Solanum monadelphum Van Heurck & Müll.Arg.

  • Authority

    Knapp, Sandra D. 2002. section (Solanaceae). Fl. Neotrop. Monogr. 84: 1-404. (Published by NYBG Press)

  • Family

    Solanaceae

  • Scientific Name

    Solanum monadelphum Van Heurck & Müll.Arg.

  • Type

    Type. Peru. San Martin: Prope Tarapoto, 1855-1856, Spruce 4051 (lecto-type, G, designated here; isolectotypes, AWH-n.v., BM, C, G-DC, K, MPU).

  • Description

    Species Description - Small shrubs of river courses, 1-1.5 m tall; young stems puberulent with appressed reddish uniseriate papillate trichomes ca. 0.1 mm long; young leaves glabrous and somewhat shiny, occasionally with a few trichomes like those of the young stems; olders stems glabrate, the bark reddish-gray. Sympodial units plurifoliate. Leaves borne in whorl-like clusters along the stems, lanceolate to oblanceolate, very rarely geminate, widest at or distal to the middle, glabrous on both surfaces, sessile, 6-20 x 0.8-4.5 cm, with 6-8 pairs of main lateral veins, these prominent and yellow beneath, the apex acute, the base sessile, attenuate and decurrent onto the stem. Inflorescences terminal, later becoming lateral, often many-times branched, glabrous, 1.5-5 cm long, 5-20-flowered; pedicel scars irregularly spaced 0.5-1.5 mm apart. Buds completely enclosed in the calyx until quite late, when young appearing somewhat caudate from the elongate calyx tube, later globose, then ellipsoid after corolla exsertion. Pedicels at anthesis thick, erect, and white, 0.7-1.1 cm long, tapering from the base of the calyx tube to a base 0.5-1 mm diam. Flowers with the calyx tube cup-shaped, constricted at the base, 1.5-2.5 mm long, the lobes irregularly deltoid, 2.5-3 mm long, glabrous and appearing woody in dry material, fleshy in live plants; corolla white and fleshy, 1.5-2 cm diam., lobed 2/3 of the way to the base, the lobes planar at anthesis, the tips and distal 1/3 of the margins of the lobes densely papillose; anthers 3.5-4.5 x 1-1.5 mm, poricidal at the tips, the pores teardrop shaped; free portion of the filaments 0.5-0.75 mm long, the filament tube 1-1.5 mm long; ovary glabrous; style straight, 7-9 mm long; stigma merely a widened area on the tip of the style, the surface minutely papillose. Fruit a globose, green berry, becoming yellowish when ripe, 0.8-1 cm diam.; fruiting pedicels woody, erect, 0.5-1.2 cm long, 1-2 mm diam. at the base; calyx lobes accrescent and woody in fruit, ca. 5 mm long. Seeds dark brown in dry material, pale tan in live plants, ovoid-reniform, 3-3.5 x 1-1.5 mm, the surfaces minutely pitted. Chromosome number not known.

  • Discussion

    Solanum monadelphum is closely related to S. sessile, also of eastern Peru, but is easily distinguished from that species by its narrow, willow-like leaves, plurifoliate sympodial units, and riverbed habitat. The buds of the two species are nearly identical, and the inflorescence structure is quite similar. In the area around Quincemil (Peru, Cuzco, Quispicanchis), intermediates between the local form of S. sessile and S. monadelphum are common. The intermediates are usually found growing in the water with typical S. monadelphum plants. This could represent local variation in S. monadelphum or hybridization between the two species. Solanum monadelphum and S. sessile are sympatric in other parts of their ranges, but I have seen intermediates only in the Quincemil area.

    Solanum monadelphum is one of the most ecologically striking members of sect. Geminata. It is a shrub of river beds, growing on gravel or sand banks, and is subject to periodic inundation, particularily in the wet season, when the plants may spend many days underwater. The narrow leaves of S. monadelphum are related to this habitat. Three other species also growing in river beds, but not necessarily closely related to S. monadelphum (S. palmillae, S. imberbe of the S. deflexiflorum species group, S. amnícola of the S. arboreum species group), share this leaf shape. Solanum monadelphum is common where it occurs, forming dense knee-high thickets along riverbanks in local areas.

  • Distribution

    Throughout eastern Peru along river courses, from 250 to 500 m.

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