Aextoxicon Ruiz & Pav. — Olivillo

Treatment and Overview

Olivillo (Aextoxicon Ruiz & Pav.) is a genus of evergreen trees in the Olivillo Family, Aextoxicaceae. It contains a single accepted species, Aextoxicon punctatum, native to central and southern Chile and southwestern Argentina. Mature olivillos can become substantial canopy trees in humid temperate forest, although individuals growing under less favorable conditions may remain much smaller. The genus is readily recognized by its leathery evergreen leaves, conspicuously pale undersides, dense rusty to silvery peltate scales on young growth, and dark olive-like fruits (O’Brien 2012; Royal Botanic Gardens, Kew 2026).

Ruiz and Pavón established Aextoxicon in 1794 in the Florae Peruvianae et Chilensis Prodromus. Its generic limits have proved remarkably stable: no additional living species are currently accepted. Its higher-level placement was far less straightforward. Over the course of its taxonomic history, Aextoxicon was compared or associated with families including Aquifoliaceae, Celastraceae, Elaeagnaceae, Euphorbiaceae, and Icacinaceae, reflecting a combination of unusual characters that provided few obvious clues to its nearest relatives.

Molecular phylogenetics ultimately resolved the genus as the sole member of Aextoxicaceae within Berberidopsidales. Nuclear and chloroplast evidence places Aextoxicaceae as sister to Berberidopsidaceae, whose living genera Berberidopsis and Streptothamnus are woody climbers or scrambling plants rather than canopy trees. The relationship is nevertheless strongly supported, and comparative wood anatomy provides additional structural evidence compatible with the molecular result (Carlquist 2003; Menegoz et al. 2024).

The flowers help explain why Aextoxicon long attracted systematic interest. The genus is dioecious, with male and female flowers borne on separate trees. Floral development shows that unisexuality results from late abortion of the organs of the opposite sex. Two bracteoles fuse into a calyptra enclosing the developing flower, and the sepals, petals, and stamens vary somewhat in number and develop largely in spiral succession. A single carpel forms the gynoecium. This unusual combination of characters has made Aextoxicon useful in comparative studies of floral development and core-eudicot evolution (Ronse De Craene & Stuppy 2010).

The living genus should not be confused with the fossil wood genus Aextoxicoxylon. Fossil woods assigned to Aextoxicoxylon have been described from southern South America, including Upper Cretaceous material from Patagonia. Their name reflects anatomical comparison with Aextoxicon, but Aextoxicoxylon is a separately defined fossil genus. Its species are not extinct species of Aextoxicon and should not be included in the accepted species count of the living genus (Vera et al. 2020).

Horticultural and Agricultural Uses

Aextoxicon remains primarily a tree for specialist botanical collections outside its native range. Olivillo was introduced into British cultivation in the late 1920s and has remained uncommon, although subsequent wild-origin collections broadened its representation in arboreta and botanic gardens. Established plants are cultivated in the British Isles, continental Europe, and western North America (O’Brien 2012).

Its ornamental appeal is subtle but distinctive. Dense evergreen foliage gives established trees a substantial year-round presence, while the peltate scales covering young leaves and shoots can produce a silvery or metallic appearance. The small yellowish flowers are much less conspicuous. Because the genus is dioecious, a collection must contain both male and female plants if fruit and sexually produced seed are desired.

The genus is best suited to cool, humid climates with dependable moisture. Its native distribution strongly favors oceanic and temperate-rainforest environments, making maritime regions better analogues than hot continental climates. Olivillo has historically also supplied timber for furniture, interior carpentry, construction, and fuel in Chile, although it is not now a major commercial timber genus (O’Brien 2012; Ministerio del Medio Ambiente de Chile 2026).

Conservation Issues

The conservation future of Aextoxicon is dependant upon its sole species. A. punctatum remains globally assessed as Least Concern because extensive forests persist through much of southern Chile and adjoining Argentina. Consequently, the genus is not presently close to global extinction (Barstow et al. 2018).

Its range is nevertheless strongly heterogeneous. Northern populations survive as isolated remnants in humid coastal refugia and fog forests embedded within otherwise much drier landscapes. Chile classifies populations from the Metropolitan Region northward as Vulnerable, while populations from the O’Higgins Region southward are considered Least Concern. Genetic work indicates that several of the northern populations represent long-isolated components of the lineage rather than recently fragmented pieces of the southern forests (Núñez-Ávila & Armesto 2006; Ministerio del Medio Ambiente de Chile 2026).

This geographic structure matters unusually strongly in a monotypic genus. Protecting abundant southern populations maintains Aextoxicon as a living genus, but conserving its full evolutionary variation also requires protection of the small and genetically differentiated northern refugial populations.

Accepted Taxa

Accepted taxa of Aextoxicon

Aextoxicon punctatum	Ruiz & Pav.	Andean olivillo

Additional Information

iNaturalist (opens in a new tab): Observations and distribution records for Aextoxicon.
Trees and Shrubs Online (opens in a new tab): Dendrology, cultivation history, and horticultural information.
Plants of the World Online (opens in a new tab): Current accepted genus and species treatment.
International Plant Names Index (opens in a new tab): Original publication and nomenclatural record for Aextoxicon.

References and Further Reading

Barstow M, Beech E & Rivers MC (2018) Aextoxicon punctatum. The IUCN Red List of Threatened Species 2018: e.T34616A124554755. https://doi.org/10.2305/IUCN.UK.2018-2.RLTS.T34616A124554755.en (opens in a new tab).

Carlquist S (2003) Wood anatomy of Aextoxicaceae and Berberidopsidaceae is compatible with their inclusion in Berberidopsidales. Systematic Botany 28(2): 317–325. https://doi.org/10.1043/0363-6445-28.2.317 (opens in a new tab).

Menegoz K, Villarroel AE & Lavandero N (2024) Phylogeny of Berberidopsidales based on nuclear and chloroplast loci, with the description of a new species of Berberidopsis endemic to Central Chile. Taxon 73: 800–817. https://doi.org/10.1002/tax.13170 (opens in a new tab).

Ministerio del Medio Ambiente de Chile (2026) Ficha de especie: Aextoxicon punctatum (Ruiz & Pav.). Sistema de Información de la Biodiversidad, Chile.

Núñez-Ávila MC & Armesto JJ (2006) Relict islands of the temperate rainforest tree Aextoxicon punctatum (Aextoxicaceae) in semi-arid Chile: Genetic diversity and biogeographic history. Australian Journal of Botany 54: 733–743. https://doi.org/10.1071/BT06022 (opens in a new tab).

O’Brien S (2012) 737. Aextoxicon punctatum. Curtis’s Botanical Magazine 29: 182–193. https://doi.org/10.1111/j.1467-8748.2012.01784.x (opens in a new tab).

Ronse De Craene LP & Stuppy W (2010) Floral development and anatomy of Aextoxicon punctatum (Aextoxicaceae-Berberidopsidales): An enigmatic tree at the base of core eudicots. International Journal of Plant Sciences 171(3): 244–257. https://doi.org/10.1086/650161 (opens in a new tab).

Royal Botanic Gardens, Kew (2026) Aextoxicon Ruiz & Pav. Plants of the World Online.

Vera EI, Perez Loinaze VS, Llorens M & Passalia MG (2020) The fossil genus Aextoxicoxylon (Magnoliopsida) in the Upper Cretaceous Puntudo Chico Formation, Chubut Province, Argentina. Cretaceous Research 107: 104315. https://doi.org/10.1016/j.cretres.2019.104315 (opens in a new tab).