Abstract

PREMISE OF THE STUDY
The sandalwood order (Santalales) includes members that present a diverse array of inflorescence types, some of which are unique among angiosperms. This diversity presents a interpretational challenges but also opportunities to test fundamental concepts in plant morphology. Here we use modern phylogenetic approaches to address the evolution of inflorescences in the sandalwood order.
METHODS
Phylogenetic analyses of two nuclear and three chloroplast genes was conducted on representatives of 146 of the 163 genera in the order. A matrix was constructed that scored nine characters dealing with inflorescences. One character “trios” that encompasses any grouping of three flowers (i.e. both dichasia and triads) was optimized on samples of the posterior distribution of trees from the Bayesian analysis using BayesTraits. Three nodes were examined: the most recent common ancestors of A) all ingroup members, B) Loranthaceae, and C) Opiliaceae, Santalaceae s. lat. and Viscaceae
KEY RESULTS
The phylogenetic analysis resulted in many fully resolved nodes across Santalales with strong support for 18 clades previously named as families. The trios character was not supported for nodes A and C whereas it was supported for node B where this partial inflorescence type is best described as a triad.
CONCLUSIONS
Essentially every major inflorescence type can be found in Santalales, however, the dichasium, a type of partial inflorescence, is rarely seen and is not plesiomorphic for the order. In the family Erythropalaceae, inflorescences are mostly in small, axillary fascicles or cymes. Successive families show both cymose and racemose types as well as compound systems (e.g. thyrses). Inflorescences in Amphorogynaceae and Viscaceae are not dichasial and in general are difficult to compare to “standard” inflorescences.