Any of a class of plant hormones derived from carotenoids that function chiefly in controlling apical dominance, attracting mycorrhizal fungi to roots, and promoting seed germination. Strigolactones modulate the flow of auxins from a plant’s growing shoot tips down the stem, thereby suppressing the growth of axillary buds further down the stem. This effect is antagonized by cytokinins moving up the stem from the root, permitting the growth of axillary buds nearest the base of the stem. Strigolactones released by the roots into the soil stimulate the growth of hyphae of mycorrhizal fungi (see mycorrhiza) towards the roots—the first stage in establishing a symbiotic association with the root system. In an example of opportunistic evolution, the germination of seeds of the parasitic witchweed plant (Striga spp.), a serious pest of cereal crops in Africa, is also triggered by strigolactones.