The Developmental Pattern in a Group of Therophytes: II. Vernalization and Photoperiodic Induction

Abstract

The occurence and characteristics of vernalization and photoperiodic floral induction in a group of therophytes( Alyssum calycinum L., Arenaria serpyllifolia L., Calamintha acinos (L.) Clairv., Lamium amplexicaule L., Lithospermum arvense L., Medicago minima (L.) Grufbg., Myosotis hispida Schlecht., Thlaspi perfoliatum L.) growing in xerothermic grasslands in the Bohemian Karst and České Stredohori Hills, has been studied. Obligatory vernalization requirement in all the studied species, with exception of Lamium amplexicaule , was found. The plants could be arranged into the two sets according to their photoperiodic reaction: facultative long days plants- Alyssum calycinum with strong LD requirement, Arenaria serpyllifolia, Myosotis hispida, Thlaspi perfoliatum and Lamium amplexicaule (the last three species being practically neutral), and obligatory long day plants Lithospermum arvense and Medicago minima , and most probably also Calamintha acinos. The presented results are in a good agreement with phenological observations of flowering time of the plants in their natural habitats. All these developmental features, along with the seed dormancy, represent general adaptation to local climatic pattern in the investigated therophytes. Vernalization seems to be most important adaptation, preventing the autumn flowering. The early spring flowering is based upon the absence (or weakly expressed) photoperiodic reaction. Only in the late flowering species exerts LD photoperiodic reaction obligatory character.