Massive investments in flowers were in vain: Mass flowering after a century did not bear fruit in the bamboo Phyllostachys nigra var. henonis

Abstract Phyllostachys nigra var. henonis (Poales: Poaceae) is a tall, temperate bamboo species that has a long monocarpic life history with a flowering interval of around 120 years that is often conspicuously synchronized across a wide geographical area. Interestingly, observations of the last major flowering event, which was about a century ago, suggested that mature seeds were rarely produced as a consequence. As this bamboo has recently started flowering across Japan after a century of silence, we seek to understand its reproductive strategy by quantifying the following four issues: (1) flowering patterns within stands, (2) the presence or absence of mature seeds, (3) resource allocations to reproductive parts, and (4) asexual regrowth capacity after mass flowering. We conducted field surveys at five flowering bamboo stands in Japan. At each, many spikelets were found, but neither mature seeds nor seedlings. During the mass flowering, large amounts of resources were allocated to reproductive parts, accounting for 57% of the aboveground nitrogen pool and 63% of the aboveground phosphorus pool. These results indicate that the accumulated resources were used for flowers, but not for seed production, and thus apparently in vain. While most of the flowering ramets appeared to die, dwarf ramets (mostly less than 1 m in height) typically regenerated from the remaining belowground rhizomes and seem to be critical for maintaining the bamboo stands. This apparently inefficient sexual reproductive strategy still exists (without local extinction) perhaps due to the vigorous clonal growth system and to human‐assisted distribution.