Solanum arboreum
Citation:
Solan. syn. 20. 1816.
Type:
Venezuela. Sucre: Cumanacoa, Humboldt & Bonpland s.n. (holotype, P-Bonpl. [microfiche IDC 6209-2:61 I.6]; isotype, B-W [F neg. 2889]).
Last edited by:
Knapp, S.
Written by:
Knapp, S.
Habit:
Rhizomatous shrubs to treelets, 0.5-3 m tall; young stems and leaves densely puberulent with appressed uniseriate trichomes 0.1-0.3 mm long, these reddish or somewhat golden; older stems glabrate, rather thick; bark of older stems greyish and peeling.
Sympodial structure:
Sympodial units difoliate, geminate.
Leaves:
Leaves obovate, sometimes elliptic, widest at the middle or in the distal third of the leaf blade, glabrous on both surfaces, in Central American material occasionally with scattered minute uniseriate or unicellular trichomes along the midrib beneath; major leaves 8-28 x 4-13 cm, with 7-12 pairs of main lateral veins, these impressed above, prominent and reddish in dry material beneath, the apex acute to acuminate, the base acute, often oblique, to somewhat auriculate in Costa Rican material; petioles 0.3-2 cm long; minor leaves differing from the major ones in size and shape, orbicular to elliptic, 1.5-9 x 1.4-6 cm, the apex acute, the base rounded; petioles 2-3 mm long.
Inflorescences:
Inflorescences opposite the leaves, simple, 0.2-4 cm long, puberulent with the same appressed uniseriate trichomes as those of the young stems and leaves, 5-30-flowered, but only bearing one or two at a time; pedicel scars closely spaced and overlapping, beginning at the base of the inflorescence. Buds globose when young, later ellipsoid with the exsertion of the corolla, if the calyx lobes are long-triangular, these appearing somewhat caudate in bud. Pedicels at anthesis deflexed, 0.4-1 cm long (rarely shorter), tapering from the calyx to a slender base ca. 0.5 mm in diam.
Flowers:
Flowers with the calyx tube conical, 0.75-1 mm long, the lobes variable, deltoid to long-triangular, 0.5-2 mm long, glabrous or puberulent with the appressed, often golden, trichomes of the rest of the inflorescence; corolla white, 0.6-1.5 cm in diam., lobed 3/4 of the way to the base, the lobes planar or reflexed at anthesis, the tips and margins of the lobes minutely papillose; anthers 1.5-4 mm long, poricidal at the tips, the pores tear-drop shaped; free portion of the filaments 0.25-0.5 mm long, the filament tube 0.25-0.5 mm long; ovary glabrous; style straight, in short-styled flowers 1-1.5 mm long, in long-styled flowers 3-6 mm long; stigma a broadened area on the tip of the style, the surface minutely papillose.
Fruits:
Fruit a globose, green berry (red fide Haught 2850), 1-1.5 cm in diam.; fruiting pedicels erect and woody, 0.8-2 cm long, varying in length even on a single plant and in a single locality, the surfaces rough and rather corky, 1-1.5 mm in diam. at the base.
Seeds:
Seeds pale yellowish-tan, ovoid-reniform, 3-4 x 1.5-2.5 mm, the surfaces minutely pitted.
Distribution:
Widely distributed in northern South America and western Central America from Costa Rica to Trinidad and Tobago, at low to middle elevations, generally in wet places.
Phylogeny:
Solanum arboreum is a member of the Solanum arboreum species group (Knapp, 2002) of the Geminata clade (Bohs, 2005).
References:
Knapp, S. 2002. Solanum section Geminata (G. Don) Walpers (Solanaceae).
Flora Neotropica 84: 1-405.
Bohs, L. 2005. Major clades in Solanum based on ndhF sequences.
Pp. 27-49 in R. C. Keating, V. C. Hollowell, & T. B. Croat (eds.), A festschrift for William G. D’Arcy: the legacy of a taxonomist. Monographs in Systematic Botany from the Missouri Botanical Garden, Vol. 104. Missouri Botanical Garden Press, St. Louis.
Solanum arboreum is a misnomer since this species is usually a small shrub and is often rhizomatous. I returned to the type locality to re-collect this plant, and found plants corresponding exactly to the type in the Humboldt and Bonpland herbarium, but all were rhizomatous shrublets. Humboldt and Bonpland may have made a mistake in transcribing their field notes, or perhaps this species occasionally does occasionally attain tree size in the area. Near Cueva El Guácharo in Monagas, Venezuela, all of the plants growing in a 3x3 m square plot were interconnected by rhizomes. Solanum arboreum is also rhizomatous at Finca La Selva, Costa Rica, and in the Canal Area, Panama. In all these areas the plants are growing in waterlogged or clay soils and the habit is perhaps correlated with this environmental condition. The only other species of section Geminata I have seen with this habit is S. robustifrons of eastern Peru.
Solanum arboreum is extremely variable in leaf shape, particularly in the shape of the leaf base. In northern South America, the leaves are petiolate, while in Costa Rica, they are nearly sessile, and the base is somewhat cordate. The character transistion is relatively abrupt and occurs in the vicinity of the Canal in Panama. Those collections with nearly sessile leaves often have long-acuminate calyx lobes, but this character extends into populations with petiolate leaves. The name S. enchylozum has been used for those plants with long-acuminate calyx lobes and sessile leaves. In conditions of severe root crowding (in small pots in the greenhouse) and water stress, individuals of S. arboreum develop even more extremely sessile leaves and crowded internodes. The morphological differences therefore may be at least partially environmentally controlled.
Solanum arboreum is most likely related to S. ramonense of high elevation Panama and Costa Rica, sharing with that species papillate new growth, short inflorescences with densely packed pedicel scars, green berries on erect pedicels, and tiny white flowers with reflexed petals. Both of these species are apparently andromonecious, with both long-styled and short-styled flowers (mentioned by Schulz in his description of S. dolichostylum). Few berries are borne on any given inflorescence, and these are usually near the base.
I have chosen to lectotypify the name Solanum dolichostylum O. E. Schulz, a synonym of S. arboreum, with the the first of the collections cited by Schulz in the original description, neither of which are presently extant at B. I have been unable to locate any duplicates of Hart 6779 from Trinidad, and prefer therefore to designate as the lectotype a collection that I have seen, Eggers 5797.