The knotweed family: why these swollen-jointed plants are both culinary staples and notorious weeds.

Gardening · Published 3 October 2026 Swipe more like this →

In short: From the buckwheat in your pantry to the invasive knotweed in your garden, the Polygonaceae family is a botanical powerhouse. Named for their distinctively swollen nodes, these plants have evolved into a diverse group of 1,200 species that shape ecosystems and human diets across the globe.

The name Polygonaceae, first introduced by Antoine Laurent de Jussieu in 1789, likely stems from the Greek words for 'many' and 'knee' or 'joint,' a nod to the prominent, swollen nodes found on the stems of many species. This family is characterized by simple, alternate leaves, often featuring a unique sheathing structure called an ochrea. While most are perennial herbs, the family also encompasses shrubs, vines, and even trees, demonstrating remarkable morphological flexibility.

Taxonomically, the family is well-defined and universally recognized, sitting within the order Caryophyllales. However, its internal structure has been in flux. In 1993, John Brandbyge provided a comprehensive revision, but subsequent DNA-based phylogenetic studies have forced significant reclassifications. Genera such as Coccoloba and Triplaris were shifted between subfamilies, and others, like Symmeria, remain outliers that do not fit neatly into established groupings. As of October 2025, Plants of the World Online recognizes 57 distinct genera.

The family’s impact on human life is profound and contradictory. It provides essential food sources: rhubarb petioles, common sorrel leaves, sea grape fruit, and buckwheat seeds are all staples. Yet, the family is equally famous for its aggressive members, including Japanese knotweed and various species of Persicaria and Rumex, which rank among the world’s most prolific weeds. Whether they are being cultivated for their ornamental value or managed as invasive threats, the Polygonaceae remain a central, if complex, fixture of the botanical world.

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