Mimosa sobralii Grings & O.S. Ribas, 2013

Grings, Martin & Ribas, Osmar Dos Santos, 2013, Mimosa sobralii (Fabaceae, Mimosoideae), a new tree species endemic to the southern Brazilian highland slopes, Phytotaxa 131 (1), pp. 23-28 : 23-26

Mimosa sobralii Grings & O.S. Ribas , sp. nov. ( Figures 1 , 2 and 3 ).

Species nova M. bifurcae proxima , a qua habitu arboreo et floribus flavis recedit.

TYPE:— BRAZIL. Rio Grande do Sul: Nova Petrópolis, Linha Imperial , near “CTG”, 19 August 2012 , M. Grings 1677 (holotype ICN!, isotypes MBM!, MO!, K!).

Shrub or small tree 3–8 m high. Branches unarmed, reddish-brown, sometimes transversely angulose with 5 more or less prominent ribs, glabrous or with sparse whitish trichomes 0.1–0.2 mm. Internodes 10–15 mm. Stipules orbicular or suborbicular and revolute, subglobose, 0.8–1mm, sometimes with whitish trichomes in the abaxial surface. Leaf-stalks (petiole and primary rachis) glabrous and canaliculate, 13–47 × 0.5–0.7 mm, with a spicule-like linear mucron 0.4–1.2 mm long, curved downward at the apex; pinnae 2–6 on each side, opposite or alternate along the leaf-stalk, 25–36 × 0.3 mm; paraphyllidia reniform, glabrous, 0.2–0.3 × 0.5 mm, distant 0.8–1 mm from the first leaflet; leaflets alternate, 5–20 at each side, the distance between them 1– 1.5 mm, elliptic or subquadrate, 1–5 × 0.7–3 mm, resinous, glabrous or with scattered trichomes like those in the branches, concolor or slightly discolor, the midvein faintly visible abaxially and dividing the leaflet asymmetrically, the abaxial surface densely covered with dark rounded resinous glands 0.1 mm in diameter, the margin slightly revolute and occasionally with whitish cilia 0.1 mm long; apex rounded, sometimes the midvein excurrent; base obliquely obtuse or subcordate. Inflorescences in globose capitula axillary or in terminal panicles, 30–40–flowered, 3–4 mm diameter without stamens, 2–8 heads per branch, 2 inserted at the same point and presenting 20–30 linear colleters 0.3 mm at the base of the peduncles, these 2–8 × 0.2–0.3 mm; floral bracts lanceolate-obovate, 0.4 × 0.2 mm; flowers as far as examined bisexual; calyx campanulate, 0.4–0.5 × 0.4 mm, glabrous, straw-colored, membranous, generally without evident lobes but sometimes with margin irregularly lacerate; corolla campanulate, glabrous, pale yellow, 4–lobed, 1.3–1.5 × 0.8–1 mm including the lobes; lobes triangular, 0.4–0.5 × 0.4 mm, markedly 1–nerved, with scattered papillae 0.1 mm in diameter at the apex; stamens seven or eight, bright yellow, four 2–2.5 mm and four 3–3.6 mm; anthers globose, 0.3–0.4 × 0.3 mm; style 3–3.5 mm; ovary fusiform, glabrous, verrucose, 0.6–0.7 × 0.3 mm, the scattered warts 0.05 mm in diameter. Fruit a craspedium, 10-43 × 3-3,5 mm, 1-6 articulate, glabrous, veined, with glands, constricted between seeds, shortly stipitate, apex acute, with 2–6 seeds, 3,5 × 2,5 mm, elliptic, brown to black.

Mimosa sobralii is closely related to Mimosa bifurca Bentham in Hooker (1842: 407), a variable and widespread species occurring mostly in grassland formations from Argentina, Paraguay, Uruguay and Brazil, in the latter from São Paulo as far south as Rio Grande do Sul State ( Barneby 1991). However, M. sobralii has a very restricted range (endemic species) and quite distinct habitat and flower color. This new species is an exception within sect. Batocaulon , which Barneby (1991) described as never having yellow perianth parts. The following key summarizes the distinguishing characters between both species.

Figures

FIGURE 1. A. Branches with flowers (in most leaves of this material many pinnae fell, which is common in a lot of individuals of this species). B. Detail of stem hair-covering, sometimes with sparse whitish tichomes. C. Globose capitulum (some stamens fell). D. Flower and floral bract. E. Floral bract. F. Stamens, two sizes. G.Ovary and style. H. Adaxial surface of leaflet. I. Abaxial surface of leaflet densely covered with dark rounded resinous glands (Illustrator: Diana Carneiro).

FIGURE 2. A. Flowering branches. B, C. Rhytidome. D, E. Leaves and reddish-brown stems. F, I. Leaf-stalks canaliculate, paraphyllidia reniform. G. Branch with immature fruits. H. Habit. J, K. Mature fruits: craspedia and seeds (J=scale 1mm, K=scale 1cm)(K. photo: Valdely Kinupp). L. Abaxial surface of leaflets densely covered with dark rounded resinous glands.

FIGURE 3. Distribution of Mimosa sobralii and Mimosa bifurca in South America.