F07-8190-5AD2-BDE2-B5D97DCF3194

Majority-rule consensus tree from the Bayesian inference (BI) analysis of the combined dataset (ndhF+rbcL). Nodes support values on the left represent ML bootstrap support (BS) and on the right represent BI posterior probabilities (PP). Trichanthecium ambositrense highlighted in bold.

https://binary.pensoft.net/fig/1704803

The “Sacciolepis grex” clade forms a strongly supported group (BS 87; PP 0.98), in a polytomy of two clades and three non-Kranz Panicum species (P. gardneri Thwaites, P. notatum Retz., and P. trichanthum Nees). The first clade (BS 60; PP 0.98) is strong supported in the BI analysis and represent 14 non-Kranz Panicum species, including representative specimens of P. sect. Monticola Stapf, P. sect. Ovalifolia Stapf, and former P. sect. Parvifolia; within this clade, one strong-supported group (BS 86; PP 0.98) is presented with two subclades: the first one (BS 95; PP 1) is formed by the American species P. hirtum Lam. and an unresolved group (BS 86; PP 0.97) with one eastern African species (P. glandulopaniculatum Renvoize) and the pantropical P. brevifolium L. and the second one (BS 79; PP 0.99) is formed by the African species P. capuronii A.Camus, P. heterostachyum Hack., P. issongense Pilg., and P. subhystrix A.Camus.

The second clade correspond to the Kellochloa, P. bisulcatum + Sacciolepis, and Trichanthecium group (BS 74; PP 0.96); Kellochloa was recovered with high support (BS 94; PP 0.99) as sister group to P. bisulcatum + Sacciolepis and Trichanthecium (BS 32; PP 0.77); P. bisulcatum Thunb. (BS 94; PP 0.99) is recovered as sister species to the Sacciolepis clade (BS 93; PP 0.93), and the Trichanthecium clade is presented with moderate-low support (BS 32; PP 0.78).

Panicum ambositrense was placed within the Trichanthecium clade in a strongly supported group with T. perrieri (BS 97; PP 1), and the two form a well-supported clade with T. aequinerve (Nees) Zuloaga (BS 99; PP 1). Trichanthecium hochstetteri (Steud.) Zuloaga is sister to the three species (BS 55; PP 0.87) and they form a highly supported group in the BI analysis (BS 58; PP 0.99) with a clade formed by T. acrotrichum (Hook.f.) Zuloaga, T. calvum (Stapf) Zuloaga, T. chionachne (Mez) Zuloaga, T. eickii (Mez) Zuloaga, and T. inaequilatum (Stapf & C.E.Hubb.) Zuloaga (BS 65; PP 0.99). The relationship between the other Trichanthecium species sampled was recovered with moderate to low support in both analyses, apart from three groups: a well-supported clade is formed by T. gracilicaule (Rendle) Zuloaga & Morrone, T. margaritiferum (Chiov.) Zuloaga & Morrone, T. marunguensis Zuloaga, and T. natalense (Hochst.) Zuloaga & Morrone (BS 97; PP 1); T. brazzavillense (Franch.) Zuloaga & Morrone and T. tenellum (Lam.) Zuloaga & Morrone form a highly supported clade (BS 100; PP 1), but the relationship between the two species is unresolved; and the northern South American species (T. arctum (Swallen) Zuloaga & Morrone, T. granuliferum (Kunth) Zuloaga & Morrone, T. micranthum (Kunth) Zuloaga & Morrone, T. pyrularium (Hitchc. & Chase) Zuloaga & Morrone, and T. rivale (Swallen) Zuloaga & Morrone) form a highly supported clade (BS 83; PP 0.99).

 Discussion Anatomical and micromorphological analysis

The cross-section analysis showed that P. ambositrense possess two sheaths without specialized chloroplasts surrounding the vascular bundles (Fig. 1D) and exhibit six to ten mesophyll cells with specialized chloroplasts between consecutive vascular bundles (Fig. 1E–F). These characteristics are present in plants with non-Kranz anatomy and indicative of C3 photosynthesis (Brown 1977; Ellis 1977; Hattersley 1988; Hattersley and Watson 1992). Our results are consistent with the expected leaf anatomical structure for Trichanthecium and for the “Sacciolepis grex” clade (De Gennaro et al. 2010; Zuloaga et al. 2011, 2024; Nicola et al. 2015). In addition, this structure can be used to differentiate P. ambositrense from Panicum s.str., which has all species with C4 photosynthesis, subtype NAD-me (Zuloaga et al. 2018). The epidermis analysis showed the presence of dumbbell- and saddle-shaped silica bodies in the costal zones of both surfaces (Fig. 1A, C), as well as prickles (Fig. 1B) in the adaxial surface and bicellular microtrichomes in the abaxial surface (Fig. 1C). This result is in accordance with the epidermis described for Trichanthecium marunguensis (Zuloaga et al. 2024), which is the only species of the genus with a complete description of leaf anatomy; an in-depth study of leaf anatomy in Trichanthecium is necessary to evaluate characteristics that can be used to differentiate the species.

