Herbarium specimens (over 400) of all the 64 species of Alyssum listed in the Flora Europaea were analysed for their nickel and cobalt content in order to identify hyperaccumulators (> 1000 $\mu $g/g dry mass) of either element. In addition to the three previously recorded hyperaccumulators of nickel (A. bertolonii, A. murale and A. serpyllifolium s.sp. lusitanicum), a further 11 were identified. With the exception of A. fischerianum, all hyperaccumulating species are from Section Odontarrhena of the genus and include A. alpestre, A. argenteum, A. corsicum, A. euboeum, A. fallacinum, A. heldreichii, A. markgrafii, A. robertianum, A. smolikanum and A. tenium. Nickel contents exceeding 10000 $\mu $g/g (1%) were recorded in A. bertolonii, A. corsicum, A. heldreichii, A. markgrafii and A. robertianum. The occurrence of 14 hyperaccumulators in a single genus is the highest density so far recorded and poses interesting questions concerning the plant chemistry of these species.