KOENEN, E.J.M. (2024). A new species of Mimosa (Leguminosae) endemic to Central Madagascar. Candollea 79: 229–234. In English, English and French abstracts. DOI: http://dx.doi.org/10.15553/c2024v792a2
A new species of Mimosa L. (Leguminosae: Caesalpinioideae) from Madagascar is described and illustrated. The species is known only from the Massif d'Ibity and surrounding area in the Central Highlands, where it occurs in the understory of Tapia forest. Its morphological affinities to similar Malagasy species are discussed and a key to identify them is included.
KOENEN, E.J.M. (2024). Une nouvelle espèce de Mimosa (Leguminosae) endémique du centre de Madagascar. Candollea 79: 229–234. En anglais, résumés anglais et français. DOI: http://dx.doi.org/10.15553/c2024v792a2
Une nouvelle espèce de Mimosa L. (Leguminosae: Caesalpinioideae) de Madagascar est décrite et illustrée. L'espèce n'est connue que du Massif d'Ibity et de ses environs dans les Hautes Terres centrales, où elle se trouve dans le sous-bois de la forêt de Tapia. Les affinités morphologiques avec les espèces similaires malgaches sont discutées et une clé d'identification est incluse.
Introduction
Mimosa L. (Leguminosae) is one of the three genera placed in the Mimosa clade (along with Adenopodia C. Presl and Piptadenia Benth.), a subclade of the tribe Mimoseae in the subfamily Caesalpinioideae (previously referred to as the mimosoid clade, which broadly coincides with the formerly recognized subfamily Mimosoideae) (Koenen et al., 2020; Borges et al., 2024; Queiroz et al., 2024). The genus is nearly pantropical in its distribution but over 570 of the c. 615 species occur in the Americas with notable centers of diversity in Brazil and Mexico (Barneby, 1991; Borges et al., 2024), while the species from Africa, Asia, and Madagascar form a clade that is deeply nested among New World lineages in the phylogeny of the genus (Simon et al., 2011).
During fieldwork in Madagascar in January 2014, a shrub which can be referred to the genus Mimosa was collected and found to represent an undescribed species. Further collections of this same taxon were located in the herbarium of the Musée national d'Histoire naturelle in Paris. All collections are from mid-elevation Tapia forest vegetation.This vegetation type is named after the vernacular name of the dominant tree species of these forests, Uapaca bojeri Baill. (Phyllanthaceae), which typically forms an evergreen canopy with sclerophyllous ericoid shrubs dominating the understory (Moat & Smith, 2007) (Fig. 1F). Two endemic Malagasy plant families, Asteropeiaceae and Sarcolaenaceae, are also characteristic of this vegetation that is typically found at elevations ranging from 500–1800 m. Substantial areas of Tapia forest are found in Isalo, Ambatofinandrahana, Ibity, and Morarano, but it has been estimated that this vegetation type has been reduced by 43% since 1970 (Moat & Smith, 2007).The discovery of this species new to science highlights the occurrence of rare narrowly endemic and even undescribed species in these forests and their conservation value and importance.
The new species has been sampled in a phylogenetic analysis by Ringelberg et al. (2023), where a subtree of their metachronogram for the Old World species of Mimosa was inferred from RADseq data. The species was recovered with full support (1.0 PP) as the sister species of a fully supported clade of six species including M. vilersii Drake, M. menabeensis R. Vig., and M. dumetaria Villiers. These results lend further support to the need of describing this taxon as a new species. Since Villiers' treatment of the genus Mimosa for Madagascar in Du Puy et al. (2002), M. manomboensis G. Lefèvre & Labat and M. dupuyana M. Morales & Fortunato have been described (Lefèvre & Labat, 2006; Morales & Fortunato, 2016). Including the new species described here, 36 Mimosa species are currently known from the island, 34 of which are endemic or near-endemic.
Taxonomic treatment
Mimosa ibityensis E.J.M. Koenen, sp. nov. (Fig. 1, 2).
