Solanum rhizomatum Saerkinen & M.Nee, 2015

Saerkinen, Tiina, Knapp, Sandra & Nee, Michael, 2015, Two new non-spiny Solanum species from the Bolivian Andes (Morelloid Clade), PhytoKeys 47, pp. 97-109 : 99-104

Solanum rhizomatum Saerkinen & M.Nee sp. nov. Figs 3 , 4

Diagnosis.

Like Solanum pygmaeum Cav., but differing in having mostly 1-branched inflorescences with 6-15 flowers, anthers <3.5 mm long, strongly recurving fruiting pedicels, and berries <1 cm in diameter with fewer than 30 seeds.

Type.

Bolivia. Santa Cruz: Prov. Vallegrande, 10 km (by air) NNW of Vallegrande, 18°23'S, 64°08'W, 1850 m, 1 Feb 1987, M. Nee & G. Coimbra S. 33947 (holotype: LPB; isotypes: G, MO [MO-5894880], NY [NY00824501]).

Description.

Rhizomatous herb with erect stems up to 15-50 cm tall arising from an underground rhizome. Stems 1.5-4.0 mm in diameter at base, slightly flexuose, terete to ridged, often slightly winged, often purple-coloured, glabrous to sparsely pubescent with appressed 1-4-celled simple uniseriate trichomes ca. 0.5 mm long. Sympodial units difoliate, not geminate. Leaves simple, 2.3-8.0 cm long, 1.2-4.3 cm wide, ovate-lanceolate; adaxial surface glabrous or sparsely pubescent with 1-2-celled spreading hairs along lamina and veins; abaxial surface pubescent only along veins; primary veins 4-6 pairs; base attenuate to decurrent; margins lobed to entire, often purple-tinged, pubescent with short, 1-celled simple uniseriate trichomes, if present lobes present throughout or most commonly only in the basal 1/3 of the blade; apex acute to acuminate; petiole 0.5-1.2 cm long, sparsely pubescent with spreading, simple uniseriate trichomes like those of the stems and leaves. Inflorescences 1.5-3.1 cm long, lateral and internodal, simple to 1-branched, with 6-15 flowers, sparsely pubescent with simple 1-4-celled uniseriate appressed trichomes; peduncle 1.0-2.4 cm long, and if branched, each branch with a rachis 3-4 mm long; pedicels 4-6 mm long, ca. 0.3 mm in diameter at the base and ca. 0.4 mm in diameter at the apex, straight and spreading at anthesis, articulated at the base; pedicel scars spaced 1-2 mm apart. Buds ovoid, white or purple-tinged. Flowers 5-merous, all perfect; calyx tube ca. 2.0-2.5 mm long, the lobes 1.0-1.5 mm long, triangular with acute apices, sparsely pubescent with simple 1-3-celled appressed uniseriate trichomes; corolla 1.2-1.5 cm in diameter, white or flushed with blue, with a yellow-green basal star, stellate, lobed 1/2 to 2/3 of the way to the base, the lobes 4.0-5.0 mm long, 2.5-3.0 mm wide, reflexed at anthesis, later spreading, densely pubescent abaxially with 1-2-celled simple uniseriate trichomes, these usually shorter than the trichomes of stems and leaves, glabrous adaxially; filament tube 1.2-1.5 mm long; free portion of the filaments 1.0-1.2 mm long, pubescent along internal side with spreading hairs like those of the stems and leaves; anthers 3.2-3.5 mm long, 0.9-1.0 mm wide, ellipsoid or rectangular in outline, yellow; ovary globose, glabrous; style 6-7 mm long, exerted 2.5-3.0 mm beyond the anther cone, densely pubescent with 4-celled simple uniseriate trichomes in the basal 2/3; stigma globose, minutely papillate. Fruit a globose berry, 6-7 mm in diameter, pale green (mature?), with a few stone cell aggregates; fruiting pedicels 1.2-1.4 mm long, ca. 0.6 mm in diameter at the base, ca. 0.8 mm in diameter at the apex, strongly recurving; fruiting calyx lobes 2.5-3.5 mm long, appressed to the berry with the tips slightly reflexed. Seeds 15-25 per berry, 1.7-1.8 mm long, 1.4-1.5 mm wide, concave-reniform, pale brown, the hilum positioned towards the narrower end of the seed, the testal cells pentagonal in outline.

Distribution.

Endemic to the arid interior valleys of the Bolivian Andes in the Departments of Cochabamba, Potosí, Santa Cruz, and probably Chuquisaca, growing in seasonally dry tropical forests and dry matorral vegetation, along slopes and on rocky and sandy soils, often found growing in moist depressions under the shade of larger trees and thickets, associated with Prosopis kuntzei Harms ex Kuntze, Jodina rhombifolia (Hook. & Arn.) Reissek, legumes, grasses, columnar cacti, and Asteraceae herbs; between 1,300 and 2,900 m elevation.

Ecology.

Flowering and fruiting during the wet season from Jan. to March.

Etymology.

Solanum rhizomatum is named for its rhizomatous underground stem.

Conservation status.

