Phylogeny of Pyroloideae (Ericaceae)

      Pyroloideae are a small subfamily of Ericaceae comprising 4 genera of temperate subshrubs.  Their relationships to the leafless monotropoids are still unclear, but it may well be that the latter were derived from pyroloid ancestors, rendering Pyroloideae paraphyletic.  Even within pyroloids there are trends toward leaflessness, particularly in the P. chlorantha group, where individuals of P. chlorantha are sometimes encountered that have few, small leaves.  Pyrola aphylla is also a member of this group -- this species is leafless or nearly so.

      Of the four genera, Orthilia and Moneses are monotypic.  Chimaphila comprises approximately 6 species and Pyrola has nearly 40.  I have worked out the relationships among these genera based on nuclear ribosomal ITS sequences (see Systematic Botany 24: 398-408, 1999).  The cladogram is shown below, with branch lengths on top of the branches and jackknife values below.  Enkianthus was used as the outgroup.

      Contrary to what might have been expected from previous classifications, P. minor, with its straight style, is not transitional between the remainder of Pyrola (all of which have a curved style) and the rest of the genera (all of which have a straight style -- see illustration at left).  In fact, the straight style is not plesiomorphic in P. minor, but is rather a secondary development.  Given that the development of the small flowers in this species is truncated relative to other Pyrola and that P. minor is embedded within Pyrola, as sister to P. elliptica, I conclude that the straight style in P. minor is a result of paedomorphosis, since all other species have a straight style early in development as well.

      Moneses and Chimaphila form a clade, as do Orthilia and Pyrola.  ITS does not provide enough variation to resolve relationships within each of the these genera satisfactorily.  Hence, we are seeking additional molecular characters to increase resolution in the tree.  We also plan to add additional species of Chimaphila and Pyrola to gain a better understanding of morphological and geographic patterns in these genera.