Holotypus: Madagascar. Reg. Amoron'i Mania [Prov. Fianarantsoa]: massif d'Ibity, col des Tapias along RN7 between Antsirabe and Ambositra, 20°14′11″S 47°05′56″E, 1450 m, 8.I.2014, fl., fr., Koenen, Andrianirina & Aebli 188 (TAN!; iso-: G!, K!, MO!, P!, WAG!, Z!).
Mimosa ibityensis E.J.M. Koenen is morphologically similar to M. vilersii Drake, but differs in having smaller leaflets up to 4 × 1 mm (up to 12 × 2.5 mm in M. vilersii) and unarmed replum (with prickles in M. vilersii).
Shrubs, scrambling, up to 1 m high. Twigs grooved, puberulous, with some red glandular hairs in the grooves when young, covered with many scattered, caducous prickles. Stipules linear, 2–3 mm long, persistent. Leaves bipinnate, up to 7 × 4 cm, with a delicate feather-like appearance, rachis 0–5 cm long, both grooved above and on the sides, pubescent and sometimes with prickles beneath, pinna apex shortly mucronate; petiole 1–1.5(–2) cm long. Pinnae in (1–)3–9 pairs per leaf, axes (0.5–)1–2 cm long, ridged above, pubescent and with red glandular hairs near the leaflet bases, paraphyllidia present. Leaflets (6–)10–25 pairs per pinna, c. 3–4 × 1 mm, sessile, narrowly oblong, base oblique, broadly rounded on the proximal side, cuneate on the distal side, apex rounded, midrib displaced towards the distal margin with usually only a single visible secondary vein arising from the leaflet base on the proximal side, sometimes a faintly visible additional secondary vein on the proximal side and/or also one on the distal side, glabrous except for the ciliate leaflet margins. Inflorescences in axillary capitula of c. 25 flowers, solitary or in pairs, peduncle 2–3.5 cm long, grooved, pubescent with red glandular hairs in the grooves, often with a pubescent linear bract up to 1 mm long located up to 1 cm below the capitulum. Flowers diplostemonous, 4-merous, sessile, subtended by a pubescent linear bracteole to 1 mm long. Calyx cup-shaped, up to 1 mm long, with an entire margin, with a few hairs near the base and a ciliate margin, pale brown. Corolla c. 3 mm long, tube 1.5–2 mm long, lobes with an acute apex, pale brown to slightly pinkish. Stamens 8, filaments c. 7 mm long, bright pink, anthers dorsifixed, white. Ovary 1.2–1.5 mm long, pubescent, on a 0.2–0.5 mm long stipe, style c. 7 mm long. Fruit (unripe) a craspedium, up to 4.5 × 1.2 cm, on a 6–7 mm long stipe, 2-seeded, constricted between the seeds, pubescent and covered with scattered red glandular hairs, replum lacking prickles. Seeds (mature) not seen.
Etymology. – The epithet ibityensis refers to the Massif d'Ibity as all known collections of the new species come from this mountain range and its vicinity.
Distribution, ecology and phenology. – Central Highlands of Madagascar. The new species is known only from the Massif d'Ibity and surrounding area. It was found in sclerophyllous Tapia forest on quartzite rock at elevations of 1450–1750 m (Fig. 1F). Specimens in flower have been recorded from October to January and in March, unripe fruits in January.
Notes. – The distinguishing features of this new species of Mimosa are: leaves with (1–)3–9 pairs of pinnae each with (6–)10–25 pairs of small leaflets, and especially the absence of prickles on the replum (the persistent margin) of the fruits (Table 1). Mimosa vilersii has also been reported from Tapia forest vegetation, but differs in having larger, more widely spaced leaflets and a prickly replum. Mimosa andringitrensis R. Vig., endemic to the Andringitra Massif and occurring in ericoid lichen forest and scrubland up to 2000 m, can be easily separated from the new species by the leaves with fewer pinnae (1–3) and fewer but larger pairs of leaflets per pinna (4–8), and the prickles on the replum (DU PUY et al., 2002). Mimosa dumetaria has similar foliage but has prickles on the replum (DU PUY et al., 2002); it is known only from the type locality in dry spiny scrub close to sea level near Toliara. Mimosa menabeensis is similar in having fruits lacking prickles on the replum but these are larger and not constricted between the seeds; in addition, it generally has larger leaves with more pinnae pairs and leaflet pairs per pinna. It thrives at lower elevations in N, W, and S Madagascar and is absent from the Central Highlands (DU PUY et al., 2002).
