Filamentous red-light grown gametophytes of 47 species of the Laminariales, i e about 5 0 % of all species of the order, were tested for upper survival temperature (UST, 2 wk exposure), and 42 of these species were tested for lower survival temperature (LST, 8 wk exposure) The lowest UST in the order is 19 to 20°C, encountered in the Arctic to cold-temperate species Laminaria solidungula, Alarm esculenta and Agarum cribrosum The warm temperate Japanese species Eisenia bicyclis and Undana pinnatifida have the h~g h e s t UST of 28 to 30°C The UST range in the order Laminariales, thus, spans about 10°C This 1s about 5°C less than in the related order Desn~arestiales which spans a range in UST of 15°C The largest within-family vanation in UST is found in the Alanaceae and Laminanaceae, the 2 families with most species and widest distribution The Alariaceae span a range in UST of 1O0C, the Laminariaceae of 7 to 8°C the Lessoniaceae of 5 to 6OC the Phyllariaceae of 4 "C and the Chordaceae of 3 to 4OC All gametophytes tested survlve a temperature of 1 "C for 8 w k Eleven out of 42 species do not tolerate -1 5 and/or 0 "C over 8 w k Temperature tolerance of the gametophytes coincides wlth the large-scale distribution of the species but is not crucial for distnbution llmits in most cases In addition to the temperature tolerance, the dark tolerance of fllamentous gametophytes of 12 kelp species was investigated All but 3 specles survived 18 mo of darkness