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.
This is a small order intermediate in characters between the last and the next following. The species are herbaceous or woody erect or prostrate plants with alternate simple ex-stipulate leaves and showy flowers. Calyx deeply 5-lobed, valvate in aestivation. Corolla funnel-shaped or salver-shaped, with a plaited aestivation. Stamens 5, equal, alternating with the lobes of the corolla. Fruit of 5 or more distinct or partially confluent nuts enclosed in the persistent calyx; nuts by abortion usually only one-seeded. Seeds albuminous. There are six genera and about thirty-five species belonging to this order. All natives of South America.