Evolutionary Origin of Prolonged Delayed Fertilization in the Fagaceae.
Shagawa T, Myotoishi C, Yahara T, Imai R, Deng M, Satake A.
Phenology
Every acorn you see forming on an oak this summer may actually be the result of a pollination event from last year — a biological clock so ancient it predates the split between oaks and their relatives, and understanding it helps explain why some oak mast years are so unpredictable.
Most flowering plants pollinate and set fruit within one growing season, but many members of the oak family take a full two years from flower to finished fruit. Scientists studied 88 species across the entire oak family tree and discovered this slow approach evolved just once in a shared ancestor, then was lost and abandoned in several branches like chestnuts and some oaks. Interestingly, the ancestral plants were insect-pollinated and evergreen — but those traits didn't actually drive the switch to the two-year strategy.
Key Findings
The two-year fruiting strategy evolved just once in the common ancestor of most Fagaceae (excluding beech and Trigonobalanus), making it an ancient single-origin trait.
At least three lineages — Castanea (chestnuts), Quercus (oaks), and Castanopsis (chinkapins) — independently reversed back to the faster one-year fruiting cycle.
Insect pollination and evergreen leaf habit were ancestral to the subfamily Quercoideae, but neither trait statistically drove transitions in fruiting strategy, suggesting the two-year delay evolved and is maintained by other selective pressures.
chevron_right Technical Summary
Researchers traced the evolutionary history of a quirky reproductive strategy in the oak family (Fagaceae), where some species wait an entire extra year between pollination and fertilization. They found this "slow fruiting" evolved once in a common ancestor and has been lost multiple times independently in groups like oaks, chestnuts, and chinkapins.
Abstract Preview
The temporal organization of flowering, fertilization, and fruiting is a fundamental axis of life-history evolution in angiosperms. While most species complete fruit development within a single gro...
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An oak is a hardwood tree or shrub in the genus Quercus of the beech family. They have spirally arranged leaves, often with lobed edges, and a nut called an acorn, borne within a cup. The genus is widely distributed in the Northern Hemisphere, with some 500 species, both deciduous and evergreen. ...