Evolution of morphological traits in Verbenaceae.

Area of Science:

• Botany
• Evolutionary Biology
• Phylogenetics

Background:

• A recent molecular phylogeny proposed a new infrafamilial circumscription of Verbenaceae with eight tribes.
• Two genera, Dipyrena and Rhaphithamnus, remain unplaced within this new classification.
• Traditional classifications relied on morphological characters, whose evolutionary history was unclear.

Purpose of the Study:

• To reconstruct the evolutionary history of morphological characters used in Verbenaceae classification.
• To investigate the evolutionary significance of these traits, particularly within the Verbeneae and Lantaneae tribes.
• To assess the utility of morphological traits in light of recent molecular phylogenetic findings.

Main Methods:

• Optimization of 21 morphological and cytological characters onto a molecular phylogeny of Verbenaceae.
• Characters analyzed included habit, vegetative and floral morphology, ovary and fruit characteristics, and chromosome number.

Main Results:

• Most tribes are supported by at least one morphological trait, with exceptions for Duranteae and Citharexyleae.
• Specific synapomorphies were identified for Verbeneae (suffrutescent habit, sessile flowers), Lantaneae (short style, entire stigma), Neospartoneae (sessile flowers, unicarpellate ovaries), Priveae (suffrutescent habit), Casselieae (homothetic pleiobotrya, absent adaxial staminode), and Petreeae (undivided fleshy fruits).
• Putative plesiomorphies for the Verbenaceae ancestor were discussed.

Conclusions:

• Many traditional classification characters are highly homoplastic, limiting their reliability in defining relationships within Verbenaceae.
• Traditional assumptions about character evolution and polarity were found to be incorrect in some instances.
• Morphological data, when optimized onto a molecular phylogeny, can illuminate evolutionary patterns but also highlight the limitations of morphology-based classification.