There are advantages to synchronizing flowering, including the benefits of cross-pollination and dilution of herbivory. Some species achieve such synchrony through irregular (mast) flowering that depends on an environmental cue. Frasera speciosa (Gentianaceae; monument plant, or green gentian) is a long-lived monocarpic herbaceous perennial found commonly in the Colorado Rocky Mountains. It grows for many years (possibly over 100 years in alpine populations) as a basal rosette before producing a large inflorescence (as tall as 3m at lower altitudes) in its final year. It is mast flowering, with 2 – 7 years between flowering events, which I have tracked for 41 years in an annual count of flowering plants along a 14.5-km transect through the upper East River valley. Plants preform both leaves and inflorescences, with approximately four times as many pre-formed leaves as current leaves, which suggests that inflorescences are also pre-formed.
Results/Conclusions
In a search for an environmental cue that might synchronize flowering, I included lag times of up to four years, and found a strong correlation (r2 = 0.660. p<.0008) between May – July precipitation and number of plants flowering four years later (n = 12 years with >1,000 inflorescences, range up to 31,117). This cue has effects over large geographical areas, synchronizing flowering events over a broad region of the plant’s range in the Rocky Mountains. Herbivory of flower stalks by a specialist Pallopterid fly and mule deer could be one factor selecting for the periodic mast flowering, and opportunities for cross-pollination may too (although plants can self-pollinate through geitonogamy). As the climate changes, and historical precipitation patterns change, the environmental cue for flowering in this species may change its frequency and strength, potentially altering the pattern of flowering. The insights gained by this study are only possible with a commitment to a decades-long research program, which is facilitated by work at a field station (Rocky Mountain Biological Laboratory).