Flowering phenology of the nine-year plant, Strobilanthes cernua (Acanthaceae)

Abstract

Strobilanthes cernua Bl. (Acanthaceae) has been generally recognized to flower every nine years. However, no mechanism is known for its plietesial flowering, i.e., pluriannual and monocarpic flowering with a period of several (or sometimes decades) years. To know how this species determines the year to flower under a mountain forest in the wet tropics, we cultivated a seedling and its clonal propagates under artificial growth conditions until flowering. One individual started flowering under controlled culture room seven years after the germination; another individuals transplanted to different culture conditions started to bloom eight years after the germination. We also found many ‘irregular’ flowering in this species from herbarium records and our own field surveys on a particular locality in West Java, Indonesia, suggesting that the flowering cycle is not exactly nine years. Based on these observations, two possible interpretations of the nature of the flowering phenology are discussed.