Osmorhiza aristata is a herbaceous polycarpic perennial that grows primarily from Japan, through southern China, to the Himalayas. It is related closely to the central and eastern North American species O. claytonii and O. longistylis. Together, the distribution of the three species represents an example of the well-known Asian-North American pattern of disjunction. Requirements for dormancy-break and embryo growth were determined for seeds of O. aristata collected in Japan during summers 1998 and 1999. Embryos in fresh seeds were 0.48 mm long, and they had to grow to 9 mm before the radicle emerged from the mericarp. Embryo growth and germination occurred during cold stratification at 5 C, which was the optimum temperature for germination. A warm (30/15 C) stratification pretreatment was not required for seed germination at 5 C, and gibberellic acid (GA3) did not substitute for cold stratification. Thus, O. aristata seeds have deep complex morphophysiological dormancy (MPD). In contrast, seeds of O. claytonii and O. longistylis have nondeep complex MPD, i.e., they require warm followed by cold stratification to germinate and GA3 overcomes dormancy (Baskin & Baskin 1984, 1991). The type of MPD in seeds of O. aristata is identical to that in seeds of western North American populations of O. berteroi (chilensis) and O. occidentalis (Baskin et al. 1995). Although closely-related, Arcto-Tertiary relict congeners often exhibit high morphological similarity (stasis), the taxa may differ vastly in their physiological traits, such as seed dormancy.

Key words: Apiaceae, Arcto-Tertiary, Japan, North America, Osmorhiza aristata, seed germination