Like Solanum sarrachoides Sendtn. and Solanum physalifolium Rusby but differing in having larger anthers 2.5–3.2 mm long, and similar to Solanum tweedianum Hook. in having long calyx lobes but differing in having a shorter calyx tube in both flower (0.8–1.3 mm) and fruit (2.0–2.5 mm).

Bolivia. Tarija: Prov. Gran Chaco, 44.5 km (by rd) W from upper bridge over Rio Pilcomayo and 17.7 NE of Palos Blancos, on rd from Villa Montes to Palos Blancos, 21°27'S, 63°40'45"W, 815 m, 21 Mar 2007 (fl,fr), M. Nee & R. Flores S. 54821 (holotype: LPB; isotypes: BM [BM001211859], MO [sheet number 6073914, barcode MO-2113149], NY [NY00853628], UT [UT-126715]; [records indicate that duplicates were sent to CAS, CORD, G, MEXU, NSW, SI, USZ, US, UT, WIS]).

Decumbent to erect subwoody herb to 1 m tall, spreading to up to 2 m in diameter. Stems 3–4 mm in diameter at base, spreading or erect, terete, straw coloured, glabrescent; new growth densely glandular-papillate and pubescent with a mixture of patent, simple, uniseriate eglandular and glandular trichomes, the trichomes of several lengths, 1-celled to 17-celled, 0.2–2 mm long, translucent, if glandular then with a terminal gland (this often breaking off). Sympodial units difoliate, not geminate. Leaves simple, (2.4–)4.0–7.6 cm long, (1.4–)2.3–3.0(–4.0) cm wide, ovate; adaxial surface moderately pubescent with both eglandular and glandular hairs along lamina and veins; abaxial surface more densely pubescent along veins; major veins 3–5 pairs; base truncate to rounded; margins entire to shallowly and unevenly lobed (mostly near the base); apex acute; petiole (0.7–)1.5–2.0 cm long, pubescent with spreading eglandular and glandular hairs like those on the stem. Inflorescences 2.5–3.5 cm long, lateral, internodal to leaf-opposed, simple, racemose, with (6–)7–10(–12) flowers, pubescent with both eglandular and glandular trichomes like those on stem; peduncle 1.4–3.3 cm long; pedicels spaced 0–1 mm apart, 6–10 mm long, ca. 0.2 mm in diameter at base and apex, straight and spreading at anthesis, articulated at the base. Buds ellipsoid, white or purple-tinged, densely pubescent with spreading, multicellular hairs (see under calyx), the corolla not strongly exerted from the calyx, exceeding the calyx lobes by less than ½ of their lenghts before anthesis. Flowers 5-merous, all perfect. Calyx tube 0.8–1.3 mm long, the lobes 1.4–3.7 mm long, 0.6–1.0 mm wide, triangular with long-acuminate apices, densely pubescent with both eglandular and glandular trichomes, the eglandular trichomes 1.5–3.5 mm long. Corolla 0.7–1.3 cm in diameter, white with a green-black basal central star, stellate, lobed 1/2 way to the base, the lobes 2.5–3.2 mm long, 1.5–2.5 mm wide, reflexed at anthesis, later spreading, sparsely pubescent abaxially with multicellular simple spreading eglandular uniseriate trichomes to 0.5 mm long, densely papillate on the tips and margins. Stamens equal; filament tube 0.1–0.25 mm long; free portion of the filaments 0.2–0.3 mm long, adaxially pubescent with tangled eglandular simple uniseriate trichomes; anthers 2.5–3.2 mm long, 0.9–1.1 mm wide, ellipsoid, yellow, poricidal at the tips, the pores lengthening to slits with age. Ovary subglobose, glabrous; style 4–5 mm long, exerted 1.5–2.0 mm beyond the anther cone, densely pubescent with 4-celled simple uniseriate trichomes in the basal ½ or 3/5 where included in the anther cone; stigma capitate, the surface minutely papillate. Fruit a subglobose berry, slightly flattened, 5–12 mm in diameter, green and mottled with white vein-like reticulations (black when ripe fide Fuentes & Navarro 2607), the surface of the pericarp shiny; fruiting pedicels 1.6–2.0 mm long, ca. 0.5 mm in diameter at the base, ca. 1.0 mm in diameter at the apex, spaced 1–2 mm apart, strongly recurving, dropping off with the fruit leaving raised pedicels scars to 0.1 mm high; fruiting calyx tube 2.0–2.5 mm long, the lobes 5–8 mm long and 3.0–3.5 mm wide, spreading to reflexed. Seeds 15–25 per berry, 1.7–2.0 mm long, 1.1–1.5 mm wide, tear-drop shaped, pale brown, the surface minutely pitted, the hilum positioned subapically, the testal cells pentagonal in outline. Stone cells absent.

