Aextoxicaceae Engl. & Gilg — Olivillo Family

Family Overview

Aextoxicaceae Engl. & Gilg, the Olivillo Family, is one of the smallest and most evolutionarily isolated families of flowering plants. It contains a single genus, Aextoxicon, and a single accepted species, Aextoxicon punctatum, an evergreen tree native to central and southern Chile and southwestern Argentina. The family belongs to Berberidopsidales, a small order of superasterids in which Aextoxicaceae is sister to Berberidopsidaceae (Menegoz et al. 2024; APG V 2026).

Aextoxicaceae was formally established by Engler and Gilg in 1920, and its name is conserved. Recognition of the family reflects the long-recognized distinctiveness of Aextoxicon, although understanding its broader affinities proved difficult. The genus was historically associated with a wide range of otherwise disparate families before molecular phylogenetics established its relationship with Berberidopsidaceae. Modern nuclear and chloroplast analyses strongly support Berberidopsidales as a coherent lineage containing these two families (Carlquist 2003; Menegoz et al. 2024).

The relationship is striking because the families look very different at first glance. Aextoxicon is a substantial evergreen forest tree, whereas Berberidopsidaceae consists of woody climbing or scrambling plants in Berberidopsis and Streptothamnus. Wood anatomy nevertheless supplies structural evidence compatible with their relationship. Carlquist (2003) documented numerous shared features, including long vessel elements, scalariform to transitional vessel pitting, tracheids, heterogeneous rays, and extensive pit-membrane remnants in vessel perforations. These similarities complement the much stronger evidence now supplied by molecular phylogenetics.

Floral development has made Aextoxicaceae particularly interesting in studies of angiosperm evolution. Aextoxicon is dioecious, but its unisexual flowers arise through late abortion of organs of the opposite sex rather than beginning development as strictly male or female structures. The flowers are enclosed by a calyptra produced through fusion of two bracteoles. Sepals, petals, and stamens vary somewhat in number and are initiated largely in a spiral sequence, while the gynoecium develops from a single carpel. Ronse De Craene & Stuppy (2010) interpreted this combination of characters in the context of early core-eudicot floral evolution. Modern phylogenomic classifications more specifically place Berberidopsidales among the superasterids, but the unusual developmental morphology remains important for understanding the evolution of floral organization in this part of the angiosperm tree.

The most recent Angiosperm Phylogeny Group classification reinforces the value of retaining Aextoxicaceae as a separate family. APG V continues to recognize both Aextoxicaceae and Berberidopsidaceae and specifically identifies them among several small sister-family pairs for which merger has been considered. Although their relationship is secure, sufficiently convincing shared diagnostic characters have not been demonstrated to make combination preferable, and the two families remain separately recognized pending deeper developmental and genomic study (APG V 2026). Tree TSAR follows that treatment.

Within its present circumscription, the Olivillo Family is characterized by evergreen woody plants with simple leathery leaves, conspicuous peltate scales on young vegetative surfaces, dioecious reproduction, small flowers with distinctive developmental organization, and one-seeded olive-like fruits.

Horticultural and Agricultural Uses

Aextoxicon punctatum is grown outside South America primarily as a botanical-collection tree. It entered cultivation in Britain during the early twentieth century and remains uncommon, although wild-origin material is represented in botanic gardens and arboreta in the British Isles, continental Europe, and western North America. Its principal ornamental qualities are its dense evergreen crown, leathery foliage, pale to metallic-looking leaf undersides, and rusty or silvery peltate scales on young growth. Cool, humid, oceanic climates most closely resemble the conditions under which the tree is naturally successful (O’Brien 2012).

The family also has a history of timber use in Chile. Olivillo wood has been employed for construction, furniture, interior carpentry, and fuel, and historical cutting contributed to the decline of some coastal forests. It is not now an internationally important timber resource.

From a conservation-horticultural perspective, Aextoxicaceae presents an additional complication: recent experimental work indicates that seeds of A. punctatum are sensitive to desiccation. Conventional seed banking therefore has limited value for preserving the lineage, increasing the importance of properly managed living collections, fresh or moist-handled seed, and complementary ex situ techniques (Fernández et al. 2026).

Conservation Issues

The Olivillo Family is not currently considered globally threatened. Aextoxicon punctatum is assessed as Least Concern on the IUCN Red List, reflecting extensive populations remaining through much of southern Chile and adjoining Argentina. Because the species represents the entire family, however, its long-term persistence also preserves a uniquely isolated branch of flowering-plant diversity (Barstow et al. 2018).

Global status obscures strong geographic differences. Chile classifies populations from the Metropolitan Region northward as Vulnerable while treating populations from the O’Higgins Region southward as Least Concern. At the northern end of the range, olivillo survives in isolated coastal ravines and fog-dependent forest islands separated by extensive Mediterranean and semiarid vegetation. These remnants are threatened by habitat conversion, water extraction, development, fire, forest fragmentation, and increasingly severe drought (Ministerio del Medio Ambiente de Chile 2026).

Their importance is greater than their small area suggests. Genetic evidence indicates that the northern semiarid populations, including Fray Jorge and Santa Inés, are long-isolated components of the species’ evolutionary history rather than recent offshoots of the extensive southern forests. Conserving only the large southern populations would therefore fail to preserve the full geographic and genetic diversity of Aextoxicaceae (Núñez-Ávila & Armesto 2006).

Accepted Genera

Accepted genera of Aextoxicaceae

Aextoxicon	Ruiz & Pav. (1794)	Olivillo

Additional Information

Plants of the World Online (opens in a new tab): Current accepted family, genus, and species backbone.
International Plant Names Index (opens in a new tab): Nomenclatural records for Aextoxicaceae and Aextoxicon.
iNaturalist (opens in a new tab): Observation-based records for Aextoxicon punctatum.
Chile SIMBIO (opens in a new tab): Distribution, habitat, threats, protected areas, and Chilean conservation classification.
IUCN Red List (opens in a new tab): Global conservation assessment for Aextoxicon punctatum.

References and Further Reading

APG V (2026) Large-scale nuclear and plastid phylogenomic analyses inform an updated Angiosperm Phylogeny Group classification: APG V. Journal of Systematics and Evolution. https://doi.org/10.1111/jse.70096 (opens in a new tab).

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).

Fernández A, Araya L, León-Lobos P & Contreras S (2026) Seed recalcitrance and its predictability in native and endemic tree species of Chile. Seed Science Research 35(4): 209–220. https://doi.org/10.1017/S0960258526100087 (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) Aextoxicaceae Engl. & Gilg. Plants of the World Online.