Black nightshade has been in the news recently, after its berries turned up masquerading as peas in packs of frozen vegetables.
Leaves, ripening fruit, and a flower of black nightshade, Solanum nigrum.
Black nightshade is regularly confused with deadly nightshade. Indeed, the picture in the above news story appears to be of deadly nightshade, although it is labelled black nightshade. Fortunately, deadly nightshade (Atropa belladonna) is quite rare in New Zealand, only occurring in the wild in Canterbury. Black nightshade is thought to be no where near as toxic as deadly nightshade. Nevertheless, I suspect no-one would recommend it for human consumption.
Black nightshade belongs to the genus Solanum, which also includes tomatoes (Solanum lycopersicum) and potatoes (Solanum tuberosum)!
Black nightshade (Solanum nigrum) is easily confused with small-flowered nightshade (Solanum nodiflorum, previously known in New Zealand as Solanum americanum). The former is introduced to New Zealand; the latter is thought to be native. They differ in chromosome numbers, but appear very similar externally. Barry Sneddon, one of the Botany Collection Managers, and I have been learning how to distinguish them.
Flora of New Zealand Volume 4 suggests that in:
Solanum nodiflorum (previously known in New Zealand as Solanum americanum)
* the calyx is strongly reflexed at fruiting.
* the flowers/fruit in a particular group all branch from more or less the same point.
* stone cells are evident in the fruit.
Solanum nigrum
* the calyx is not or only partially reflexed at fruiting.
* some flowers/fruit in a particular group clearly branch below the others.
* stone cells are usually absent in the fruit.
Left, unripe fruit of Solanum nodiflorum; right, ripening fruit of Solanum nigrum. The calyx of S. nodiflorum is strongly reflexed (the green triangles between each fruit and its stalk point away from the fruit). Stone cells are also just evident in the S. nodiflorum fruit, as white speckles.
As indicated by the blue arrows, the fruit (or flowers) of Solanum nodiflorum (left) branch from nearly the same point, while at least some of those of S. nigrum (right) clearly branch below the others.
From this, it appears that the plants in my garden are actually the native Solanum nodiflorum. Which, as a lover of native plants, is a good thing, I suppose. But they still look weedy…
Te Papa has a specimen collected during Captain Cook’s first expedition that has been labelled as Solanum nigrum; however, this would seem to be a mis-identification.
