In 1973, botanist Robin Foster, working in Manu National Park in southeastern Peru, found a small tree with bright orange fruits that resembled paper Chinese lanterns. Having collected samples, he tried to determine the plant's family but could not: the leaves, flowers and fruits seemed to belong to different groups and did not add up to a familiar picture. Foster admitted that for most plants the family can be named at first glance, but this case turned out to be an exception.
Local people of the Matsigenka nation had long known this plant and used it in everyday life. For science, however, the tree remained a mystery for almost half a century. The dried specimens lay in herbaria, the colleagues to whom Foster showed them could not even name the family, and attempts to extract DNA from the dried material led nowhere.
The turning point came when a researcher working in Manu, Patricia Álvarez-Loayza, sent a fresh sample of the plant to the Field Museum in 2015. DNA analysis showed that the tree's closest relatives belong to the family Picramniaceae, although outwardly it hardly resembled its relatives.
The decisive factor was a careful study of the tiny flowers, only 2–3 millimetres long. An expert on this family from the New York Botanical Garden, Wayt Thomas, and his colleagues compared the molecular data with the morphology and concluded that this was a separate genus and species. Thus Aenigmanu alvareziae came into being: the name "Aenigmanu" translates as "the enigma of Manu", and the species name immortalises Álvarez-Loayza, without whom the sample for genetic analysis would not have been obtained. The description was published in the journal Taxon on 6 October 2021, meaning the solution took almost fifty years.
The tree grows to about six metres and grows in the understorey of humid tropical forest. It is found in Peru and in the Brazilian state of Acre. The main problem is its habitat: the species is associated with a rare type of lowland forest that is almost never flooded. Such areas are rapidly shrinking because of logging and climate change, so researchers recommend classifying the species as endangered.
The scientific name matters not only for systematics. The official description secures the species' place in the tree of life and provides a concrete object for protection: it is now possible to specify exactly which areas of forest must be preserved. That is precisely why the authors of the work regard the naming as an important step in protection.
There is also practical interest. The fruits are sweet and creamy in taste, but people should not eat them: the plant will not become a food resource. However, belonging to Picramniaceae opens another direction. British taxonomist Martin Cheek, who was not involved in the work, noted that this family often contains compounds that could be useful in developing anticancer drugs, and it is precisely in this direction that the properties of the new species should now be sought.
The tree's story shows how much unknown remains hidden in tropical forests. Foster himself stresses that plants are poorly studied, especially those of the upper Amazon, and yet they are the foundation of all the region's ecosystems. To understand the changes taking place in the tropics and to protect what remains, one must first know what grows there.
