Monocarpy calendars and flowering cycles in angiosperms

Simmonds, N.W.

Kew Bulletin 35(2): 235-246


ISSN/ISBN: 0075-5974
DOI: 10.2307/4114566
Accession: 005923286

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An outline of flowering cycles and their control in angiosperms is given as a preliminary to a review of long-period endogenous rhythms of flowering. There is evidence, in some tropical trees, of circa-annual cycles entrained, in some environments but not in others, to annual flowering. Monocarpy means flowering and fruiting but once in the life-cycle. Annual plants are, by definition, monocarpic but interest centers on the perennial monocarps, which are of 2 kinds: those (e.g., Ensete, Corypha and Spathelia) in which a single terminal growing point is ultimately converted into an inflorescence; and those (e.g., many bamboos and several Acanthaceae, especially Strobilanthes) in which plants are branched but nevertheless die after fruiting. For the former there is no clear evidence of exactly determined endogenous calendars but some timing device (perhaps a kind of leaf counting) is implied. For the latter, there is abundant historical-anecdotal (but not experimental) evidence of remarkably accurate endogenous calendars capable of counting time in decades. Biologically, this kind of monocarpy is to be interpreted as an adaptation that minimizes both intra-specific competition (thus contributing to the maintenance of local dominance) and pest-pressure in the reproductive phase. The underlying mechanism (as for all biological rhythms) is unknown; synchronous flowering of clonal propagules shows that it is not localized but is a diffused property of all parts of the plant. The need for experimentation is emphasized.