Mimosa osmarii L. Jordão, M.P. Morim, Baumgratz and Marc.F. Simon, 2017

Jordão, Lucas Sá Barreto, Morim, Marli Pires, Baumgratz, José Fernando A. & Simon, Marcelo Fragomeni, 2017, A new species of Mimosa (Leguminosae) endemic to the Brazilian Cerrado, Phytotaxa 312 (2), pp. 237-246 : 239-243

Mimosa osmarii L. Jordão, M.P. Morim, Baumgratz and Marc.F. Simon , sp. nov. ( Figs. 1–4 )

Mimosa osmarii is closely similar to M. paucifolia Benth. , but differs by the climbing prickly habit with stems reaching ca. 2.5 m long (vs. grass-like tufted with ascending stems reaching ca. 0.5 m tall), the stems, petiole, leaf rachis and raquilla serially armed on the ribs (vs. unarmed), petiole with same length of the leaf rachis or 2.8x longer (vs. (2.8–)3–11x longer), and the persistence of leaflets+rachilla (vs. caducous, with persistence of the petiole+rachis).

Type: — BRAZIL. Minas Gerais: Buenópolis. Parque Estadual da Serra do Cabral, Região do Cuba, Lapa da Dança, 17º55’31”S 44º14’24.5”W, 1077 m, 26 November 2015, fl., L.S.B. Jordão et al. 278 (holotype RB, isotypes CEN, NY).

Climbing prickly herb to subshrub, sciophilous or semi-sciophilous, perennial, xylopodium absent. Indumentum essentially glabrous, except for sparse trichomes subsessile-glandular, and rare trichomes filiform on margin of stipules. Stems reaching ca. 2.5 m long, slender and much-branched, pentagonal, grooved, ribbed, densely armed with decurved prickles <2 mm long along the ribs, also present ventrally on the petiole, leaf rachis and raquilla. Stipules 0.8–2 mm long, lanceolate, uninerved, persistent, ciliate or not. Leaf (1–)2–4 pairs of pinna (rarely leaves with 1 pair); petiole 13–35 mm long, 4-ribbed, same length of the leaf rachis or 2.8x longer; leaf rachis 5–35 mm long; spicule absent or rarely deltate, 1–1.5 mm long; paraphyllidia 0.2–3 mm long, lanceolate or linear, developing 1–5.5 mm from the pinna-pulvinus and 1.1–3 mm from the first pair of leaflets, but always closer to the first pair than the pinna-pulvinus; raquilla 0.35–2.5 mm long; leaflets 2–3 pairs on each pinna, 2–7.5 × 1.3–4.1 mm, obovate, base oblique-acute, oblique-rounded or obliquesubcordate, apex mucronulate-obtuse or mucronulate-rounded, margin non-ciliate, both faces glabrous, 1–2-nerved; persistence of the leaflets+rachilla. Inflorescence 2.5–6 mm diam., racemose, globose-capitate, 1–3-axillary, moriform (floral buds larger than bracteoles), peduncle 18–40 mm long; bracteole 0.4–0.9 mm long, lanceolate, glabrous. Flowers 4(–5)-merous, glabrous; calyx 0.4–0.6 mm long, campanulate, shortly denticulate; corolla 2–2.5 mm long, campanulate or turbinate; filaments 6–6.5 mm long, pinkish, fused at base 0.2–0.5 mm long; ovary glabrous. Craspedium 34–38 × 3.3–3.5 mm, 6–9-articulated, oblong, slightly curved; stipe 3–5 mm long; replum undulate, unarmed; epicarp unarmed, apparently glabrous, except for sparse subsessile-glandular trichomes. Seeds not seen.

Additional specimens examined (paratypes): — BRAZIL: Minas Gerais: Buenópolis. Serra do Cabral, Região do Cuba, Lapa da Dança , 17º55’29”S 44º14’23”W, 13 March 2007, fl. and fr., L. Pangaio et al. 903 ( RB) ; Parque Estadual da Serra do Cabral, Região do Cuba, Lapa da Dança , 17º55’31”S 44º14’24”W, 1077 m, 26 November 2015 ,

fl., L.S.B. Jordão et al. 276 ( RB, CEN) ; Lapa da Dança , fl., 26 November 2015, L.S.B. Jordão et al. 277 ( RB, CEN) ; Lapa dos Peixes, 17º55’29”S 44º14’31”W, 1019 m, 29 November 2015, fl., L.S.B. Jordão et al. 279 ( RB, CEN) .

