Mimosa terribilis Marchiori & Sobral ex Schmidt-Silveira & Miotto, 2016

Silveira, Fernanda Schmidt, Bordignon, Sérgio A. L. & Sfoggia Miotto, Silvia T., 2016, A New Endemic Mimosa (Leguminosae, Mimosoideae) from Pampa Biome, Brazil, Phytotaxa 245 (3), pp. 197-206 : 198-200

Mimosa terribilis Marchiori & Sobral ex Schmidt-Silveira & Miotto sp. nov.

Type:— BRAZIL. Rio Grande do Sul: Pelotas, Cascata , BR-392, ca. 32.4 km do trevo com a BR-116, 29 August 1998, J. A. Jarenkow 3849 (Holotype ICN!; isotypes K! MBM! NY!) .

( Fig.1 , 2 , 3 , 4 & 5 )

Mimosa terribilis is a subshrub, which has puberulent indumentum covering branches and peduncles, recurved aculei, 1-jugate leaves, with longer petioles in relation to pinna length, inflorescence capituliform globose, calyx subcoriaceous without defined lobes, corolla puberulent at lobes, fruits craspediform and hispid. The new species resembles Mimosa ramosissima , but it differs by its non-hirsute indumentum, calyx that is neither lobate nor nervate, shorter peduncles (3–6mm long) and its distribution area is limited to south of Rio Grande do Sul state in Brazil ( Tab. 1).

Subshrubs virgately branching or humifuse to diffusely ascending, 0.5–2 m tall, leaves sensible to touch. Branches alternated, dark gray, with grooves, almost glabrous, except by thin, canescent, diminute trichomes (puberulent indumentum) and armed with recurved aculei. Aculei 2–3 mm long, with lateral expanded base, being at internodes with subopposed to alternate distribution. Leaves bipinnate, 1-jugate, pinna 3–19 mm long, 6–22 pairs of leaflets. Spicule 0.6–0.9 mm long. Paraphyllidia lanceolate, small, 0.3–0.6 × 0.11–0.24 mm, puberulent, 1-nervate. Petioles developed, 2–6 mm long, puberulent. Leaflets narrowly oblong, 2.5–5 × 0.5–1 mm, concolor, asymmetric base and apex obtuse to mucronate, one central vein not visible at dorsal face, but outstanding at ventral face, yellowish punctuations present, margin with short thin and superimposed trichomes. Stipules linear-lanceolate, 2.5 × 0.5 mm with 1–2 main veins. Synflorescence racemose. Inflorescence capituliform, globose, peduncles 3–6mm long, puberulent. Bracts ovate, 0.9 × 2.0 mm, dorsally puberulent, margin glabrous, before anthesis smaller than corolla. Calyx narrowly campanulate, subcoriaceous, glabrous, 0.75–1mm long, reddish-brown, margin with small thin trichomes, lobes neither defined nor nervate, covering fast half of corolla length. Corolla tubular, 2.0–2.5 × 0.5 mm, lobes covered with thin antrorse trichomes. Ovary oblong with a tuft of trichomes at apex. Stamens exserted 3–4.5 mm long; free, lilac-pink. Fruits a craspedium, 1–10 per capitulum, oblong-ondulate, 13–15 × 3–5 mm, stipitate, the stipe 0.6–1 mm long, 1–4 articulate, apex cuspidate, valves with stiff setae trichomes and replum glabrous or sometimes with some stiff setae. Seeds ovoid, brown, 2.4–2.7 × 1.6–2 mm, pleurogram present.

Flowering and fruiting: —Flowers of this species have been collected from July to September. However, flowering time can be extended to October according to field observations. Fruits have been collected during November, but probably began to undergo fructification early, during September and October.

Distribution and ecology: — Mimosa terribilis is known only from seven different localities of Rio Grande do Sul State in Pampa Biome: Aceguá, Canguçu, Chuvisca, Dom Feliciano, Pelotas, Piratini and Rio Grande ( Fig. 5 ), where it was found growing on grasslands outcrops (rock grasslands), in grass fields and shrublands (vassoural), and at forest edge and roadsides, at approximately 100–300 m elevation. Almost all of these localities belong to Serra do Sudeste, in which we observed a mosaic of rock grasslands with a seasonal forest vegetation. This region has undulate relief and altitude between 150 and 500 m, being the oldest geological area of this state ( Boldrini 1997). Furthermore, the Serra do Sudeste region is distinguished as a high-level priority area for conservation (CNCFlora 2014). At a higher scale, this region belongs to Pampa Biome, which is considered one of the main hotspots of the global biodiversity; it is one of the Priority Areas for the Flora and Fauna Conservation (MMA 2000, 2007).