The upper anthecium surface of P. ambositrense is completely smooth and glabrous (Fig. 1J–L), which is also the case in 11 other African Trichanthecium species, including the morphologically similar T. perrieri (Zuloaga et al. 2024). This character, however, can be found in several species of Panicum s.l. (Aliscioni et al. 2003; Zuloaga et al. 2018) and is therefore not taxonomically diagnostic. Trichanthecium (whose name refers to the presence of bicellular microtrichomes on the surface of the upper anthecium) has been described as having the upper anthecium ornamentation (also including evenly distributed simple papillae and sometimes macrotrichomes at the apex) present in all species (Zuloaga et al. 2011). Further studies have shown that, in addition to the 11 African species with glabrous upper anthecium, the distribution of simple papillae ornamentation, the presence of unicellular macrotrichomes, and the distribution, size, and shape of bicellular microtrichomes vary among the remaining species (Zuloaga et al. 2011, 2024; Xanthos et al. 2020). In the “Sacciolepis grex” clade, these types of upper anthecium ornamentation are also found in several taxa. This group is composed of Kellochloa, Sacciolepis, Trichanthecium, and 17 Panicum s.l. species that have similar overall morphologies, apart from Sacciolepis, which has prevented these species from being treated as a single genus; additionally, other morphological and molecular data supports Kellochloa and Trichanthecium as distinct genera within the clade (Zuloaga et al. 2011, 2024; Nicola et al. 2015).

 Phylogenetic analysis

Both phylogenetic analyses recovered P. ambositrense within Trichanthecium, in the “Sacciolepis grex” clade in the tribe Paniceae. The species was placed in a strongly supported group with T. perrieri, a morphological similar species also endemic to Madagascar (Zuloaga et al. 2024). The two species are morphologically similar to the eastern African species T. aequinerve, which was recovered with the aforementioned species. This result is in accordance with Hackel et al. (2018), although this group was placed as a sister clade to Trichanthecium and not embedded in the genus, such as in Zuloaga et al. (2024). In the latter study, P. ambositrense was not included, but T. aequinerve and T. perrieri formed a strongly supported group, and both were moderately to strongly supported together with T. hochstetteri. In our analysis, this topology was also observed (Fig. 2).

Although the subtribes sampled form monophyletic clades in accordance with recent phylogenies of these groups (Acosta et al. 2014; Scataglini et al. 2014a; Soreng et al. 2022; Delfini et al. 2023a, 2023b), the relationships within the subtribe Panicinae are unresolved in our analysis (Fig. 2). The genus Louisiella, considered as a sister group of Panicum s.str. (sensu Zuloaga et al. 2018), was recovered embedded within Panicum s.str.; however, the species of the sections of Panicum s.str. sampled did not form monophyletic groups – except for Panicum sect. Rudgeana (P. cervicatum Chase ex Luces, P. ligulare Nees ex Trin., and P. virgatum L.) – and several clades had low to moderate support in the ML analysis (Fig. 2; Suppl. material 5). This discrepancy in the topology of the Panicinae clade was also observed in previous publications (Morrone et al. 2012; Hackel et al. 2018) and probably resulted from the markers and number of species used. Nevertheless, the subtribe Panicinae was recovered with high support and all 19 species of Panicum s.l. (including P. ambositrense) were grouped outside of the Panicinae clade, in the “Sacciolepis grex” clade, as observed previously (Zuloaga et al. 2011, 2018; Morrone et al. 2012; Nicola et al. 2015; Hackel et al. 2018).