Etymology: —Named in honor of Osmar dos Santos Ribas, a Mimosa specialist, important plant collector and former curator of the Museu Botânico Municipal (MBM), in Paraná State, for his contribution to the flora of southern Brazil.

Distribution and Habitat: — Mimosa osmarii is endemic to the Serra do Cabral, and known only from a small and restricted population of seven individuals adjacent to Parque Estadual da Serra do Cabral. This species is sciophilous or semi-sciophilous, and occurs in cerrado sensu stricto at 1,019 –1,077 m. No individuals were found in open areas or areas with high luminosity outside of cerrado sensu stricto.

Conservation status: — Mimosa osmarii is currently classified as Vulnerable (VU) due to the very small and restricted population (AOO= 4 km ²) and the frequency of fires within its native range, considering that the species is fire-sensitive. Serra do Cabral is a very threatened area owing to the high frequency of intentional and accidental fires. INPE (2016) reported 177 fires from July 2014 to June 2016 within Parque Estadual da Serra do Cabral. During fieldwork, we observed burned vegetation in the vicinity of the area where the individuals of M. osmarii were found, and the park rangers reported that fires are common in the region and difficult to control. As a plausible threat, this factor may cause the status of M. osmarii to become Critically Endangered (CR) or even Extinct (EX) in the near future if appropriate actions are not taken to manage the fires (R. Negrão, Lista Vermelha CNCFlora/JBRJ, at http://cncflora. jbrj.gov.br).

Comments: — Mimosa osmarii is distinguished from other species of Mimosa sect. Batocaulon ser. Paucifoliatae (sensu Barneby 1991) by the following set of characters: presence of decurved prickles in series on the stems, petioles, leaf rachis and rachilla, pentagonal stems, and leaves with (1–)2–4 pairs of pinna (rarely leaves with 1 pair), each one with 2–3 pairs of leaflets. Mimosa osmarii is easily identified among other armed species of M. ser. Paucifoliatae by its leaves with 2 to 3 pairs of leaflets (vs. more than 3 pairs), shorter raquilla (0.35–2.5 mm vs.> 3.5 mm), and craspedium with an undulate replum (vs. straight, except in varieties of M. gracilis Bentham (1842: 411) that have a slightly undulate replum; see the identification key of armed taxa of M. ser. Paucifoliatae below. Mimosa gracilis , which constitutes a taxonomic complex with seven varieties ( Barneby 1991), only occasionally bears prickles, but when present these are sparse and not in series along the ribs. A notable trait not very common in Mimosa , but found in M. osmarii , is the position of the paraphyllidia. In most species of Mimosa , the paraphyllidia are located immediately adjacent to the pinna pulvinus. In M. osmarii these develop distant from the pinna pulvinus, and closer to the first pair of leaflets or about the middle of the axis between the pulvinus and the first pair of leaflets.

Mimosa osmarii is also morphologically similar to the unarmed species M. paucifolia (M. sect. Batocaulon ser. Paucifoliatae ), sharing the following morphological features: slender stems, similar type and distribution of trichomes on the plant, leaf formula, and similar flower and craspedium. Nevertheless, Mimosa osmarii differs from M. paucifolia mainly because it is a sciophilous or semi-sciophilous plant (vs. heliophilous) with a climbing herbaceous to subshrubby habit whose stems can reach ca. 2.5 m long (vs. grass-like tufted herb with ascending stems reaching 0.5 m tall) and prickles serially arranged on the ribs of the stem, petiole, leaf rachis and raquilla (vs. unarmed plant) ( Tab. 1). The leaves of these taxa also have additional diagnostic features. Generally, the length of the petiole in M. osmarii (13–35 mm) is shorter than in M. paucifolia (15–100 mm), particularly when it is compared to the leaf rachis length, which measures 5–35 mm vs. 3.5–25 mm, respectively. Because of this overlap, we used the ratio between the length of petiole and leaf rachis to distinguish the two species ( Tab. 1). Another relevant feature related to the leaves that occurs only in M. paucifolia , and not in M. osmarii , is the fall of the leaflets+rachilla whereas the petiole+rachis remain attached to the plant ( Tab. 1), that gives to M. paucifolia its grass-like aspect.

