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Abstract Detail


Developmental and Structural Section

Reinheimer, Renata [1], Zuloaga, Fernando [2], Vegetti, Abelardo C. [3], Pozner, Raul [2].

Inflorescence diversification of the PCK Clade (Poaceae: Panicoideae: Paniceae) and new insight about its phylogeny.

The PCK Clade, represented by at least six genera (Brachiaria, Urochloa, Eriochloa, Megathyrsus, Melinis and Chaetium), is a strong monophyletic group within the Paniceae tribe (Poaceae). Despite the effort made by many authors, the internal resolution of this group remains poorly solved. To better understand of the phylogeny of PCK clade, we analyzed the structure and development of the inflorescence, spikelet and floret of that group, to determine morphological homologies and find new characters to combine with molecular data previously published into an integrated phylogenetic analysis. The most important results are: (1) twenty-one adult inflorescence types were identified, (2) an extensive variation of branch system and spikelet development pattern was found (some of them new for Paniceae and even for the grass family), (3) nine different floral developmental patterns were described and, (4) some results support the possibility of more than one sexual expression pattern. The phylogenetic analysis combining previously published molecular data and our results on inflorescence morphology and development, showed that Brachiaria s.s and Melinis are the Basal Clade, while Urochloa is paraphyletic and associated with Megathyrsus and Eriochloa. Nevertheless, the phylogeny of the PCK Clade remains unsolved. The lack of a phylogenetic signal and the weak resolution of evolutionary relationship among species may be interpreted as a signal of explosive speciation or rapid radiation. Evidences for this hypothesis are: (1) coincidence in the lack of internal resolution and politomies in the consensus trees presented until today, (2) weakness of characters used, alone or combined, to understand the entire history of the group, (3) the wide morphological diversity among species in terms of inflorescence structure and development.


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1 - University of Missouri Saint Louis, Biology, One University Bv., Saint Louis, MO, 63121, USa
2 - Instituto De Botánica Darwinion, Casilla De Correo 22, San Isidro, Buenos Aires, B1642HYD, Argentina
3 - Facultad de Ciencias Agrarias, Catedra: Morfologia Vegetal, Kreder 2805, Esperanza, Santa Fe, S3080HOF, Argentina

Keywords:
inflorescence
morphology
phylogeny
PCK Clade
Grass.

Presentation Type: Oral Paper:Papers for Sections
Session: CP26
Location: Boulevard C/Hilton
Date: Tuesday, July 10th, 2007
Time: 9:00 AM
Number: CP26005
Abstract ID:1645


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