The 14 non-Kranz Panicum species grouped in the “Sacciolepis grex” clade (Fig. 2) were represented with high support in the BI analysis, but were not presented with a defined morphological synapomorphy in the analysis of Zuloaga et al. (2018). Furthermore, the representative species of P. sect. Monticola (P. monticola Hook.f., P. millegrana Poir., P. sellowii Nees, and P. trichoides Sw.), P. sect. Ovalifolia (P. brevifolium and P. heterostachyum), and former P. sect. Parvifolia (P. bartlettii Swallen, P. hirtum Lam., and P. trichanthum Nees) did not form monophyletic groups. It is worthwhile to mention that most of these species are represented with only a ndhF marker accession, which might explain the low support values and unresolved position of the clades. An in-depth study of these species is necessary to propose taxonomic changes. Meanwhile, the topology of the Kellochloa, P. bisulcatum + Sacciolepis, and Trichanthecium clades were congruent with previous phylogenies (Nicola et al. 2015; Zuloaga et al. 2018, 2024). Thus, in order to render Trichanthecium monophyletic, and with the anatomical and morphological data gathered corroborating the phylogenetic position of P. ambositrense, we formerly propose a new combination.

 Taxonomic treatment Plantae Poales Poaceae 2ABB3609-89DB-564F-A45B-F59E5DE0CBCA Trichanthecium ambositrense urn:lsid:ipni.org:names:77382043-1 (A.Camus) Lopes-Neto, P.L.Viana & Zuloaga comb. nov. Figs 1 , 2 , 3 , 4 ; Tables 1 –2 Panicum ambositrense A.Camus, Bulletin de la Société Botanique de France 72: 370. 1925. (Camus 1925) Type

MADAGASCAR – Fianarantsoa province • Env. D’Ambositra; [20°32’10.5”S, 47°14’45.5”E]; 1700 m; May 1912; J.M.H.A. Perrier de la Bâthie 10851 “no. 34”; lectotype (designated by Vorontsova 2018: 148): P [P00450276]; isolectotype: K [K00805604] image.

 Description

Perennials. Rhizomes absent. Culms 40–200 cm tall, prostrate, rooting at the lower nodes, branching at the lower and upper nodes, internodes 4–5.5 cm long, glabrous; nodes black (in siccus), glabrous. Leaves regularly distributed along the culms; sheaths 2.5–5 cm long, shorter than the internodes, glabrous, not distichous and not overlapping, glabrous on both margins; ligules 0.2–0.6 mm long, membranous, shortly ciliate at the apex, truncate, yellowish (in siccus); pseudoligules absent; auricles absent; blades 5–13 × 0.3–1 cm, linear or linear-lanceolate, flat, horizontal to ascended, green (in siccus), glabrous or pubescent on both surfaces, base rounded, not amplexicaul, margins scaberulous, apex acuminate. Synflorescence terminal, exserted; peduncle 8–10 cm long, scaberulous; panicle 10–25 × 5–8 cm, diffuse; main axis sinuous, scaberulous; pulvini glabrous; first order branches alternate, ascended, not falling together with the spikelets at maturity; axis of the branches glabrous; pedicels 3–5 mm long, yellowish (in siccus), scaberulous, sinuous, not curved at maturity, claviform. Spikelets 2–2.5(–2.7) × 0.6–0.8 mm, narrowly ovoid, green or purple, glabrous, perpendicularly inserted on their pedicels, not curved at maturity; lower glume 2–2.5(–2.7) mm long, as long as the spikelet, not embracing the upper glume at its base, narrowly ovate, 3-nerved, apex acuminate; stipe between the glumes absent; upper glume 2–2.5(–2.7) mm long, narrowly ovate, 5–7-nerved, apex acuminate; lower lemma 2–2.5(–2.7) mm long, elliptic, 5-nerved, apex apiculate; lower palea present, 1.2–1.6 mm long, lanceolate, white (in siccus), glabrous, apex acute; lower flower sterile; upper anthecium stipe absent; upper anthecium 1.3–1.5 × 0.5–0.6 mm, ellipsoid, whitish (in siccus), smooth, glabrous, apex rounded. Caryopsis not seen.

 Distribution

Trichanthecium ambositrense occurs in the central and northern regions of Madagascar, while a single collection originates from Grande Comoros island (Comoros) (Fig. 3).

10.5091/plecevo.185113.figure3 ACD19646-125C-5383-9432-50307D033F79

Geographic distribution of Trichanthecium ambositrense.

https://binary.pensoft.net/fig/1704804 Habitat and ecology

Found near streams in wet gallery forest understory, at (517–)1253–2244 m elevation.

 Phenology

Flowering from September to June.

 Preliminary IUCN conservation assessment

Trichanthecium ambositrense has an EOO of 400,824 km2 and AOO of 56 km2. According to the IUCN criteria (2024), this species is assessed as Vulnerable VU B2ab(iii), based on the AOO (< 2,000 km2), the number of locations (< 10) (including five protected areas in Madagascar, i.e. Analamazaotra National Park, Andringitra National Park, Mahomborondro National Park, Massif d’Itremo National Park, and Montagne d’Ambre National Park), and the inferred continuous decline of habit quality (Andrianambinina et al. 2025; Rakotonasolo et al. 2025).

