Round-leaved Thoroughwax

Bupleurum rotundifolium is an annual herb in the carrot family (Apiaceae), distinguished by its glaucous, perfoliate leaves that appear to be pierced by the stem, giving the plant a distinctive rounded, disc-like foliage silhouette. It produces small yellow flowers arranged in compound umbels typical of the family, attracting small pollinating insects, and it completes its life cycle within a single growing season, relying entirely on seed production for persistence from year to year.

Historically an arable weed, this species is closely tied to traditional cereal cultivation across Europe, western Asia, and North Africa, occurring in disturbed, open terrestrial habitats such as cornfields, field margins, and fallow ground. Its documented range extends from the United Kingdom and Scandinavia through central Europe, the Mediterranean, the Caucasus, and into parts of Iran and Central Asia, with additional occurrences reported outside its native range.

Its decline is driven by modern agricultural intensification, particularly the widespread use of herbicides that eliminate arable weed communities, along with the abandonment of low-intensity traditional farming practices that once allowed it to persist alongside crops. Habitat fragmentation across agricultural landscapes, competition from more aggressive invasive plants, and shifting climatic conditions affecting seed germination timing further compress suitable habitat and reproductive success.

Conservation responses include seed banking, monitoring of remaining populations, and agri-environment schemes in some countries that support arable plant conservation through reduced herbicide use and field margin management. No comprehensive population figures are available, and the population trend is currently listed as unknown. Given the continued dominance of intensive farming methods across its range, the species' long-term outlook remains precarious without sustained, targeted intervention.

Throw-wax occurs in disturbed agricultural soils, particularly cereal fields, field margins, and other cultivated areas with calcareous or clay-rich soils. The species thrives in traditional extensive farming systems with crop rotation and requires open, sunny conditions with minimal competition from other vegetation.