Heliotropium

Genus of flowering plants in the borage family Boraginaceae

Heliotropium ,/h//iː//l//i//ə/'/t//r//oʊ//p//i//əm//, // //l//i//oʊ// / is a genus of flowering plants traditionally included in the family Boraginaceae s. l., but placed in the family Heliotropiaceae within the Boraginales order, by the Boraginales Working Group There are around 325 species in this almost cosmopolitan genus, which are commonly known as heliotropes. They are highly toxic to dogs and cats, as well as to humans.

The name "heliotrope" derives from the old idea that the inflorescences of these plants turned their rows of flowers to the Sun. Ἥλιος (helios) is Greek for "Sun", τρέπειν (trepein) means "to turn". The Middle English name "turnsole" has the same meaning. A Classical myth, told in Ovid's Metamorphoses, imagines that the water nymph Clytie, in love with the sun god Helios, was betrayed by him. Wasting away, she transformed into the heliotrope, whose flowers supposedly always face the Sun.

Like other members of the Heliotropiaceae, plants in the genus Heliotropium have 5 merous, tetracyclic flowers and actinomorphic corollas. They likewise share in their characteristic terminal styles and highly modified stigmatic heads (basal stigma, infertile apex). Species in the genus are typically herbs or subshrubs exclusively and are characterized by their dry fruits that divide into two or four mericarpids.

Heliotropes are popular garden plants, most notably garden heliotrope (H. arborescens). Some species are weeds, and many are hepatotoxic if eaten due to abundant pyrrolizidine alkaloids. There have been cases of canine death due to over ingestion of this toxic plant. Some danaine butterflies, such as male queen butterflies, visit these plants, being attracted to their pyrrolizidine alkaloids. Though it is not palatable and most animals will completely ignore it, there have been cases of horses, swine and cattle being poisoned due to contamination of hay. Caterpillars of the grass jewel (Freyeria trochylus), a gossamer winged butterfly, feed on H. strigosum. The sap of heliotrope flowers, namely of European heliotrope (H. europaeum), was used as a food coloring in Middle Ages and Early Modern French cuisine. One of the most famous ragtime piano melodies is "Heliotrope Bouquet", composed in 1907 by Louis Chauvin (the first two strains) and Scott Joplin (the last two strains). Garden heliotrope is grown in Southern Europe as an ingredient for perfume. The purplish facial rash of dermatomyositis is called "heliotrope rash" because it resembles E. arborescens.

Seeds of the Heliotropium genus were discovered in the 1940s and 50s to be responsible for liver disease in populations that consumed them in large quantities, either inadvertently (as a contaminant of food crops) or deliberately (associated with the ingestion of herbal infusions for the treatment of certain ailments). The seeds contained high concentrations of pyrrolizidine alkaloids, identified mainly as the N oxide of heliotrine (74%), and one or two other compounds similar in character to lasiocarpine. More recently, in 1993 and 2017, there have been reported cases of poisoning in Tajkistan from wheat contaminated with Heliotropium lasiocarpum seeds.

Taxonomic revision supported through molecular phylogenetics led to the recognition of Euploca as genus separate from Heliotropium. Heliothamnus diversification is estimated to have taken place in the late Miocene. The age of Heliothamnus suggest that its diversification could have been triggered directly by the uplift of the Andes, something that would have promoted speciation in inner Andean valleys and the Andean scrub. The majority of endemic Heliothamnus taxa in the region are restricted to these sorts of environments, further supporting this theory as the current leading theory explaining Heliothamnus diversification.