Whereas Mimosa osmarii grows in the shade or partial shade in cerrado sensu stricto, both varieties of M. paucifolia are heliophilous plants occurs in campo limpo and campo sujo on sandy soils, and campos rupestres ( Fig. 3E–H , Tab. 1).

The typical variety of M. paucifolia occurs in the Triângulo Mineiro and west of Alto Parnaíba, and there is one record from the Central Brazilian Plateau, while M. paucifolia Bentham var. scoparia Barneby (1991: 224) has a wider distribution, occurring in Serra do Cabral, Morro do Gavião (in Parque Nacional das Sempre Vivas), Serra dos Três Irmãos, Serra da Canastra, and there is one record from the Central Brazilian Plateau ( Fig. 2 ). Although M. paucifolia var. scoparia has a sympatric distribution with M. osmarii in Serra do Cabral, they occur in different ecological niches.

Key to armed species of Mimosa sect. Batocaulon ser. Paucifoliatae

1. Stems trigonal............................................................................................................................................................... M. suburbana

- Stems pentagonal, or tetragonal.........................................................................................................................................................2

2. Leaves with only 1 pair of pinnae .................................................................................................................................. M. pinetorum

- Leaves with 2 or more pairs of pinnae (rarely leaves with 1 pair of pinnae in M. osmarii )..............................................................3

3. Humifuse, tufted, procumbent or decumbent herbs or subshrubs; stems with sparse prickles, not distributed in series... M. gracilis

- Climbing shrubs or subshrubs; stems densely armed, prickles in series along stem ribs..................................................................4

4. Leaves with rachilla 0.35–2.5 mm long, 2–3 pairs of leaflets............................................................................................ M. osmarii

- Leaves with rachilla 7 mm or longer, more than 6 pairs of leaflets...................................................................................................5

5. Leaves with (2–)3–12 pairs of pinnae, paraphyllidia unequal in length, the larger at least 2.5–3x longer than its pair; seeds with median pleurogram........................................................................................................................................................ M. diplotricha

- Leaves with (1–)2–4 pairs of pinnae, paraphyllidia equal in length or slightly unequal, the larger up to 1.3x longer than its pair; seeds with apical-basal pleurogram....................................................................................................................................................6

6. Leaves with rachilla 33–52 mm long, 15–26 pairs of pinnae................................................................................................. M. selloi

- Leaves with rachilla 7–27 mm long, 7–12 pairs of pinnae.............................................................................................. M. supravisa

Figures

FIGURE 1. Distribution of Mimosa osmarii and Mimosa paucifolia var. scoparia and incidence of fires in the Parque Estadual Serra do Cabral from July 2014 to June 2016. Data of fire obtained from INPE (2016).

FIGURE 2. Distribution of Mimosa osmarii, Mimosa paucifolia var. paucifolia and Mimosa paucifolia var. scoparia.

FIGURE 3. Mimosa osmarii: A–B. Habits; C–D. Details of the flowering branches. Mimosa paucifolia var. scoparia: E–F. Habits; G–H. Details of the flowering branches. Photographed by Lucas S.B. Jordão.

FIGURE 4. Mimosa osmarii: A. Flowering branch; B. Leaf; C. Flower; D. Bracteole; E. Detail of paraphyllidia; F. Transverse cross section of petiole; G. Detail of stem and stipule; H. Stipule; I. Transverse cross section of stem; J. craspedium. (A–I: L.S.B. Jordão et al. 278 RB; J: L. Pangaio et al. 903 RB). Illustrated by Maria Alice de Rezende.