DEVELOPMENTAL EVIDENCE FOR THE DERIVATION OF SYNCEPHALIA IN LAGASCEA (HELIANTHEAE, ASTERACEAE)

The theme of condensation of inflorescences, often accompanied by redu ction, is widespread throughout the Asteraceae. Many examples of conde nsation of the primary Asteraceae inflorescence into secondary aggrega tions have long been noted. Descriptions of tertiary condensation of i nflorescences (i.e., condensation of secondary aggregations) are rarer ; partially due to the difficulty of unequivocal documentation. Compar ative investigations with the scanning electron microscope yield clear evidence of inflorescence condensation. Developmental stages demonstr ating 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 prev ious account of the tertiary condensation of L. mollis, seven of the e ight species of the genus have been examined and have been found to di splay tertiary condensation, accompanied by a reduction of the primary inflorescence to single flowers. The most parsimonious explanation wo uld suggest that the tertiarily aggregated inflorescences found in the genus Lagascea evolved only once in that lineage.