We assign a preliminary IUCN threat status of Least Concern (LC) to Solanum rhizomatum based on the known extent of the species occurrence (EOO=43,101 km2). The extremely small observed area of occupancy (AOO=48 km2) could merit endangered status (EN), but knowing that collection densities in the tropical Andes remain extremely low and considering that current collections are from>10 different localities, we prefer basing our threat status assessment on the extent rather than area of occurrence. It is not known whether Solanum rhizomatum is similar in its biology and vegetative spread to Solanum pygmaeum , and further studies may clarify this aspect of potential conservation assessments in the future. No populations are known thus far from the protected area network in Bolivia. The growth form that allows effective vegetative spreading would indicate that the species can withstand grazing pressures moderately well.

Specimens examined.

Bolivia. Cochabamba: Prov. Campero: Mizque, 2,020 m, 20 Feb 1967, R.F. Steinbach 721 (US); ca. 5 km de Villa Granada hacia Peña Colorada, 18°12'10"S, 65°00'09"W, 2,201 m, 25 Feb 2004, J.R.I. Wood 20266 (K, LPB). Prov. Cercado: en la salida de Cochabamba hacia el Valle Alto pasando La Tranca y ca. 2 km antes de la Angostura, 17°30'24"S 66°05'35"W, 2,676 m, 10 Feb 2005, J.R.I. Wood 21590 (K). Potosí: Prov. Nor Chichas: 4 km N of Cotagaita on road to Potosí, 20°50'S, 65°41'W, 2,900 m, 30 Mar 1997, J.R.I. Wood 11974 (K, LPB). Santa Cruz: Prov. Caballero: carretera de Pulquina a Saipina a 0.5 km al oeste de la cumbre, 18°05'58"S, 64°30'56"W, 1,788 m, 20 Feb 2003, J.R.I. Wood 19134 (BOLV, K). Prov. Florida: 3 km S of Mataral, 18°08'S, 64°13'W, 1,425 m, 6 Feb 1988, M. Nee 36252 (MO, NY, USZ); 4 km by road W of Mataral, 18°09'21"S, 64°15'17"W, 1,300 m, 22 Feb 1984, G. Schmitt 27A (MO). Prov. Vallegrande: Pueblo de Vallegrande, Cerro los Tres Pilares, 100-150 m antes de llegar a la cima sobre el sendero hacia el pueblo, 18°29'21"S, 64°07'13"W, 2,236 m, 19 Jan 2003, M. Mendoza 449 (K); Choroquetal, ca. 5 km de Vallegrande sobre la carretera a Mataral, entrando ca. 500 m, sobre la senda hacia Chacateal, 18°28'07"S, 64°07'25"W, 1,932 m, 17 Mar 2003, M. Mendoza 529 (K); 4 km SW El Trigal, 18°20'S, 64°10'W, 1,600 m, 8 Mar 1988, M. Nee 36536 (MO, NY, USZ); Las Cañas, 2500 m, 28 Feb 1984, C.M. Ochoa 15548 (US); 6.5 km (by air) NE of airport in Vallegrande, along bad dirt road down into the Río San Blas valley, 18°26'33"S 64°03'12"W 1,795 m, 3 Jan 2011, M. Nee & M. Mendoza 57594 (USZ).

Discussion.

Solanum rhizomatum is most closely related to Solanum pygmaeum from central and coastal Argentina (see Barboza et al. 2013), another rhizomatous species of Solanum section Solanum . Solanum rhizomatum differs from Solanum pygmaeum in having mostly 1-branched inflorescences with 6-15 flowers, anthers 3.2-3.5 mm long, strongly recurving fruiting pedicels, and berries with 15-25 seeds, while Solanum pygmaeum always has simple (unbranched) inflorescences with 2-6 flowers, anthers usually>3.5 mm long, fruiting pedicels that are broadly spreading, and berries with>50 seeds. Although these sets of characters overlap to some extent, Solanum pygmaeum individuals are generally smaller than those of Solanum rhizomatum (10-20 cm tall), with smaller leaves 1-5 cm long and 0.5-2.2 cm wide, while Solanum rhizomatum grows 15-50 cm tall, with larger leaves 2.3-8.0 cm long and 1.2-4.3 cm wide. Solanum pygmaeum forms dense colonies in secondary habitats such as railroad sidings, and has been introduced and naturalised in Europe and North America, presumably in boats carrying wool from eastern coastal Argentina ( Barboza et al. 2013).

As in many species of Solanum , variation in corolla colour occurs in Solanum rhizomatum , where corollas vary from white to pale lilac even within single individuals. Label information from Nee & Mendoza 57594 notes changes in the corolla colour during development, where the corolla is white in bud, violet in anthesis, and darker after wilting.

Figures

Figure 3. Paratype of Solanum rhizomatum (Wood 11974, K).

Figure 4. Solanum rhizomatum. A Habitat in seasonally dry forests, eastern Bolivian Andes, Vallegrande, Dept. Santa Cruz B Habit amongst low herbs in partial shade C Rhizome D Inflorescence (A-D Nee & Mendoza 57594). Photos by M. Nee, scale bars = 1 cm.