every widely cultivated plant of this group is a considered useful as a companion plant. One reason is that the tiny flowers, clustered into umbels, are well suited for ladybugs, parasitic wasps, and predatory flies, which drink nectar when not reproducing. They then prey upon insect pests on nearby plants. Some of the members of this family considered "herbs" produce scents that are believed to mask the odours of nearby plants, thus making them harder for insect pests to find. Other uses The poisonous members of the Apiaceae have been used for a variety of purposes globally. The poisonous Oenanthe crocata has been used as an aid in suicides, and arrow poisons have been made from various other family species. Daucus carota has been used as coloring for butter. Dorema ammoniacum, Ferula galbaniflua, and Ferula moschata (sumbul) are sources of incense. The woody Azorella compacta Phil. has been used in South America for fuel. Toxicity Many species in the family Apiaceae produce phototoxic substances (called furanocoumarins) that sensitize human skin to sunlight. Contact with plant parts that contain furanocoumarins, followed by exposure to sunlight, may cause phytophotodermatitis, a serious skin inflammation. Phototoxic species include Ammi majus, Notobubon galbanum, the parsnip (Pastinaca sativa) and numerous species of the genus Heracleum, especially the giant hogweed (Heracleum mantegazzianum). Of all the plant species that have been reported to induce phytophotodermatitis, approximately half belong to the family Apiaceae. The family Apiaceae also includes a smaller number of poisonous species, including poison hemlock, water hemlock, spotted cowbane, fool's parsley, and various species of water dropwort. Some members of the family Apiaceae, including carrot, celery, fennel, parsley and parsnip, contain polyynes, an unusual class of organic compounds that exhibit cytotoxic effects. References Further reading Constance, L. (1971). "History of the classification of Umbelliferae (Apiaceae)." in Heywood, V. H. [ed.], The biology and chemistry of the Umbelliferae, 1–11. Academic Press, London. Cronquist, A. (1968). The Evolution and Classification of Flowering Plants. Boston: Houghton Mifflin. French, D. H. (1971). "Ethnobotany of the Umbelliferae." in Heywood, V. H. [ed.], The biology and chemistry of the Umbelliferae, 385–412. Academic Press, London. Hegnauer, R. (1971) "Chemical Patterns and Relationships of Umbelliferae." in Heywood, V. H. [ed.], The biology and chemistry of the Umbelliferae, 267–277. Academic Press, London. Heywood, V. H. (1971). "Systematic survey of Old World Umbelliferae." in Heywood, V. H. [ed.], The biology and chemistry of the Umbelliferae, 31–41. Academic