The coast redwood may be a hybrid of its two surviving cousins
Only three redwood species survive, and one of them looks like the child of the other two. Genetic trees place the coast redwood beside the dawn redwood on one gene and beside the giant sequoia on another, hinting at an ancient hybrid. All three are now listed as endangered, and wildfires recently killed about a fifth of the giant sequoias.
The redwoods form a subfamily of the cypress family and include the largest and tallest trees on Earth. The coast redwood grows along northern California and the far south of Oregon, the giant sequoia on the western slopes of the Sierra Nevada, and the dawn redwood in south-central China. The first two are evergreen giants that can live for thousands of years. The dawn redwood sheds its leaves, stays comparatively small, and tolerates colder climates.
Gymnosperms rarely duplicate whole genomes, yet the coast redwood is hexaploid, carrying six chromosome sets for a total of 66. Yang and colleagues compared two single-copy nuclear genes, LFY and NLY, and got conflicting family trees, one grouping it with Metasequoia and the other with Sequoiadendron. Their analysis favoured a hybrid origin involving both, a case of reticulate evolution. Because the lineages reach back to the Jurassic, pinning down exactly when that happened is difficult.
Fossils make the group very old. Sequoia jeholensis comes from Jurassic rocks, and a late Triassic fossil wood from China resembling the giant sequoia may push the origin into the Norian stage. In the Cretaceous, redwoods spread across the Arctic Circle, Europe, North America and Asia. Cooling from the late Eocene and later ice ages pushed them back into small refuges. A 2021 molecular study found their closest relatives are the Athrotaxidoideae, now confined to Tasmania, with the split dating to the Jurassic.
The IUCN lists all three living species as endangered, citing logging, fire suppression and burl poaching among the threats. Giant sequoias need fire in their life cycle, yet in 2024 it was reported that extreme blazes had killed around one in five of them over two years, possibly intensified by decades of suppressing regular burns. Britain, meanwhile, holds roughly 500,000 redwoods, mostly grown from Victorian-era seeds and seedlings shipped from the United States.
Source: Sequoioideae