 Notes

Trichanthecium ambositrense can be recognized by the combination of the following morphological characters: perennial life cycle, prostrate culms, rooting at the lower nodes and branching at the lower and upper nodes, blades linear or linear-lanceolate, the exserted synflorescences, panicles 10–25 × 5–8 cm, diffuse, bearing narrowly ovoid spikelets, 2–2.5(–2.7) mm long, glabrous, with apex acuminate, lower glume as long as the spikelet, the lower palea present but smaller than the lower lemma, and lower flower sterile (Fig. 4). Trichanthecium perrieri, a closely related species and also endemic to Madagascar (Zuloaga et al. 2024), is often confused with T. ambositrense, since both species possesses prostrate culms, rooting at the lower nodes, leaves regularly distributed along the culms, linear or linear-lanceolate blades, synflorescence terminal, narrowly ovoid spikelets, and lower glume acuminate, but T. perrieri can be mainly distinguished by the larger spikelets, 2.5–3(–3.2) mm long, and the shorter and contracted panicles, 2–7 × 2–6 cm (Table 1).

10.5091/plecevo.185113.figure4 75D59ED2-1E8B-5106-BBB3-27B68F70CB92

Illustration of Trichanthecium ambositrense. A. Habit. B. Detail of a branch of the synflorescence. C. Spikelet. D. Lower glume. E. Upper glume. F. Lower lemma. G. Lower palea. H. Upper anthecium, upper palea view. I. Upper anthecium, upper lemma view. Based on J.M.H.A. Perrier de la Bâthie 16365 (P02251335, P02251348). Drawn by R.B. Lopes-Neto.

https://binary.pensoft.net/fig/1704805

Morphological comparison between Trichanthecium ambositrense and closely related species.

Characters T. ambositrense T. aequinerve T. perrieri T. pusillum
Life cycle Perennials Annuals Perennials Annuals
Habit Prostrate Decumbent Prostrate Decumbent
Culms branching Branching at the lower and upper nodes Branching at the lower nodes Branching at the lower nodes Branching at the lower nodes
Blades shape Linear or linear-lanceolate Narrowly lanceolate Linear or linear-lanceolate Ovate-lanceolate
Synflorescence Exserted Exserted Exserted or partially included in the upper leaves Shortly-exserted
Panicles size (cm) 10–25 × 5–8 4–15(–20) × 4–15 2–7 × 2–6 1–2(–4.5) × 1–3
Panicle branches Diffuse Diffuse Contracted Contracted
Spikelets length (mm) 2–2.5(–2.7) 2.5–3 2.5–3(–3.2) 1.5–2
Spikelets shape Narrowly ovoid Narrowly ovoid Narrowly ovoid Ellipsoid
Spikelets indumentum Glabrous Pubescent Glabrous or finely pubescent Hirsute, with tuberculate trichomes
Spikelets apex Acuminate Acute Acuminate Acute
Lower glume length (mm) 2–2.5(–2.7) 2.5–3 2.5–3(–3.2) 1.2–1.5
Lower glume length relative to the spikelet As long as the spikelet As long as the spikelet As long as the spikelet 1/2 to 4/5 the length of the spikelet
Lower glume shape Narrowly ovate Ovate Narrowly ovate Elliptic
Lower glume number of nerves 3 3(–5) 3–5 3
Lower palea length (mm) 1.2–1.6 2.4–2.6 ca 0.4 Absent
Lower palea length relative to the lower lemma Shorter than the lower lemma Shorter than the lower lemma Shorter than the lower lemma -
Lower flower Sterile Staminate or sterile Sterile Sterile

Both species are morphologically similar to T. aequinerve, an African species widely distributed from Ethiopia to South Africa (Zuloaga et al. 2024), which can be differentiated by the decumbent culms and lower glume ovate with apex acute (Table 1). Trichanthecium pusillum (Hook.f.) Zuloaga, an annual species widely distributed on east tropical Africa, from Ethiopia to Tanzania (Zuloaga et al. 2024), can be differentiated by the decumbent culms, short-exserted panicles, 1–2(–4.5) × 1–3 cm, the hirsute ellipsoid spikelets with acute apex, lower glume 1/2 to 4/5 the length of the spikelet and lower palea absent (Table 1).

