Fitzroya is a monotypic genus in the cypress family.

The single living species, Fitzroya cupressoides, is a tall, long-lived conifer native to the Andes mountains of southern Chile and Argentina, where it is an important member of the Valdivian temperate rain forests. The scientific name of the genus honours Robert FitzRoy; common names include alerce ("larch", Spanish), lahuán (Spanish, from Mapuche Native American name lawal), and Patagonian Cypress.

F. cupressoides is a very large evergreen tree, the largest tree species in South America, normally growing to 40–60 m (131–196 ft; but occasionally more than 70 m in Argentina) tall and up to 5 m in trunk diameter. Much larger specimens existed in the past before the species was heavily logged in the 19th and 20th centuries; Charles Darwin reported finding a specimen 12.6 m (41' 6") in diameter. The leaves are in decussate whorls of three, 3–6 mm long (to 8 mm long on seedlings) and 2 mm broad, marked with two white stomatal lines. The cones are globose, 6–8 mm diameter, opening flat to 12 mm across, with nine scales in three whorls of three. Only the central whorl of scales is fertile, bearing 2-3 seeds on each scale; the lower and upper whorls are small and sterile. The seeds are 2–3 mm long and flat, with a wing along each side. The seeds mature 6–8 months after pollination.

The largest known living Fitzroya cupressoides is Alerce Milenario in Alerce Costero National Park, Northeren Patagonia, Chile. It is more than 60 m tall, with a trunk diameter of 4.26 m. It is possible that larger trees of this species exist. It is designated as a national monument in Chile.

In 1993 a specimen from Chile was found to be 3,622 years old, making it the second oldest fully verified (by counting growth rings) age for any living tree species, after the Great Basin Bristlecone Pine.

A team of researchers from the University of Tasmania found fossilized foliage of Fitzroya on the Lea River of northwest Tasmania. The 35 million year-old fossil has been given the species name Fitzroya tasmanensis. The finding demonstrates the ancient floristic affinities between Australasia and southern South America, which botanists identify as the Antarctic flora.

Logging of Fitzroya in colonial Chile began in 1599 and continued until 1976 when it became forbidden by law, although illegal logging still occasionally occurs. During the colonial era in Chiloé Fitzroya wood was highly valued and roof shingles of Fitzroya were used as currency called "real de alerce".

Named for Vice-Admiral Robert FitzRoy, RN, who achieved lasting fame as the captain of HMS Beagle during Charles Darwin's famous voyage, and as a pioneering meteorologist who made accurate weather forecasting a reality. He was an able surveyor and hydrographer and served as Governor of New Zealand from 1843 to 1845.