Solanum rhizomatum Saerkinen & M.Nee, PhytoKeys 47: 102. 2015.

Knapp, Sandra, Saerkinen, Tiina & Barboza, Gloria E., 2023, A revision of the South American species of the Morelloid clade (Solanum L., Solanaceae), PhytoKeys 231, pp. 1-342 : 1

47. Solanum rhizomatum Saerkinen & M.Nee, PhytoKeys 47: 102. 2015.

Figs 143 , 144

Type.

Bolivia. Santa Cruz: Prov. Vallegrande , 10 km (by air) NNW of Vallegrande, 18°23'S, 64°08'W, 1,850 m, 1 Feb 1987, M. Nee 33947 (holotype: LPB; isotypes: CORD [CORD00082080], G, MO [MO-5894880, acc. # 5894880], NY [00824501], US [02836499, acc. # 3146806] and to be distributed).

Description.

Perennial rhizomatous herbs with erect stems to 0.15-0.2 m high rising from an underground rhizome. Stems 1.5-2 mm in diameter at base, slightly flexuous, 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 or shallowly toothed or lobed, the blades 2.3-8 cm long, 1.2-4.3 cm wide, ovate-lanceolate, widest in the lower third, membranous, concolorous; adaxial surface glabrous or sparsely pubescent with 1-2-celled spreading hairs along lamina and veins; abaxial surface pubescent only along veins; principal veins 4-6 pairs; base attenuate to decurrent; margins shallowly toothed to entire, often purple-tinged, pubescent with short, 1-celled simple uniseriate trichomes, teeth, if present, 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 internodal, forked or several times branched (rarely unbranched), 1.5-3.1 cm long, with 6-15 flowers, sparsely pubescent with simple 1-4-celled uniseriate appressed trichomes; peduncle 1-2.4 cm long and if the inflorescence branched, each branch with a flower-bearing axis 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, cosexual (hermaphroditic). Calyx tube ca. 2-2.5 mm long, the lobes 1-1.5 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 blue, with a yellow-green basal star, stellate, lobed halfway to 2/3 of the way to the base, the lobes 4-5 mm long, 2.5-3 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. Stamens equal; filament tube 1.2-1.5 mm long; free portion of the filaments 1-1.2 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 mm wide, ellipsoid or rectangular in outline, yellow. Ovary globose, glabrous; style 6-7 mm long, straight, long-exserted 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, 0.6-0.7 cm in diameter, pale green (mature?), the pericarp thin, matte, glabrous; fruiting pedicels 1.2-1.4 cm long, ca. 0.6 mm in diameter at the base, ca. 0.8 mm in diameter at the apex, strongly deflexed, not persistent; 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, tear-drop shaped, pale brown, the hilum positioned towards the narrower end of the seed, the testal cells pentagonal in outline. Stone cells 4-7 per berry, ca. 0.5 mm in diameter, pale tan or creamy white. Chromosome number not known.

Distribution

(Fig. 145 ). Solanum rhizomatum is endemic to the arid interior valleys of the Bolivian Andes (Depts. Cochabamba, Potosí, Santa Cruz and also expected to occur in Chuquisaca).

Ecology and habitat.

Solanum rhizomatum grows in seasonally dry tropical forests and dry matorral vegetation, along slopes and on rocky and sandy soils, found often growing in moist depressions under the shade of larger trees and thickets; between 1,300 and 2,900 m elevation.

Common names and uses.

None recorded.

Preliminary conservation status.

Least Concern [LC]. EOO = 71,565 km2 [LC]; AOO = 80 km2 [EN]. Knowing that collection densities in the tropical Andes remain extremely low and considering that current collections of S. rhizomatum are from>10 different localities, we suggest this species is not of particular conservation concern. It is not known whether S. rhizomatum is similar in its biology and vegetative spread to S. pygmaeum and further studies may clarify this aspect for potential conservation assessments in the future. No populations are known thus far from the protected area network in Bolivia. The rhizomatous growth form that allows effective vegetative spreading would indicate that the species can withstand grazing pressures moderately well.

Discussion.

Solanum rhizomatum is most similar to S. pygmaeum from central and littoral Argentina (see Barboza et al. 2013; Särkinen et al. 2015d) and differs from S. pygmaeum in having mostly forked (or sometimes more highly branched) inflorescences with 6-15 flowers, anthers 3.2-3.5 mm long, strongly recurving pedicels in fruit, and berries with 15-25 seeds, while S. pygmaeum always has simple inflorescences with 2-6 flowers, anthers usually>3.5 mm long, pedicels that are broadly spreading in fruit and berries with> 50 seeds. Although these sets of characters to some extent overlap, S. pygmaeum individuals are generally smaller than those of S. rhizomatum (10-20 cm high), with smaller leaves 1-5 cm long and 0.5-2.2 cm wide, while S. rhizomatum grows 15-50 cm high, with larger leaves 2.3-8 cm long and 1.2-4.3 cm wide.

Like many species of Solanum , colour variation of the corolla based on herbarium labels is observed in S. rhizomatum where the corolla varies from white to pale lilac, even within individuals. Nee & Mendoza 57954 note changes in the corolla colour during development, where the c orolla is white in bud, violet in anthesis (Fig. 144D ), but darker after wilting.

Figures

Figure 143. Solanum rhizomatum A habit B inflorescence C infructescence with maturing fruits (A, B Wood 17690 [K 000658383]; C Wood 11974 [K 000658384]). Reproduced with permission of the Trustees of the Royal Botanic Gardens, Kew.

Figure 144. Solanum rhizomatum A habitat of seasonally dry forests B rhizome C, D inflorescence with flowers at anthesis (A-D Nee & Mendoza 57594). Photos by M. Nee. Previously published in Saerkinen et al. (2015 d: 105).

Figure 145. Distribution map of Solanum rhizomatum.