In addition to T. ambositrense and T. perrieri, there are two other Trichanthecium species recorded in Madagascar: Trichanthecium brazzavillense and Trichanthecium parvifolium (Lam.) Zuloaga & Morrone (Vorontsova 2018). Trichanthecium brazzavillense is mainly distinguished from the aforementioned congeners by the erect unbranched culms, not rooting at the lower nodes, filiform blades, synflorescences bearing globose or broadly ellipsoid spikelets, densely hirsute with tuberculate trichomes, with apex acute and lower palea as long as the lower lemma, while T. parvifolium it is an annual decumbent and geniculate herb, rooting and branching at the lower nodes, with ovate-lanceolate blades, synflorescences bearing globose spikelets, 1–1.8 mm long, glabrous, with apex obtuse or acute and lower palea shorter than the lower lemma (Table 2).

Morphological comparison between the Trichanthecium species registered in Madagascar.

Characters T. ambositrense T. brazzavillense T. parvifolium T. perrieri
Life cycle Perennial Perennial Annual Perennial
Habit Prostrate Erect Decumbent and geniculate Prostrate
Culms rooting Rooting at the lower nodes Not rooting at the lower nodes Rooting at the lower nodes Rooting at the lower nodes
Culms branching Branching at the lower and upper nodes Unbranched Branching at the lower nodes Branching at the lower nodes
Blades shape Linear or linear-lanceolate Filiform Ovate-lanceolate Linear or linear-lanceolate
Synflorescence exserted or partially included in the upper leaves Exserted Exserted Exserted or partially included in the upper leaves Partially included in the upper leaves or exserted
Panicles sizes (cm) 10–25 × 5–8 3–14 × 2–10 1–6 × 0.7–5 2–7 × 2–6
Panicle branches Diffuse Diffuse to contracted Diffuse to contracted Contracted
Spikelets length (mm) 2–2.5(–2.7) 1.2–1.6 1–1.8 2.5–3(–3.2)
Spikelets shape Narrowly ovoid Globose or broadly ellipsoid Globose Narrowly ovoid
Spikelets indumentum Glabrous Densely hirsute, with tuberculate trichomes Glabrous Glabrous or finely pubescent
Spikelets apex Acuminate Acute Obtuse or acute Acuminate
Lower glume length (mm) 2–2.5(–2.7) 1.1–1.3 0.8–1.2 2.5–3(–3.2)
Lower glume length relative to the spikelet As long as the spikelet 3/4 to 4/5 the length of the spikelet 3/4 the length of the spikelet As long as the spikelet
Lower glume shape Narrowly ovate Ovate Ovate Narrowly ovate
Lower glume number of nerves 3 3 3 3–5
Lower palea length (mm) 1.2–1.6 1.2–1.6 ca 0.9 ca 0.4
Lower palea length relative to the lower lemma Shorter than the lower lemma As long as the lower lemma Shorter than the lower lemma Shorter than the lower lemma
Lower flower Sterile Staminate Staminate Sterile
Additional material examined.

COMOROS – Grande Comoros • “Iles Comoros”; [11°35’10”S, 43°19’59”E]; 57m; 1847–1852; L.H. Boivin s.n.; P [P00216552, P02332660].

