The world's tallest tree species also hides a record-sized genome
Coast redwoods have topped 116 metres, taller than any other living tree, and can live around 2,000 years. Hidden inside is another giant: a six-fold set of chromosomes and, per Guinness, the largest genome of any plant examined up to 2020, some 26.5 billion letters of DNA.
Sequoia sempervirens is the only surviving species in its genus, a member of the cypress family. Typical adults stand 60 to 100 metres, with trunks up to about 9 metres across and soft, fibrous bark as thick as 35 centimetres that shows bright red-brown when freshly exposed, hence the common name. Genetically it is odd among conifers, a hexaploid with 66 chromosomes, and both its mitochondrial and chloroplast DNA come from the father. A 2010 study by Yang and colleagues proposed that the species began long ago as a cross between the forebears of the dawn redwood and the giant sequoia, though fossils reaching back to the Jurassic make the story hard to pin down.
The Scottish botanist David Don first named it Taxodium sempervirens in 1824, the evergreen relative of the leaf-shedding baldcypress, and Stephan Endlicher coined the genus Sequoia in 1847 without ever explaining the name. Before logging took off in the 1850s, redwoods covered an estimated 810,000 hectares of coastal California and a corner of Oregon. Today they cling to a strip about 750 kilometres long, from Monterey County to just over the Oregon line, favouring foggy valleys with year-round streams. Salty ocean winds stunt them, and on poor soils in Mendocino's pygmy forest ancient trees stay dwarfed.
The range has shifted before. Redwood bark in the La Brea Tar Pits shows the trees grew near Los Angeles 25,000 to 40,000 years ago, and a fossil stump on an Oregon beach sits 160 miles north of today's limit. Its knack for resprouting from the root crown after fire or felling has earned it a reputation as a carbon-storage champion, and a Seattle citizen group has been planting redwoods far north of their home, an effort regional foresters criticised in 2023.
Nursery methods raise another question. A genetic study found extra chromosomes common in second-growth trees, while plants propagated vegetatively, as in tissue culture, often lose chromosomes, casting doubt on their long-term viability for reforestation.
Source: Sequoia sempervirens
