Inflorescence evolution in Santalales: integrating morphological characters and molecular phylogenetics

Area of Science:

• Plant morphology and evolution
• Angiosperm phylogeny
• Systematic botany

Background:

• The sandalwood order (Santalales) displays a wide range of inflorescence structures, some unique among flowering plants.
• This diversity poses challenges for morphological interpretation and offers opportunities to study evolutionary patterns.

Purpose of the Study:

• To investigate the evolutionary history of inflorescences within the Santalales using modern phylogenetic methods.
• To test hypotheses regarding the ancestral state of inflorescence characters in the sandalwood order.

Main Methods:

• Phylogenetic analyses were performed using two nuclear and three chloroplast genes from representatives of 146 Santalales genera.
• A character matrix focusing on nine inflorescence traits, including a
• trios
• (groupings of three flowers), was analyzed.
• Bayesian inference with BayesTraits was employed to optimize the
• trios
• character on the phylogenetic tree.

Main Results:

• Phylogenetic analyses resolved 18 major clades within Santalales with strong support.
• The
• trios
• character was not ancestral for the entire order (node A) or for the Opiliaceae, Santalaceae s.l., and Viscaceae clade (node C).
• The
• trios
• character was supported for the Loranthaceae clade (node B), where it represents a triad inflorescence.

Conclusions:

• The dichasium, a specific partial inflorescence, is rare in Santalales and not plesiomorphic for the order.
• Inflorescence diversity in Santalales includes fascicles, cymes, racemose, and compound types, with some families exhibiting highly derived or difficult-to-classify structures.
• The study clarifies the evolutionary significance of specific inflorescence types within the sandalwood order.