<jats:p>The structure and absolute configuration of heterocladol, C15H26BrClO (6), have been determined by single-crystal X-ray diffraction methods. This compound is the first example of a selinane skeleton reported from Laurencia species and its structure can be rationalized in terms of a trans-annular ring closure of a germacradiene. The colourless crystals are monoclinic, space group P21, with a 11.852, b 14.486, c 10.932 Ǻ, β 119.6�, Z4.