1. Heliotropium L. (heliotrope)

Plants annual or perennial herbs (shrubs elsewhere). Stems usually branched, often hairy, the hairs often lacking pustular bases, sometimes glandular. Leaves alternate or opposite, well-developed, sessile or short-petiolate. Stipules absent. Leaf blades simple, the margins entire or sometimes wavy, occasionally rolled under, the surfaces usually hairy, the hairs occasionally with persistent pustular bases (with calcified or silicified walls, known as cystoliths) and roughened to the touch, sometimes glandular. Inflorescences of solitary terminal flowers or more commonly terminal and sometimes also axillary spikes (sometimes appearing as dense clusters when young), these often appearing coiled (scorpioid) and uncoiling as the flowers develop, the flowers then all oriented toward the upper side of the axis, sometimes subtended by bracts. Flowers more or less actinomorphic, hypogynous, perfect; cleistogamous flowers absent. Calyces usually deeply 5-lobed, the lobes equal or unequal, persistent at fruiting. Corollas usually shallowly 5-lobed, saucer-shaped or funnel-shaped to trumpet-shaped, the inside of the throat often hairy but lacking appendages. Stamens 5, the filaments attached in the corolla tube, short, the anthers exserted, attached at their base, usually yellow. Pistil 1 per flower, of 2 fused carpels. Ovary not or only shallowly 4-lobed, 4-locular, with 1 ovule per locule, the placentation axile or sometimes appearing nearly basal. Style 1 or absent, situated at the tip of the ovary, usually not persistent at fruiting, the stigma usually with the receptive area in a band around the basal portion, crowned by a variously shaped sterile appendage. Fruits dry and drupelike (occasionally schizocarps elsewhere), unlobed or more commonly 2- or 4-lobed, usually separating (sometimes tardily) into 2 or 4 nutlets, these 1- or 2-seeded, glabrous or hairy, dark green to nearly black. Variously 260–420 species (depending on the generic circumscription), nearly worldwide, most diverse in tropical and warm-temperate regions.

Several species of heliotropes are cultivated widely as garden ornamentals. However. many species are noxious weeds and contain toxic pyrrolizidine alkaloids that can be a hazard to livestock (Burrows and Tyrl, 2001). Some species have been investigated for possible pharmaceutical value in the treatment of tumors (Al-Shehbaz, 1991).