Calibrachoa longistyla Stehmann & Greppi 2011, sp. nov.

Calibrachoa longistyla Stehmann & Greppi, sp. nov. (Fig. 2 A–H, 3 D–E)

Calibrachoa sui generis, sed stigmate satis superanti ab antheris staminum majorum bene differt.

Type:— ARGENTINA. Corrientes: Santo Tomé, camino a Azara, 29 o 39.73’ S, 56 oO 9˙93 W ̕ September 2OO3̕ J . Greppi & T. Kamogawa 1007 (holotype BAB).

Shrub to 0.3 m tall, decumbent with ascending secondary branches; stems cylindrical, woody at base, grayish brown, irregularly striate, sparsely pubescent, ochraceous, pubescent with simple uniseriate 3–7(–9)-celled glandular trichomes 0.1–0.4 mm long; internodes 2–8 mm long; brachyblasts lacking or small, up to 3.2–4.0 mm long. Leaves sessile or subsessile, the blades 8–15 × 6–8 mm, elliptic, the apex acute, the base obtuse or rounded, the margin slightly thickened, ciliate, symmetrical, plane, pubescent on both sides, the midrib sunken adaxially and prominent abaxially, lacking a ligneous callus at the base. Inflorescence of sympodial units, each composed of a single flower associated with 2 opposite leaf-like bracts; pedicels 3.0– 9.5 mm long, pubescent; calyx 8–13 mm long, olive-green to yellowish-brown, puberulent externally and internally, 10- nerved, the nerves thickened, cleft to below the middle, the lobes 4–8 mm long, unequal, linear-lanceolate, the apex acute; corolla narrow-funnelform, the tube 14–18 mm long, cylindrical at the base, 8–10 mm long, increasing in diameter toward the apex, externally yellow with marked purple venation, internally yellow, minutely pubescent outside, glabrous inside, the limb white, ca. 15 mm diam., shallowly to halfway lobed, the lobes with purple midrib, 5–6 mm long, obtuse or truncated, the apex abruptly short-acute; stamens 5, included, with 3 distinct lengths; filaments with the free portion 3 mm, 3.5 mm, and 5 mm long, the adnate portion about 3 mm long, glabrous; anthers yellow, ca. 0.8 mm long, not connivent; nectariferous disk 2- lobed; ovary ovoid; style ca. 9–10 mm long, the apex curved; stigma dilated, slightly exserted above anthers of the longest stamens. Capsule 7 mm long, 4–5 mm diam., ellipsoidal; fruiting pedicels 9–16 mm long, deflexed; seeds 1.1–1.3 mm long, ellipsoidal to reniform.

Etymology:— The specific epithet refers to the style length, longer than the stamens, an uncommon character in the genus.

Distribution:— Few collections are known from near the Department of Santo Tomé, Corrientes, Argentina, inhabiting humid grasslands.

Calibrachoa longistyla is easily recognized by its white flowers with a curved style apex and stigma exserted above anthers of the longest stamens. All other species with longer styles, such as C. caesia, C. irgangiana, and C. sendtneriana (R.E.Fr.) Stehmann & Semir (1997: 419), have purple, pink or orange-red corollas.

Following the IUCN classification, C. longistyla should be included in the Criticallly Endangered (CR) category, because it is known only from a single locality that is not included in a protected area. The criteria applied were the geographic range with extent of occurrence <100 km, and area of occupancy restricted to one locality, with a continuing decline of quality of habitat (B1, B2a, biii).

Additional specimens examined (paratypes): — ARGENTINA. Corrientes: Santo Tomé, Ruta 14, 14 Km NE de Santo Tomé, Cuay Chico, banãdos, 3 September 2004, A . Schinini & M. Demateis 36548 (CTES 402577); localidad Santo Tomé, 28º33.81´S, 56º 03´W, 94 m, 12 October 2009, J . Greppi 1070 (BAB); localidad Santo Tomé, acceso a Santo Tomé, Ruta Nac. 14 y las vias del ferrocarril, al costado de las vias, 28º 33´S, 56º 04´W, 83 m, 12 October 2009, J . Greppi 1071 (BAB).