Developmental evidence for the derivation of syncephalia in Lagascea (Heliantheae; Asteraceae)

The theme of condensation of inflorescences, often accompanied by reduction, is widespread throughout the Asteraceae. Many examples of condensation of the primary Asteraceae inflorescence into secondary aggregations have long been noted. Descriptions of tertiary condensation of inflorescences (i.e., condensation of secondary aggregations) are rarer; partially due to the difficulty of unequivocal documentation. Comparative investigations with the scanning electron microscope yield clear evidence of inflorescence condensation. Developmental stages demonstrating tertiary condensation heads characterize Lagascea helianthifolia, L. aurea, L. palmeri, and L. rigida. Dissections of L. decipiens and L. heteropappus also suggested tertiary condensation. Added to a previous account of the tertiary condensation of L. mollis, seven of the eight species of the genus have been examined and have been found to display tertiary condensation, accompanied by a reduction of the primary inflorescence to single flowers. The most parsimonious explanation would suggest that the tertiarily aggregated inflorescences found in the genus Lagascea evolved only once in that lineage.