MADAGASCAR – Antananarivo province • Ambatolaona; 15 May 1935; Herbarium Jardin Botanique de Tananarive 32423; P [P02251336], TAN n.v. • Ambatovory (environs de Tananarive; P.K. 26 route de Tamatave); Apr. 1957; J.M. Bosser 11009; P [P02251345] • Angavokely; Mar. 1959; J.M. Bosser 12730; TAN • Analamisaraka; 19°13’12.79”S, 47°09’39.02”E; 1768 m; 6 Mar. 2022; N.H. Rakotomalala, N.F. Randrianarimanana, L. MacKinnon & J.A. Randriamampianina 552; K • Angavokely (east of Tananarive); 25 Jun. 1964; T. Tateoka 3519; P [P02726869] • Angavokely, station menant a l’Angavobe, station forestière Angavokely; Jan. 1960; J.M. Bosser 13719; TAN • Ankaratra, Centre; 2000 m; Apr. 1914; J.M.H.A. Perrier de la Bâthie 10740; P [P02251347] • Ankaratra, Faratsiho, Faratsiho; Jan. 1955; J.M. Bosser 7621; P [P02307398], TAN • Ankaratra, Manjakatompo; Feb. 1953; J.M. Bosser 4850; P [P02251340] • Antsirabe, forest of Manjakatompo; 24 May 1950; R.E. Vaughan s.n.; K [K000805440] • La Mandraka; Feb. 1953; J.M. Bosser 5008; TAN • La Mandraka; Feb. 1953; J.M. Bosser 5009; P [P02251334] • Manerinerina, Analamaintso forest, 10–20 km after Manerinerina; 17°57’31”S, 47°07’30”E; 1472 m; 13 Feb. 2013; M. Vorontsova, G. Besnard, H. Ralimanana & J. Razanatsoa 907; K, TAN • Manjakatompo; Feb. 1953; J.M. Bosser 4853; TAN • Ramainandro; 1600 m; Feb. 1957; J.M. Bosser 10817; P [P02251341], TAN. – Antsiranana province • Diana Region, montagne d’Ambre PN, near sommet d’Ambre; 12°35’S, 49°09’E; 1253 m; 9 Apr. 1993; O. Andrianantoanina, S.T. Malcomber, A. Solotiana & J. Rabety 49; G [G00393756], K [K000805443], MO [MO2973764, MO3065146], P [P06795995], S [S16-18279], TAN [TAN101817997], US [US04303282] • Massif de Marivorahona au SW de Manambato; [13°42’S, 49°07’E]; 1750–2244 m; 18 Mar. 1951; H. Humbert & R. Capuron 25692; K [K000805552], MO [MO3120266], P [P01914209, P01914213, P02726977], TAN • Plantes du Parc National de la Montagne d’Ambre, montagne d’Ambre, partie centrale (12°34’S – 49°10’E) à 430 m du point Côté 1445, au 267°; 12°35’47”S, 49°09’34”E; 1344 m; 10 Nov. 2007; L. Gautier & L. Nusbaumer LG5188; BR [BR0000025908978V], G [G00075803], K [K001634952] • Tsaratanana Massif, trail from Mangindrano up S ridge of the Moromokotro, Andohinisambirano to Rahampintso Marqina, Elfin forest; 1800–2000 m; 11 May 1974; A.H. Gentry 11674; K [K000805441], P [P02251342] • Tsaratanana; 2000 m; Apr. 1923; J.M.H.A. Perrier de la Bâthie 16365; P [P02251335, P02251348]. – Fianarantsoa province • 34 km N of Fianarantsoa, PK 376 along route 7; 28 Jan. 1975; T.B. Croat 29960; TAN • Ambatomaneloka, Ambatomaneloka (Itremo), PK 121 route de Morondava; Sep. 1956; J.M. Bosser 9949; TAN • Ambohimitombo, Ambohimitombo forest (Tanala); [20°43’05.5”S, 47°25’44.7”E]; 1350–1440 m; 1 Jan. 1895; C. Forsyth-Major 267; K [K000805605] • Andringitra National Park; [22°12’49.05”S, 46°55’20”E]; Apr. 1964; J.M. Bosser 19435; P [P02251332, P03487900], TAN • Est-Andringitra, Anjavidilava, Versant Est; [22°12’49.05”S, 46°53’20”E]; 1700 m; 11 Jan. 1971; J.L. Guillaumet 3701; P [P02325400], TAN • Itremo, Antsirakambiaty, à l’entrée de la première forêt galerie d’Antsirakambiaty; 20°35’47”S, 46°33’45”E; 1534 m; 18 Feb. 2014; O.P. Nanjarisoa, H. Ralimanana & A. Razafindraibe 138; K, TAN • Itremo, Antsirakambiaty, Itremo Protected Area; 20°35’42”S, 46°33’47.1”E; 1524 m; 12 Mar. 2012; M. Vorontsova G. Ratovonirina, F. Rakotonasolo, R. Rajaonarison, R. Andriamampionona & Rakoton 736; K, TAN. – Mahajanga province • Betainkankana, Ankaizina; [14°18’S, 48°40’E]; May 1962; J.M. Bosser 2536; TAN. – Toamasina province • Analamazaotra; [18°56’19.8”S, 48°26’55”E]; J.M.H.A. Perrier de la Bâthie 10922; K [K000244679], P [P02251343] • Analamazaotra; Apr. 1914; J.M.H.A. Perrier de la Bâthie 10925; K [K000805442], P [P02251337], TAN • Périnet; [18°55’39.32”S, 48°24’51.66”E]; Feb. 1955; J.M. Bosser 7775; P [P02251338] • Périnet, forest reserve in vicinity of Périnet, along Route 2 between Tananarive and Tamatave; 25 Feb. 1975; T.B. Croat 32262; TAN • without locality; Oct. 1936; Herbarium Jardin Botanique de Tananarive 2166; P [P02251346].

Key to the Old World species of <italic><tp:taxon-name><tp:taxon-name-part taxon-name-part-type="genus" reg="Trichanthecium">Trichanthecium</tp:taxon-name-part></tp:taxon-name></italic> (adapted from <xref ref-type="bibr" rid="B68">Zuloaga et al. 2024</xref>)

Terminology according to Zuloaga et al. (2011).

