Solanum americanum is a non-native plant in the same genus as Solanum nelsonii, native to but extinct on Kure. Solanum americanum is widespread but not abundant and shares with Verbesina characteristics such as broad serrated (saw-toothed) leaves. It can be found year-round but germinates in abundance in the winter.
Solanum cotyledons are ovate to lanceolate (lance-shaped), usually with sharply pointed tips, and are densely pubescent (hairy), especially in the margins (edges). They often grow at some angle less than 180 degrees from each other. These characteristics make them fairly distinctive from other plants on Kure.
Solanum produces subsequent leaves singly, not in pairs, so that the youngest leaf is always small compared to its opposite leaf. The true leaves are ovate to nearly round when young, but become more pointed as they grow out. Some hairs on the true leaves are much more coarse.
At later stages, the leaf margins develop dentition. Solanum teeth tend to be more rounded than in Verbesina, and more regular than in Chenopodium. The leaves still bear stiff white hairs, though they are much less densely spaced than on young leaves. The leaf shape is also very similar to Chenopodium but which has a slightly more squared-off base and irregular dentition. The base of Solanum leaves tends to be fairly rounded with a flanged stem. See the Verbesina section for leaf comparisons.
In addition to broader, more rounded teeth, S. americanum leaves (below left) have a slightly flanged stem. S. american leaves are also alternate (branching singly from different sides of the stem) versus an opposite (branching in pairs from opposite sides of the stem) on Verbesina (below right).
Description: Annual or short-lived perennial herbs up to 1.2 m tall, erect or wide-spreading, straggly with age, sometimes flushed purplish; stems sometimes angled or narrowly winged with lines of tissue from the base of petiole, the wings smooth or with sort soft teeth, unarmed, glabrous or sparsely pubescent with simple curbed hairs. Leaves simple, alternate, ovate to ovate-lanceolate, margins entire or with up to 8 short, blunt, rounded lobes, sinuses shallow and rounded, greatly variable in Solanum americanum (PIER species info) http://www.hear.org/pier/species/solanum_americanum.htm . Size, up to 10 cm long on young growth and up to 2 long on aged distal twigs, usually ca. 6 cm long and 3 cm wide, apex acute to acuminate, base truncate to cuneate and continued as a narrow wing along petiole, petioles 1-4 cm long. Flowers perfect, actinomorphic, in extra-axillary umbelliform cymes, peduncles 1-2.5 cm long, flowers congested at apex, pedicels 5-8 mm long; calyx campanulate, 1-2 mm long, the lobes obtuse, ca. 1 mm long; corolla white or occasionally purple-tinged, stellate, 0.8-0.9 cm in diameter, with a yellowish-green star-shaped area, the lobes ca. 1.5 mm wide; stamens inserted near base of corolla tube; filaments with spreading hairs on inner side, 1-2 mm long; anthers oblong, 1.5-2 mm long, opening by pores or short slits; ovary globose, ca. 1 mm in diameter, glabrous; style erect, 2.5-4 mm long, pubescent in lower part; stigma capitate, at level of anther pores. Berries glossy black, succulent, readily shed when ripe, sclerotic granules 0-4, ca. 0.5 mm in diameter, pedicels erect or recurved in fruit, up to 4 cm long, calyx somewhat enlarged and often reflexed. Seeds numerous, 1-1.5 mm long, compressed, testa minutely reticulate (Wagner et al., 1999; pp. 1268-1269).