The plant genus whose larkspur species contain toxic diterpenoid alkaloids is Delphinium.
Delphinium belongs to the buttercup family, Ranunculaceae, and contains roughly 300 annual and perennial species native mainly across the Northern Hemisphere. Its flowers commonly have a distinctive backward-pointing spur, which helped inspire the common name larkspur. The genus name comes from the Ancient Greek word for “dolphin,” likely referring to the flower’s shape.
All parts of Delphinium are considered poisonous, with younger growth often especially hazardous. Its diterpenoid alkaloids include methyllycaconitine and related compounds that can disrupt neuromuscular signaling. In livestock, poisoning may produce weakness, paralysis, breathing failure and death, with cattle particularly vulnerable on western North American rangelands.
The main trap is the option Aconitum: it is a close relative in the same family and also contains dangerous diterpenoid alkaloids, but larkspur refers to Delphinium. Annual larkspur species may also be placed in Consolida in some classifications, although molecular studies have treated Consolida as embedded within Delphinium.