Monotropsis Schweinitz is a genus of leafless, achlorophyllous, mycoheterotrophic plants in the small Monotropoideae subfamily of the blueberry family, Ericaceae, collectively referred to as the monotropoids. The monotropoids are a monophyletic group, embedded deeply within the Ericaceae, and most closely related to the Arbutoideae. Monotropsis is a less commonly encountered monotropoid. The genus is currently monotypic and occurs in the Appalachian Mountains from West Virginia to Alabama, on the Coastal Plain in Virginia, and as a disjunct in northern Florida.
Four species have been described in the genus, all treated as synonyms of the type species Monotropsis odorata. Monotropsis reynoldsiae, found exclusively in Florida, was distinguished from M. odorata based on flowering period, flower color, and its sepal length to width ratio. Monotropsis lehmaniae was distinguished based on flowering period, sepal color, and sepal length to width ratio. Another genus and species, Cryptophila pudica, was distinguished by fruit type and floral anatomy. All species were placed as synonyms of Monotropsis odorata because of variability in all distinguishing features. This study reevaluated the status of all synonyms of Monotropsis odorata using a holistic approach to species delimitation emphasizing quantitative differences and incorporated four major lines of evidence: phenology, morphology, geography, and DNA.
Phenological, morphological, and geographical differences were assessed by examining over 200 herbarium specimens, supplemented with 16 new collections.
Phenological data shows that Monotropsis lehmaniae does not have a flowering period distinct from that of M. odorata, while M. reynoldsiae does.
The morphological data viewed using Principle Components Analysis, box plots, and scatter plots show Monotropsis reynoldsiae forming a distinct cluster relative to all specimens of Monotropsis odorata. Box plots and scatter plots indicate that the size of many organs differs between the two species they are distinguishable based on these alone.
Anatomical data were collected by making sections of paraffin-embedded flowers. The results support those of the phenological and morphometric data. Monotropsis lehmaniae is immature M. odorata, while M. reynoldsiae is distinguishable by the presence of a substance which stains positively in Safranin in the epidermis.
The geographical evidence supports two units separated by a wide geographic space. One is found in the Appalachians and another in Florida. These units correspond to Monotropsis odorata and M. reynoldsiae, respectively.
Lastly, DNA evidence was gathered using material from the 16 new collections, plus one additional collection. Three loci examined. Two nuclear loci (ITS/26S and Xdh 1296-1869) and one chloroplast locus (rpl32-trnL) were sequenced. These were analyzed separately and together using Maximum Parsimony. Support values using jackknife resampling and branch lengths were plotted onto the strict consensus tree. The results were uninformative (Xdh 1296-1869) or gave two well-supported (greater than 90 percent support) clades (ITS/26S and rpl32-trnL). These clades were supported by a difference of six base pairs and corresponded to Monotropsis odorata or M. reynoldsiae.
All results support the recognition of two species of Monotropsis: M. odorata and M. reynoldsiae. The taxonomic history and ecology of these species is also summarized.