Agonis is a genus of flowering shrubs and trees in the family Myrtaceae (order Myrtales), comprising around ten species all endemic to the south-western coast of Western Australia. The genus was first formally described in 1828 by Augustin Pyramus de Candolle as a section of Leptospermum in his Prodromus Systematis Naturalis Regni Vegetabilis, then elevated to full genus rank in 1830 by Robert Sweet in Hortus Britannicus.
Plants in the genus are recognisable by their simple leaves dotted with small oil glands, and by clusters of bisexual flowers borne in heads along the leaf axils. Each flower has a leathery floral tube, five egg-shaped or triangular sepals, five white petals, and 15 to 30 stamens arranged in a single whorl — six or seven of which are positioned opposite the sepals with none opposite the petals. The ovary is inferior, with the style seated in a depression at its apex. Fruits are woody capsules containing winged seeds.
The most widely known member is Agonis flexuosa (Willd.) Sweet, the Western Australian peppermint or willow myrtle, a weeping tree valued in horticulture and street planting for its graceful, pendulous branches and peppermint-scented foliage. Other accepted species include A. grandiflora, A. theiformis, A. undulata, and A. baxteri.
Etymology
The genus name Agonis derives from the Greek agon (a gathering or assembly), referring to the flowers clustered together in heads along the leaf axils.
Distribution
All species of Agonis are endemic to Western Australia, restricted to the south-western coastal region. This area falls within the Southwest Australian Floristic Region, one of the world's biodiversity hotspots.
Taxonomy Notes
Agonis was originally described by Augustin Pyramus de Candolle in 1828 as Leptospermum sect. Agonis in the Prodromus Systematis Naturalis Regni Vegetabilis. Robert Sweet raised it to genus rank in 1830 in Hortus Britannicus, giving the accepted authorship (DC.) Sweet. The genus belongs to the family Myrtaceae, order Myrtales. Around ten species are currently recognised in the GBIF backbone.
