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 undershrubs with alternate petiolate leaves and lateral or terminal circinate cymes of small blue or white flowers. Corolla funnel- or salver-shaped, with a plicate limb. It differs from all the preceding genera in having the nuts consolidated, but eventually separating, and 1-seeded. There is one European species, and several others from the warmer and tropical parts of both the Old and New Worlds. The name is from the sun, and a turning, in allusion probably to the form of their inflorescence.
1. H. Peruvianum. Turnsole or Cherry-pie. - This tender dwarf shrub is so well known that description would be superfluous. The agreeable scent of its lilac or dark blue flowers forms its principal recommendation. There are now many varieties in cultivation, varying in every shade from white to a rich dark blue and violet, or white and blue. H. grandiflorum, differing mainly in its larger foliage and flowers, is probably the parent or co-parent of some of these varieties. The only objection to the second species is its comparatively scentless though larger flowers. The variety commonly seen in gardens under the name of Voltaireanum should be Volterrianum, after the village of Volterra in Italy.
H. suaveolens is a beautiful hardy annual species from the Caucasus, with white highly fragrant flowers. It appears to be almost unknown in this country, but in Russian gardens it takes the place of the Peruvian species.
Tournefortia heliotropoides is an allied hardy suffruticose perennial from South America with violet-blue flowers.