This section is from the book "Handbook Of Hardy Trees, Shrubs, And Herbaceous Plants", by W. Botting Hemsley. Also available from Amazon: Handbook of hardy trees, shrubs, and herbaceous plants.
Herbs or small shrubs with simple alternate leaves and solitary pedunculate flowers opposite the leaves. Calyx 5-lobed, persistent, and enclosing the fruit. Corolla funnel-shaped; tube often long and slender; limb 5-lobed, patent. Stamens 5, somewhat unequal, and more or less exserted. Fruit capsular, 2-celled. A small genus confined to South America, named in honour of Nieremberg, a Spanish Jesuit and naturalist. None of the species are absolutely hardy.
1. N. gracilis. - This is the beautiful slender trailing species in general cultivation at the present time. It has linear somewhat glaucous slightly pubescent leaves and very numerous pedunculate extra-axillary or terminal lilac and white flowers. It succeeds best in a light soil fully exposed to the sun.
N, filicaulis, syn. N. frutescens of gardens, is a closely allied species of erect habit with less numerous though rather larger flowers and quite glabrous foliage. N. rivularis is, a very distinct nearly hardy species of creeping tufted habit with broadly oblong obtuse long-stalked leaves and large white or pink flowers remarkable for the length of the slender tube.