This species shares the same habitat with other Mimosa species from section Mimosa occurring on RS State as M. ramulosa Bentham (1841:385) and M. dutrae Malme (1931:10) . On open grassland and shrubland, it is easy to find M. terribilis occurring together with M. ramulosa . On forest edges near roadsides, this plant creates a wall of up to 2 m height, densely stiff and consequently harmful, which is trimmed near roadsides.

Taxonomic position: — Mimosa terribilis seems to belong to subser. Ramosissimae of Barneby (1991), owing to its similarity to M. ramosissima . According to Barneby’s description (1991) subser. Ramosissimae has many plastic characters as following: capitula format (globose or ellipsoid), stipule number of veins (1 or 4–6), calyx length (minute or bigger) and petioles length (subsessile or developed). Nevertheless, it subseries can be recognized by the habit, aculei format and geographical distribution. Thus, subser. Ramosissimae are usually shrubs or subshrubs armed with recurve or subrecurved aculei from South Brazil. This subseries has been represented by four species restricted to the south and southeast of Brazil. These are M.ramosissima ; M. oblonga var. oblonga (1841:365), M. oblonga var. pinetorum Barneby (1991:600–601) and M.orthacantha Bentham (1841:365–366) . In recent phylogenetic studies, species of subser. Ramosissimae are part of a large unresolved clade, which is called clade X, with members of many other subseries such as Sparsae, Dryandroideae and Obstrigosae, besides members of Calothamnos Barneby section, suggesting that this subseries as many others are not monophyletic ( Simon et al. 2011).

Etymology: —The specific epithet refers to the number of aculei throughout the plant that make it untouchable.

Conservation Status: —Although we observed large populations during field work, most of these were near roadsides, where they are removed due to the expansion of highways or by road maintenance. This fact probably increases the vulnerability of M. terribilis ; however, for assignment of its conservation status, sufficient data are still lacking. At the present time, we do not know if these populations around roadsides can survive into the future. The ecology, dispersal and reproductive system of this species are not known. Therefore, we have chosen to assess the species in the category data deficient (DD), according to the IUCN red list criteria ( IUCN 2001).

Comments: —The specimen identified as Mimosa terribilis for Soledade City by Matías Morales deposited on MBM herbarium at the number 115724 (Sobral et al. 5250 collector) is not the reported species; however, it is Mimosa sparsa Bentham (1841:385–386) another endemic species of Rio Grande do Sul State. Furthermore, the three other collections identified as Mimosa terribilis on MBM Herbarium include this new species.

Additional Specimen Examined (paratypes)— BRAZIL, Rio Grande do Sul: Aceguá, Projeto de Assentamento Estância do Fundo , August 2006 (fl), M. Grings 1383 ( ICN!) ; Chuvisca , 7 November 2014 (fr), Schmidt-Silveira & S. Bordignon 824 ( ICN!, HUCS!, MBM!, NY!, PACA!) ; Canguçu , September 1998 (fl), M. Sobral & J. A. Jarenkow 8763 ( ICN!, NY!, MBM!, RB!) ; Dom Feliciano , 7 November 2014 (fr), Schmidt-Silveira & S. Bordignon 825 ( ICN!, HUCS!, MBM!, NY!, PACA!) ; Pelotas, Cascata , BR-392, 29 August 1998 (fl), J. A., Jarenkow, 3847 ( ICN!, MBM!, PEL!, NY!) ; Pelotas, na divisa com Canguçu , 20 November 1986 (fr), J. Mattos 29965 ( HAS!) ; Piratini , 11 November 1976 (fr), T. M. Pedersen 11459 ( MBM!) ; Rio Grande, Ilha Leonídeo , 17 August 1982 (fl) I. V. Gonçalves w.n ( HURG 000365 !) .

Figures

FIGURE 1. Mimosa terribilis as virgate subshrubs of Pampa Biome, Southern Brazil. Species growing: (a, b) along roadsides, (c, d) in grasslands. Details of Mimosa terribilis inflorescences (e).

FIGURE 2. Holotype image of Mimosa terribilis, which has only flowers, from Pelotas City, deposited in the ICN Herbarium. Isotypes are deposited in ICN, K, MBM and NY Herbaria.

FIGURE 3. Mimosa terribilis details: (a) capituliform inflorescence; (b) fruits with stiff setae on valves; (c) flowers on prefloration; (d) fruits with a short stipe; (e) corolla pubescent and calyx campanulate subcoriaceous with margin ciliolate.

FIGURE 4. Mimosa terribilis details: (a) aculeate branches; (b) detail of puberulent indumentum; (c) spicule and paraphyllidia; (d) leaflet, ventral face; and (e) leaflet, dorsal face.

FIGURE 5. Distribution of Mimosa terribilis (black) and Mimosa ramosissima (grey) in State of Rio Grande do Sul, South Brazil.