The most endangered tree in the contiguous United States is most likely a battered old oak hidden deep in a Texas mountain range. Its trunk is scarred by a wildfire. Its limbs are weak from a fungal infection. Its habitat is imperiled by climate change. Scientists only realized the species still existed after stumbling upon the ailing specimen during an expedition this spring. And without swift action, researchers warn, quercus tardifolia could truly disappear.

The species is among some 100 US trees staring down the barrel of extinction, according to a sweeping new assessment published Tuesday in the journal Plants People Planet.

Amid an onslaught of invasive insects, a surge in deadly diseases, and the all-encompassing peril of climate change, as many as 1 in 6 trees native to the lower 48 states is in danger of being wiped out, the scientists say. The threatened list includes soaring coast redwoods, capacious American chestnuts, elegant black ash, and gnarled whitebark pine. Yet only eight tree species are federally recognized as endangered or threatened.

“It’s easy to feel that gloom and doom because . . . the scope of the crisis is really, really great right now,’’ said Murphy Westwood, vice president for science and conservation at Morton Arboretum in Illinois and an author of the study. “We’re losing species before they even get described.’’

The new study is the first to list and assess the health of all 881 tree species native to the contiguous United States — an achievement in and of itself, Westwood said, because conservation research rarely focuses on plants. “Plant blindness’’ — the human tendency to overlook the plants that surround us — means that fewer resources are devoted to the organisms that supply Earth’s oxygen, feed its animals, and store more carbon than humanity will emit in 10 years. Until several years ago, scientists didn’t even know how many tree species existed (the number is 58,497).

“It’s this big swath of life that’s totally unstudied or understudied,’’ Westwood said.

Now, a coalition of scientists lead by Botanic Gardens Conservation International is attempting to determine how many of those species are at risk of dying out. Westwood helped lead the US effort. She found, more than two-thirds of species had never been assessed for their extinction risk. Others hadn’t been examined in decades. After five years poring over scientific journals, combing through academic databases, and interviewing experts, the researchers uncovered that swaths of America’s forests have silently slipped toward oblivion.

In the rosaceae family — a diverse group that includes apple trees — more than a quarter of species are considered threatened, endangered, or critically endangered. Half of all ash species are jeopardized by the invasive emerald ash borer, a jewel-green insect whose larvae feed on the tissue just beneath a tree’s bark. An emerging disease known as “laurel wilt’’ is attacking all three native members of the genus persea, imperiling the small, fragrant evergreen trees.

The threats to trees are especially worrying, Westwood said, because of the distinct role they play in nature. They constitute the framework of ecosystems and provide habitat for other creatures. And trees have an essential role in humanity’s efforts to avert catastrophic climate change. The United States’ plan to halve emissions by the end of the decade depends on forests to offset about 12 percent of its planet-warming pollution.