Heliotropium
Content
Description
Annual or perennial herbs or subshrubs.
Leaves large to small, alternate, petiolate or sessile.
Inflorescences usually a unilateral, scorpioid cyme, sometimes 2 cymes close together on dichotomous branches or even a greater number of short cymes crowded together in a head-like manner, with or without bracts that may be foliose or very small and sometimes confined to lower part of cyme.
Stamens included with very short filaments.
Distribution
the warm and warm temperate zones of all continents present
A genus of about 250 species in the the warm and warm temperate zones of all continents.
Cytology
At least four basic chromosome numbers are known in the genus that are not closely related to the taxonomic position of the species from the scattered data available. There are polyploid series known from the basic numbers x = 7 and 8, while from the basic numbers x = 9, 11 and 13 only diploids were found so far.
Uses
Heliotropium indicum is reported to be used as a medicinal plant and also sometimes for the production of beverages and dyes . Heliotropium arborescens, better known under its synonym H. peruvianum, is widely cultivated as an ornamental plant and may have escaped cultivation in some places, as it is mentioned for the Malesian region, though cultivation seems to have become obsolete.
Notes
Cochranea Miers is sometimes regarded as a separate genus mainly South American in distribution, but extending to the Malesian region with Heliotropium anchusaefolium. The differences, however, do not seem to justify separation, as they are by no means more profound than those existing between subgenera and sections normally included in Heliotropium; H. anchusaefolium is the type species of section Heliophytum, moreover, and does not even belong to Cochranea.
Infrageneric classification suffers from the absence of a recent treatment including both Old World and New World species since the time of De Candolle's Prodromus. There is a lack of correspondence between the various local treatments. Malesian native and introduced species belong to sections Heliophytum, Tiaridium, Halmyrophila (= Platygyne), Heliothamnus and Orthostachys according to the most recent system of Johnston , which, however, covers South American taxa only.