1. Stipe between glumes present T. mueense
– Stipe between glumes absent 2
2. Lower glume with two tuberculate trichomes at the apex T. marunguensis
– Lower glume glabrous or pilose, without two tuberculate trichomes at the apex 3
3. Perennials; culms erect, not decumbent 4
– Annuals or perennials; culms decumbent or prostrate 13
4. Blades filiform, 1–2 mm wide 5
– Blades linear, lanceolate or ovate-lanceolate, (2–)3–11 mm wide 6
5. Blades 8–25 cm long; spikelets 2–2.4 mm long, glabrous T. natalense
– Blades 1–4 cm long; spikelets 1.3–1.5 mm long, sparsely papillose-pilose, occasionally glabrous T. filifolium
6. Upper anthecium (floret) glabrous 7
– Upper anthecium (floret) with bicellular microtrichomes on its surface 9
7. Spikelets with glumes and lower lemma glabrous T. eickii
– Spikelets with glumes and lower lemma pilose 8
8. Blades lanceolate, 3–6 mm wide, flat, subcordate at the base; spikelets 2–2.7 mm long T. inaequilatum
– Blades linear, 2(–3) mm wide, involute, narrowed at the base; spikelets 3–3.5 mm long T. striatissimum
9. Leaves mainly concentrated at the base of the culms; upper anthecium (floret) with elongated bicellular trichomes, the distal cell elongated T. brazzavillense
– Leaves regularly distributed along the culms; upper anthecium (floret) with globose bicellular trichomes, the distal cell globose 10
10. Broadly ellipsoid spikelets 11
– Ellipsoid spikelets 12
11. Blades lanceolate; spikelets 1.8–2.2 mm long T. praealtum
– Blades linear-lanceolate; spikelets 1.5–1.7 mm long T. strictissimum
12. Blades lanceolate; spikelets 2.4–3 mm long; upper anthecium (floret) narrowly ellipsoid T. margaritiferum
– Blades linear-lanceolate; spikelets (1.6–)2–2.2(–2.4) mm long; upper anthecium (floret) broadly ellipsoid T. nervatum
13. Upper glume with whitish trichomes 3–4 mm long toward the apex T. acrotrichum
– Upper glume glabrous, if pilose shortly hairy and without trichomes 3–4 mm long at the apex 14
14. Lower glume 1/6 to 1/4 times the length of the spikelet, nerveless; upper glume aristate, awn up to 1 mm long T. delicatulum
– Lower glume (1/4–)1/2 times to as long as the spikelet, (1–)3–5-nerved; upper glume acute to acuminate, not aristate 15
15. Blades cordate and amplexicaul at the base 16
– Blades attenuate, rounded or subcordate, not amplexicaul, at the base 18
16. Spikelets 1.6–1.9 mm long; lower flower staminate; upper anthecium (floret) with globose bicellular trichomes T. dinklagei
– Spikelets 2–2.5 mm long; lower flower staminate or sterile; upper anthecium (floret) glabrous 17
17. Lower glume 1/2 to 2/3 times the length of the spikelet, 1–3-nerved, acute; lower palea absent T. calvum
– Lower glume 1/4 to 1/3 times the length of the spikelet, nerveless to 1-nerved, obtuse to acute; lower palea present T. wiehei
18. Lower palea reduced or absent; lower flower sterile 19
– Lower palea almost as long as the lower lemma; lower flower staminate 21
19. Annuals; decumbent culms; spikelets ellipsoid, apex acute; lower glume 1/2 to 4/5 the length of the spikelet T. pusillum
– Perennials; prostrate culms; spikelets narrowly ovoid, apex acuminate; lower glume as long as the spikelet 20
20. Blades linear or linear-lanceolate; panicles 10–25 × 5–8 cm, diffuse; spikelets 2–2.5(–2.7) mm long T. ambositrense
– Blades linear; panicles 2–7 × 2–6 cm, contracted; spikelets 2.5–3(–3.2) mm long T. perrieri
21. Spikelets 1–2.4 mm long; upper anthecium (floret) with globose bicellular trichomes 22
– Spikelets 2.2–3 mm long; upper anthecium (floret) glabrous 26
22. Blades linear-lanceolate, narrowed at the base 23
– Blades ovate to ovate-lanceolate, subcordate at the base 24
23. Spikelets 1–1.8 mm long, papillose-pilose with long tuberculate trichomes T. tenellum
– Spikelets 2–2.4 mm long, glabrous T. gracilicaule
24. Spikelets with tuberculate trichomes T. tenerium
– Spikelets glabrous or pilose, but without tuberculate trichomes 25
25. Spikelets ellipsoid, the upper glume and lower lemma acuminate; upper anthecium (floret) 0.6–1 mm long, shorter than the spikelet T. glaucocladum
– Spikelets globose, the upper glume and lower lemma obtuse; upper anthecium (floret) 1.1–1.8 mm long, almost as long as the spikelet T. parvifolium
26. Spikelets pilose 27
– Spikelets glabrous 28
27. Spikelets narrowly ovoid, 2.5–3 mm long; lower glume almost as long as the spikelet T. aequinerve
– Spikelets oblong in outline, 2.2–2.5(–2.6) mm long; lower glume 2/3 to 3/4 the length of the spikelet T. hochstetteri
28. Spikelets narrowly ovoid, glabrous T. chionachne
– Spikelets oblong in outline, sparsely pubescent, rarely glabrous T. hochstetteri
Conclusion

