Three species (Aconitum taipeicum, Delphinium giraldii, and Consolida ajacis) of the tribe Delphinieae (Ranunculaceae) were examined using scanning electron microscopy and histological methods. The results showed that members of Delphinieae differ from their polysymmetrical relatives by four unique features: (1) a spiral phyllotaxis of their perianth and stamens, and a series of carpels, which initiated superficially in a whorl-liked arrangement; (2) sepal 2 being the largest one among the five sepals and becoming helmet-shaped or having a spur; (3) petals 2 and 5 initiated adaxially of sepal 2 and also becoming spurred; and (4) the monosymmetry of the first flower becoming established when sepal 2 becomes the largest. Major differences among the species include the timing of development of the second series; the fusion of two petals into a single one in C. ajacis; and, during early developmental stages, the two young spurred petals giving rise to a stalk and two bulges in A. taipeicum, a single bulge in D. giraldii, or an arch blade in C. ajacis. The unequal growth of the perianth, together with the reduction and the rearrangement of the carpels, are critical in inducing the symmetrical transformation of the flowers.
Keywords: Aconitum; Consolida; Delphinieae; Delphinium; Ranunculaceae; floral organogenesis; monosymmetry.