The genus Delphinium, comprising some 300 species, is distributed throughout the temperate regions of the northern hemisphere, ranging from the Mediterranean basin to Japan, Siberia, and North America. A few species even occur on tropical African mountains. The centre of Delphinium species diversity is southwest China and the eastern Himalayas where some 150 species are found. The genus apparently expanded into North America about three million years ago.
Across Delphinium there is a diversity of habit and life history. Alpine species may be a little as 10 cm tall, whilst meadow species may be more than 2 m tall. Some species are annuals, whilst others are biennials and perennials. Short-lived members of the genus tend to be found in xeric or Mediterranean climates, whilst perennial species are associated with cold, wet, high altitude habitats in Asia, North America and Africa. Chinese Delphinium species diversification is associated with the evolution of perennial life histories.
Evolutionary histories based on DNA sequence data are changing our concept of Delphinium. Researchers have suggested the genus should include the larkspurs (Consolida) but exclude a small number of species closely related to stavesacre (Delphinium staphyisagria). The latter species would be included in a new genus.
The name Delphinium is derived from the Greek meaning 'dolphin'; the nectary spur of the insect-pollinated flowers is thought to resemble the mammal. The spur is an extension of one of the flower's brightly-coloured sepals; the petals are inconspicuous compared to the sepals. Delphinium fruits are dry follicles that split along one side to reveal small, black seeds attached to fruit's open edge. The seeds, like the other parts of the plant, are highly toxic; they are rich in diterpenoid alkaloids.
Spikes of delphinium blooms, ranging in colour from white though blue and mauve to pink are familiar garden flowers. Delphinium breeding to satisfy the tastes of gardeners is an important element of the horticultural industry. Many of these cultivated plants are complex cultivars and hybrids, often with the European species Delphinium elatum in their ancestries.
The toxicity of the genus has attracted fringe medical practice. Southern Mediterranean stavesacre, the seeds of which have been used to control pests since the late-eighteenth century, must 'struggle through rock in order to grow and unfold. Likewise, the human personality in need of the remedy Staphysagria feels angered and suppressed, as if having to break or cut through rock in order to live freely'.
Jabbour F and Renner SS 2012. A phylogeny of Delphinieae (Ranunculaceae) shows that Aconitum is nested within Delphinium and that Late Miocene transitions to long life cycles in the Himalayas and Southwest China coincide with bursts in diversification. Molecular Phylogenetics and Evolution 62: 928-942.
Richardson-Boedler C 1999. The Doctrine of Signatures: a historical, philosophical and scientific view (I). British Homeopathic Journal 88: 172-177.