American black nightshade (Solanum americanum, Mill. 1768)

Identity

American black nightshade (Solanum americanum Mill., 1768), also called glossy nightshade and small-flowered nightshade, is an annual herb in the genus Solanum, family Solanaceae. In the Indian Ocean region its cooked greens are known as brède morelle. Plants of the World Online accepts the name published by Scottish botanist Philip Miller in his Gardener’s Dictionary in 1768. ¹

The epithet americanum refers to the species’ continental origin, distinguishing it from Eurasian black nightshade, Solanum nigrum, with which it is often confused in the field. The French name morelle is thought to derive from Latin morum, referring to a small dark berry, in keeping with the ripe fruits of these nightshades. ⁶

Recognition

An upright, angular stem, hairless to finely hairy and branched from the base, supports the plant. Typical height ranges from 25 cm to 1.2 m (10 in to 4 ft), with reports up to 1.5 m (5 ft) under favorable conditions. Plants growing in poor soil often remain more compact. ^{2 4}

Alternate leaves are oval to lance-shaped, measuring 4–8 cm (1.5–3 in) long and 2–4 cm (0.8–1.5 in) wide. Their edges are wavy or slightly toothed and their undersides finely hairy. White star-shaped flowers have five petals and yellow stamens joined into a cone. They open in small umbels in the leaf axils, during summer and fall in temperate climates. ²

Fruit provides a clearer recognition feature than leaf shape or stem height. Each round berry starts green with white streaks, then becomes glossy black or purple-black at full maturity. Less than 1 cm (0.4 in) across, it contains 50–100 tiny seeds. A green berry is not ripe, even when it has reached a substantial size. ^{2 4}

Useful taxonomy

Membership of the much-discussed Solanum nigrum complex explains many identification difficulties. This group contains morphologically similar species that were long confused in floras and herbarium collections around the world. Several names have been associated as synonyms with the accepted name:

• Solanum nigrum var. americanum (Mill.) O.E.Schulz (synonym)
• Solanum nodiflorum Jacq.
• Solanum ptychanthum Dunal
• Solanum patulum (L.) Roth
• Solanum nigrum var. nodiflorum (Jacq.) A.Gray

The name Solanum ptychanthum was long applied to North American eastern black nightshade, distinguished by details of the fruit and seedlings before being treated as a synonym. Without the complete scientific name, visual separation from Solanum nigrum remains uncertain even for an experienced botanist. ¹

Habitat and range

Across the Americas, POWO places the native range from southern Canada to tropical and subtropical regions. Some regional floras extend that range to Melanesia, New Guinea and Australia. Australian authorities instead document the species as introduced in their territory, a point on which sources continue to disagree. ¹

Waste ground, fallow land, field and path edges, open woodland and recently disturbed or cultivated soil all provide habitat. Humans and birds that eat the ripe berries have spread the plant widely. It now occurs through most tropical regions and many temperate ones, including mainland France, where the INPN records casual occurrence rather than established populations. ^{3 6}

Life cycle and reproduction

Germination begins a life cycle completed within one growing season: spring to fall in temperate climates and almost continuously in the tropics. Flowering continues for several months. Each pollinated flower produces a berry that takes a few weeks to change from green to glossy black. ²

Reproduction takes place solely by seed. A ripe berry contains 50–100 seeds, dispersed mainly by birds attracted to the black fruit. This prolific seed production, combined with rapid germination on disturbed ground, explains why dense colonies often appear in gardens and freshly cultivated fields. ²

Uses and risks

Several tropical cuisines use the young shoots and leaves as cooked greens, known as brède in the Indian Ocean region and associated with callaloo preparations in the Caribbean. The cooking water concentrates soluble alkaloids and is always discarded. The leaves are reported to supply nearly 6,990 mg of beta-carotene per 100 g. Fruit is eaten only when fully black and ripe, never while green. ³

Other plant parts are toxic, particularly unripe berries and raw foliage, which are rich in steroidal glycoalkaloids including solanine, solamargine and solasonine. According to the Hong Kong Hospital Authority toxic plant database, 20 mg of solanine, equivalent to about 5 g (0.18 oz) of unripe fruit, may already cause poisoning. Symptoms include nausea, vomiting, diarrhea and abdominal pain, sometimes with confusion or loss of coordination. ⁴

For the closely related Solanum nigrum, often confused with Solanum americanum, the ASPCA documents comparable toxicity to cats, dogs and horses. Ingestion can cause excessive salivation, lethargy and digestive problems. This evidence concerns that related species rather than a separate veterinary assessment of American black nightshade. ⁵

Varieties, look-alikes and related plants

Horticultural cultivars are not recognized for Solanum americanum. It is a spontaneous wild plant, never selected for ornamental use. ³

Eurasian black nightshade, Solanum nigrum, is the main look-alike because its fruits and seedlings are almost identical. Another potentially confusing name is Solanum ptychanthum, now treated as a synonym but still used in some North American floras. Geographic distribution combined with examination of the seed is needed to resolve these names and plants, beyond a simple look around the garden. ¹

When the exact identity of a wild plant remains uncertain, the same precaution applies wherever it grows: never eat a green berry. Culinary use should be limited to fully black or purple berries from a plant identified with certainty.

Main sources

• Plants of the World Online / Kew, Solanum americanum Mill.
• North Carolina Extension Gardener Plant Toolbox, Solanum americanum
• Plants For A Future, Solanum americanum
• Hospital Authority (Hong Kong) Toxic Plant Database, Solanum americanum
• ASPCA, Black Nightshade (Solanum nigrum) toxicity entry
• INPN / MNHN, Solanum americanum Mill., 1768 - American black nightshade
• Tela Botanica / eFlore bdtfx, Solanum americanum Mill.
• USDA PLANTS Database, Solanum americanum (symbol SOAM)