Santalales

Current Phylogenetic Concepts

There have been a number of molecular phylogenetic studies of Santalales by Nickrent and collaborators.  The individual papers can be accessed on his professional web page HERE.  The classification of the entire order Santalales was revised (Nickrent et al. 2010) and that paper can be seen HERE. The most recent molecular phylogenetic study of Santalales is by Su et al. (2015) that can be accessed HERE.  This paper shows that Balanophoraceae in the traditional sense is actually composed of two clades that are recognized therein as families.

Traditional Phylogenetic Concepts

Concepts of relationships in this order date to the 19th. century. Comprehensive treatments in Engler's Die Naturlichen Pflanzenfamilien by various authors (Engler, Hieronymus, Solms-Laubach) provided the framework of relationships that have been, to a greater or lesser degree, followed by many others since. The later edition of Nat. Pflan. (Engler and Harms, 16b), expanded upon the earlier concepts and included treatments by other specialists: Sleumer (Olacaceae and Opiliaceae), Pilger (Santalaceae), Skottsberg (Misodendraceae), Engler & Krause (Loranthaceae), and Harms (Rafflesiaceae, Hydnoraceae, and Balanophoraceae).

One of the first evolutionary "trees" proposed for the order was by Fagerlind (1948) -- see figure below. Some of the relationships have been supported by subsequent work (both morphological and molecular) such as the early branching position of Olacaceae, the recognition of a separate Opiliaceae (apart from Olacaceae), separate familial status for the mistletoe families Loranthaceae and Viscaceae and an evolutionarily advanced position of the latter family in the order. This system also showed the derivation of Balanophoraceae from within Loranthaceae. Fagerlind's classification decisions were strongly influenced by the presence of Allium type embryo sac development type and reductions of the gynoecium in the various groups. Up until the advent of molecular phylogenetics, the presence of the holoparasitic Balanophoraceae within Santalales was interpreted by many (including your author of PPC!) as an example of unrecognized convergent evolution. But compare Fagerlind's position of Balanophoraceae to what is reported in Su et al. (2015).  Fagerlind could have been "right for the wrong reasons", but for now let's give him the benefit of the doubt! 

Major contributions to our understanding of relationships in this order were made by Johri and Bhatnagar (1960), Kuijt (1968, 1969), Wiens and Barlow (1971), and Bhatnagar and Johri (1983). These authors are not in complete agreement as to the exact topology of the families in the order; however, all show Olacaceae as early branching since it contains both parasitic and nonparasitic members.

The following table shows some general evolutionary trends in morphological features seen in the order. Many of these trends have been "explored" by separate lineages, thus giving rise to convergent features.

SIUC / College of Science / Parasitic Plant Connection / Relations: Santalales
URL: http://www.parasiticplants.siu.edu/Relation-Santalales.html
Last updated: 18-Nov-15 / dln