GERMINATION ECOPHYSIOLOGY OF AN EASTERN DECIDUOUS FOREST HERB STYLOPHORUM-DIPHYLLUM

S. diphyllum (Michx.) Nutt. is an herbaceous polycarpic perennial that grows in mesic deciduous forest from western Pennsylvania [USA] and southern Ontario [Canada] to Wisconsin south to southwestern Virginia, northern Alabama, northern Arkansas and Missouri [USA]. Seeds are dormant at dispersal in late May and early June. Dormancy is due to a rudimentary (i.e., underdeveloped) embryo which requires incubation at low moist temperatures (stratification) for growth. In the habitat, embryo elongation occurs during the cold season and seeds germinate in early spring. A warm pretreatment is not required for subsequent embryo growth and germination. Embryos in freshly matured seeds averaged 0.41 mm long but after 10 wk of chilling at 5.degree. C they averaged 1.41 mm. Germination of seeds incubated continuously at 5.degree. C began after 11 wk and after 19 wk 80% had germinated. Seeds stratified for 6 wk and then transferred to (12/12 h) daily thermoperiods of 15.degree./6.degree. and 20.degree./10.degree. C germinated to 75 and 65%, respectively: 12 wk of stratification were required before a comparable percentage of seeds would germinate at 25.degree./15.degree. C. Seeds of S. diphyllum fit Nikolaeva''s definition of morphophysiological complex dormancy.