We evaluated the position of Panicum ambositrense in the “Sacciolepis grex” clade of the tribe Paniceae. Using an integrative approach of phylogenetic, anatomical, and morphological analyses, we confirmed that this species is included in the Trichanthecium clade, has photosynthesis C3 and is in conformity with the morphological concept of the genus. Consequently, we made a new combination: Trichanthecium ambositrense. This species occurs in Madagascar and has a single collection in Comoros and is assessed by us as Vulnerable (VU).

 Data availability

The data underpinning the analysis reported in this paper are deposited at Zenodo: https://doi.org/10.5281/zenodo.20070710.

 Acknowledgements

This study was financed in part by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - Brasil (CAPES) - Finance Code 001. This paper is part of the RBLN’s PhD thesis at the Museu Paraense Emílio Goeldi and Universidade Federal Rural da Amazônia (Belém, Brazil). This paper was partially funded by the Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) project “Origens da flora amazônica: biogeografia de linhagens de plantas com flores” [grant number 422191/2021-3]. RBLN thanks the Programa Reflora/Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)/Jardim Botânico do Rio de Janeiro (JBRJ) [grant number 200333/2023-2] for the PhD stay scholarship. We thank the Royal Botanic Gardens, Kew for providing the samples of leaves and spikelets for the analyses conducted. We thank Hilton Tulio Costi and the Laboratório Institucional de Microscopia Eletrônica of MPEG for the assistance during the SEM sessions and the institutional support. We thank Miantsa Andrianantenaina and Nantenaina Herizo Rakotomalala for their help with the specimens deposited at the TAN herbarium. RBLN thanks the Natural History Museum of Vienna (Vienna, Austria) for the institutional support during the PhD stay. RBLN thanks Arianne Flexa de Castro, Caroline Oliveira Andrino, Juliene de Fátima Maciel da Silva, Lucas Ferreira Colares, Rafael Barbosa Gomes da Silva, and Vanessa Lino de Lima for their suggestions. We also thank the editors and reviewers for their thoughtful contributions to the paper.

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Phytotaxa 646(3): 230–264. https://doi.org/10.11646/phytotaxa.646.3.2 Supplementary materials 10.5091/plecevo.185113.suppl1 B08C3826-F7C7-5AD9-A9A2-44E8C9B861FB

List of species, vouchers and GenBank accessions utilized for phylogenetic analysis.

 https://binary.pensoft.net/file/1704806 10.5091/plecevo.185113.suppl2 FF20F21D-98D2-5CFD-BBC6-94FC2598785B

List of species and vouchers examined to produce taxonomic comparisons.

 https://binary.pensoft.net/file/1704807 10.5091/plecevo.185113.suppl3 9F5E95FB-1A9A-5E20-88F0-15A6DA19097F

List of vouchers and coordinates used in the preparation of the distribution map.

 https://binary.pensoft.net/file/1704808 10.5091/plecevo.185113.suppl4 F01E18D7-FEA1-50E4-8863-9497D250D1C3

Majority-rule consensus full tree from the Bayesian inference (BI) analysis of the combined dataset (ndhF+rbcL). Trichanthecium ambositrense highlighted in bold.

 https://binary.pensoft.net/file/1704809 10.5091/plecevo.185113.suppl5 5D0D58BA-96D6-5DF8-96B2-DCF9DE38AB2C

Best-scoring tree of the Maximum likelihood (ML) analysis of the combined dataset (ndhF+rbcL). Trichanthecium ambositrense highlighted in bold.

 https://binary.pensoft.net/file/1704810