Wintering forms of perennial herbs in the cool temperate regions of Japan

Abstract

Wintering forms of 42 perennial herbaceous species were investigated in the cool temperate regions of Japan. Three types of dormancy were recognized based on the number of days required for growth initiation at 24 °C: nondormant (< 8 days), shallow dormant (17–59 days), and deep dormant (> 300 days). The nondormant herbs overwinter under an imposed dormancy, as in biennials. The shallow-dormant herbs required a greater number of days for growth initiation as incubation temperature decreased and thereby could avoid unseasonal autumn sprouting. The deep-dormant herbs required the greatest number of days for growth initiation under a wide range of temperatures, and they seldom sprout new shoots during the unfavorable season. Three types of winter buds were recognized based on the degree of differentiation of scales from young foliage leaves: buds with no differentiated scales, buds with partially differentiated scales, and buds with perfectly differentiated scales. The herbs with perfectly differentiated scales tended to expand a small number of foliage leaves that were performed in the buds. Two contrasting wintering forms occurred in relation to habitats. The nondormant herbs with no differentiated scales on the groud surface (hemicryptophytes) were found in exposed habitats. The deep-dormant herbs with perfectly differentiated scales under the ground surface (geophytes) were found on the forest floor. The ecological implications of these wintering forms are discussed.