Atraphaxis is a genus of approximately 40 species of flowering shrubs in the family Polygonaceae, order Caryophyllales. The genus was established by Carl Linnaeus in 1753 and belongs to the tribe Polygoneae within the subfamily Polygonoideae, where molecular phylogenetic studies have confirmed it as a distinct clade most closely related to the genera Duma and Polygonum — a grouping sometimes called the "DAP clade."
Species of Atraphaxis are much-branched woody plants that form low shrubs or shrubby tufts. The current season's branchlets are herbaceous and carry the leaves and flowers. Leaves are simple and alternate, with very short stalks that are almost sessile, and the membranous ochreas (sheath-like stipules characteristic of the family) are usually two-veined and more or less joined at the base. Flowers are borne in fascicles of one to three, gathered into raceme-like inflorescences; the tepals are persistent and either form a narrow tube with unequal lobes or are bell-shaped with equal segments. The fruits are wingless achenes.
The generic boundaries of Atraphaxis within Polygonaceae have historically been contested, and some species have at various times been transferred to or from related genera, though modern molecular work supports a coherent circumscription of the genus. Plants of the World Online recognized 41 species as of March 2019.
Taxonomy Notes
Atraphaxis was erected by Carl Linnaeus in 1753. The boundaries between Atraphaxis and related genera within Polygonaceae have long been debated, with species periodically reassigned to and from other genera. Molecular phylogenetic analyses have resolved the genus as a distinct clade within the tribe Polygoneae (subfamily Polygonoideae), most closely allied to Duma and Polygonum in the so-called "DAP clade."
