Environmental control of flowering and sex expression in Carex flava

The environmental control of flowering and sex expression has been studied under controlled environment conditions in three populations of the sedge Carex flava L. A dual floral induction requirement was demonstrated in all populations. Low temperature (< 12°C) was obligatory for, and short photoperiods strongly enhanced, primary induction and inflorescence initiation. Stem elongation and inflorescence development were promoted by long photoperiods, although most plants developed stunted flower stems also under short day (SD) conditions. Growth vigour, abundance of flowering and primary induction requirements varied widely among the populations, with critical exposure times for full flowering varying from less than 9 to about 12 weeks in SD at 9°C, and from about 9 to more than 15 weeks in long days (LD). Sex expression in the normally male terminal spike was shifted towards femaleness by marginal or incomplete primary induction. Primary induction in LD resulted in a complete change to entirely female inflorescences, whereas marginal induction in SD resulted in a similar sex reversal in some plants. The results are discussed in relation to environmental and hormonal factors known to modify sex expression in flowering plants and the significance of the results to Carex systematics and classification.