Quercus Tardifolia, commonly known as the lateleaf oak or Chisos Mountains oak, is an exceptionally rare, potentially critically endangered evergreen tree restricted to high-elevation montane ecosystems. It typically grows as a small tree or clumped shrub, reaching up to 10 meters in height, and is characterized by furrowed gray bark and dark reddish-brown, densely pubescent twigs that measure 1.5 to 2.5 mm in diameter. Its terminal buds are brown or reddish-brown, ovoid to ellipsoid, and display ciliate-margined scales with hairy apices. The species derives its common and scientific names from its distinct phenological habit of leafing out significantly later in the spring than comparable oak species sharing its range. Its thick, planar leaves are broadly elliptic or obovate, measuring 5 to 10 cm long by 2 to 7 cm wide, and feature a cordate or rounded base and an acute to obtuse apex. The leaf margins are structured with 3 to 4 shallow lobes per side, bearing a total of 6 to 12 awns. The upper leaf surface is a dull green and somewhat rugose (wrinkled), while the lower surface is covered in a highly conspicuous, velvety layer of woolly, yellowish tomentum. The reproductive structures of Quercus tardifolia remain incompletely documented; it produces biennial acorns that develop in pairs, though fully mature acorns have not been formally characterized or collected due to the tree’s infrequent and irregular reproductive cycles. Ecologically, the lateleaf oak is strictly limited to moist, sheltered arroyos, canyon bottoms, and mixed pine-oak-juniper woodlands at elevations around 2,000 to 2,100 meters, thriving primarily in soils derived from igneous rock formations. Its global distribution is famously confined to a microscopic footprint within the Chisos Mountains of Big Bend National Park in West Texas, with unconfirmed, historically reported sightings in the adjacent Sierra del Carmen range of Coahuila, Mexico. Regarded as one of the rarest trees in the world, the species was widely feared extinct after the last known individual died in 2011, until a single, fire-scarred living specimen was rediscovered in Boot Canyon in 2022. Because oaks cannot be traditionally seed-banked, this lone individual is the focus of intense preservation efforts, including grafting and intensive field monitoring, while ongoing taxonomic research seeks to determine whether the tree represents a distinct relict line or a rare hybrid between Quercus gravesii and Quercus hypoxantha.