The Earth includes over 60,000 known tree species, but this biodiversity is fragile. While most trees are numerous, many species have been reduced to only a handful of individuals in the wild. This reduction places some trees in a state of functional extinction, making the “rarest” a matter of counting single, remaining specimens.
The World’s Single Rarest Tree
The world’s rarest tree is Pennantia baylisiana, a small evergreen found exclusively on the remote Three Kings Islands of New Zealand. Only one known individual survives in its natural habitat. The sole remaining tree is a mature female specimen clinging to an inaccessible cliff face on Great Island, 55 kilometers northwest of Cape Reinga.
New Zealand botanist Geoff Baylis discovered the tree in 1945. The species was likely decimated by introduced goats, which severely degraded the native vegetation before their eradication in 1946. Because the single wild tree is dioecious (requiring a male plant for reproduction), its ability to produce viable seeds was severely limited.
Conservation efforts began immediately, with cuttings taken from the original tree to propagate the species in cultivation. Decades later, scientists induced a cultivated female clone to produce viable seed through self-pollination. This intervention allowed a small population of P. baylisiana to be established in nurseries and mainland plantings, securing the species’ future outside its original habitat.
How Scientists Define Tree Rarity
Scientists use the IUCN Red List of Threatened Species to classify the rarity and extinction risk of all life forms, including trees. This system employs quantitative criteria to categorize a species into one of nine groups. The most relevant categories for extreme rarity are “Critically Endangered” (CR) and “Extinct in the Wild” (EW).
A species is classified as Critically Endangered when it faces an extremely high risk of extinction in the wild, often based on a small population size or restricted geographic range. This status is applied when the total number of mature individuals is fewer than 50, or if the species is found in an area of occupancy smaller than 10 square kilometers. A population reduction of 80 to 90 percent over the last ten years or three generations can also trigger this status.
The category “Extinct in the Wild” is assigned when a species is known only to survive in cultivation, in captivity, or as a naturalized population outside its historical range. This status is determined after exhaustive surveys of the known and expected habitat fail to record any individuals. These classifications provide a globally accepted language for quantifying the degree of threat, guiding conservation efforts toward the most vulnerable species.
Notable Critically Endangered Species
While Pennantia baylisiana represents rarity as a single wild specimen, other trees are on the brink of extinction. The Encephalartos woodii, a cycad from South Africa, is functionally extinct in the wild. All living specimens are clones descended from a single male plant discovered in 1895; no female has ever been found, making natural reproduction impossible.
Another example is the Tahina spectabilis, commonly known as the Suicide Palm, endemic to a tiny area of northwestern Madagascar. This massive palm is monocarpic, meaning it grows for 30 to 50 years before flowering once and then dying. With fewer than 100 individuals known in the wild, its rarity is compounded by its life cycle and the immediate threats of fire and grazing livestock to its restricted habitat.
The Florida Torreya (Torreya taxifolia) is critically endangered due to a fungal disease that nearly wiped out the population in the 1950s. Once common along the Apalachicola River, the species now primarily exists as small, diseased shrubs, having lost the ability to reach maturity. These examples illustrate how rarity is defined not only by population count but also by the biological and environmental pressures facing a species.