(Figure 2). Endemic to Bolivia in the Departments of Tarija and Santa Cruz; although the species is to be expected in adjacent Paraguay. Solanum michaelis grows in dry Chaco vegetation and in lower inter-Andean valleys, along slopes in sandy soils in mostly unshaded dry creek beds on bare soil, often in areas that have been burned, or in more humid Chaco vegetation at the edge of “palmares” (stands of Copernicia alba Morong) between 300–900 m elevation.

Flowering in March and between June and September, fruiting from June to September probably toward the end of the rainy season (Jan-Apr) and then sporadically with occasional rains during the dry season.

The species epithet honours Dr Michael Nee, whose collections from Bolivia have provided the much needed material to complete descriptions of many recently published new species within Solanum, including the two described here. His collections and taxonomic work over the past 50 years have contributed to the understanding of morphological diversity of Solanum. His taxonomic work in the genus has been fundamental in resolving and typifying the 6,967 published names of Solanum.

The preliminary IUCN (IUCN 2014) threat status of Solanum michaelis is

Endangered

Bolivia. Santa Cruz: Prov. Cordillera, Parque Nacional Kaa-Iyá del Gran Chaco, hito 27 de noviembre, 20°05'16"S, 61°55'19"W, 320 m, 17 Jul 1998 (fl,fr), A. Fuentes 2607 (NY); alrededor del pueblo de la Brecha, 22 May 1999 (fl,fr), R. Chávez de Michel 2677 (LPB, NY); 4 km de Puerto Guaraní, al N frontera Paraguaya, 20°30'S, 62°15'W, 400 m, 19 Jun 1992 (fl,fr), B. Mostacedo 380 (MO). Tarija: Prov. Gran Chaco, 10 km S de Palmar Grande, camino Yacuiba-Villa Montes, 10 Sep 1977 (fl,fr), A. Krapovickas 31088 (MO); 2 km N de Palmar Grande, 38 km S de Villa Montes, 21°27'S, 63°30'W, 400 m, 10 Sep 1977 (fl), A. Krapovickas 31137 (K, MO); 0.5 km E of Chuvere, 21°32'15"S, 63°48'10"W, 870 m, 23 Mar 2007 (fl,fr), M. Nee 54876 (MO, NY).

Solanum michaelis differs from the co-occurring and morphologically similar Solanum sarrachoides and the higher elevation yungas species Solanum physalifolium in having larger anthers (2.5–3.2 mm long), while both Solanum sarrachoides and Solanum physalifolium have anthers < 2.2 mm long. Solanum physalifolium has similar shiny green-mottled berries, but occurs at higher elevations (1,400–2,900 m) in yungas or wet forest vegetation and has broadly ovate calyx lobes that partially enclose the fruit at maturity. Solanum tweedianum has similar sized anthers but a longer calyx tube (ca. 1.5–2.0 mm in flower and to ca. 5 mm or more in fruit) which fully encloses the berry both during development and at fruit maturity (Barboza et al. 2013). Solanum michaelis has similarly long calyx lobes but a shorter calyx tube in both flower (0.8–1.3 mm) and fruit (2.0–2.5 mm) that does not enclose the fruit and appears to sometimes have reflexed calyx lobes at fruit maturity (e.g., Fuentes & Navarro 2607).