Evolutionary origin of the Asteraceae capitulum: insights from Calyceraceae

POZNER, R.; ZANOTTI, C.; JOHNSON, L.

Bariloche, Argentina

Congreso; Southern Connection Congress; 2010

CONICET, INTA, Universidad Nacional del Comahue

The Menyanthaceae+Goodeniaceae+Calyceraceae+Asteraceae clade is well supported by molecular and morphological data, with Calyceraceae the sister group of Asteraceae. The two basal families share a basic monotelic thyrse-panicle inflorescence structure, which is not evidently connected with the typical capitulum of Asteraceae that is widely interpreted as a polytelic, condensed inflorescence. The structure of Calyceraceae inflorescences is poorly understood, yet such understanding may show how the Asteraceae capitulum evolved from monotelic inflorescences. We used SEM to study the development and structure of the inflorescence of 8 species of Calyceraceae and found their basic  inflorescence structure is a cephaloid. This structure is like a pauperized panicle with undeveloped internodes, and connects the panicle-thyrse inflorescence of Menyanthaceae and Goodeniaceae with the capitulum of the Asteraceae through 2 morphological  changes: reduction of the first order branches, and loss of the terminal flower. We optimized inflorescence characters on a set of trees derived from ITS sequences thatwere rooted with Dampiera (Goodeniaceae) and included two Asteraceae taxa. Results suggested that simple cephalodia (Boopis, Acicarpha) and true capitula of Asteracae could have appeared as early as the ancestor of the Goodenianceae (Calyceraceae+Asteraceae) clade, while complex cephalodia observed in the remaining Calyceraceae genera are reversions towards richer, condensed panicles.