Additional specimens examined. – Madagascar. Reg. Amoron'i Mania (Prov. Fianarantsoa): col des Tapias, ad septentrionem Ambositra (Ilaka) in fruticetis montanis pauperrimis, fl., 19.XI.1967, Bernardi 11585 (P [P00465257]!); 45 km avant Ambositra, col des Tapias, I.1964, fl., Bosser 18800 (P [P00465261, P00465262]!); Ambositra, 10.X.1939, fl., Decary 15101 (P [P00465263, P00465264]!); ibid., 10.X.1906, fl., d'Alleizette s.n. (P [P00464400]!). Reg. Vakinankaratra (Prov. Antananarivo): massif d'Ibity, forêt sclérophylle de Tapia sur quartzite, à 2 km sud du village d'Ibity, 20°04′43″S 47°00′44″E, 1738 m, 21.X.2004, fl., Lehavana et al. 149 (MO, P [P00735992]!, TAN); pente de l'Ibity au S d'Antsirabe, [20°07′S 47°01′E], III.1914, fl., Perrier de la Bâthie 4232 (P [P00581877]!). Sine loco: s.d., Anon. 1444 (P [P00464401, P00464402]!).
Fig. 1.
Mimosa ibityensis E.J.M. Koenen. A. Inflorescence and foliage; B. Close-up of inflorescence; C. Immature fruit; D. Leaf; E. Habit; F. Habitat: Tapia forest at the type locality, with the characteristic tree species Uapaca bojeri Baill. [Koenen et al. 188] [Photos: E. Koenen]
Fig. 2.
Mimosa ibityensis E.J.M. Koenen. A. Leaf rachis apex; B. Individual flower; C. Flower opened out to show pistil and stamens; D. Bracteole; E. Pinna pulvinule with paraphyllidia below the first pair of leaflets; F. Adaxial view of leaflet; G. Abaxial view of leaflet; H. Flowering branch; I. Base of petiole with stipules and prickles on the main stem; J. Fruiting branch. [Koenen et al. 188, K] [Drawing: R. Wise]
Table 1.
Comparision of morphology, habitat, and distribution between Mimosa ibityensis E.J.M. Koenen and similar species based on Du Puy et al. (2002) and own observations.
Addition to the key to the species of Mimosa in Madagascar
[to be introduced at couplet 27 of key by DU PUY et al. (2002)]
Fruit with prickles or protuberances on replum M. vilersii
Fruit lacking prickles or protuberances on replum 28
Leaves with (1–)3–9 pairs of pinnae, (6–)10–25 pairs of leaflets per pinna; fruit up to 4.5 cm long, constricted between seeds; Central Highlands in Tapia forest between 1450–1750 m M. ibityensis
Leaves with (2–)9–35 pairs of pinnae, 13–50 pairs of leaflets per pinna; fruit up to 8.5 cm long, not constricted between seeds; N, W, and S Madagascar in deciduous woodland up to 700 m M. menabeensis
Acknowledgments
I thank my PhD supervisor Colin Hughes for tremendous support during this research project and for useful comments on an earlier version of the manuscript; Stuart Cable, Franck Rakotonasolo, and Hélène Ralimanana from the Kew Madagascar Conservation Centre for assistance in organizing the fieldwork, as well as Anahita Aebli and Herson Andrianirina for assistance in the field; the herbarium in Paris for access to their collections and in particular Myriam Gaudeul for acting as my Synthesys host during my visit to P; Rosemary Wise for preparing the beautiful drawing; and Gwilym Lewis and an anonymous reviewer for providing useful and insightful comments that have significantly improved the manuscript.This work was supported by a Swiss National Science Foundation grant to Dr. Colin Hughes (grant number 31003A_135522) and by the SYNTHESYS+ project ( http://www.synthesys.info).
Published by the Conservatoire et Jardin botaniques de Genève Open access article under Creative Commons Attribution Licence (CC BY 4.0)
