The Systematics of Monotropsis (Ericaceae)

Rose, Jeffrey

Monotropsis Schweinitz is a genus of leafless, achlorophyllous, mycoheterotrophic plants in the subfamily Monotropoideae of the blueberry family, Ericaceae. The Monotropoideae is small, comprised of 14 species and 10 genera, collectively referred to as the monotropoids. The monotropoids are currently viewed as a monophyletic group, embedded deeply within the Ericaceae and most closely related to the woody subfamily Arbutoideae. Monotropsis is one of the more uncommonly encountered monotropoids. The genus in currently monotypic and occurs in mixed woods in the Appalachian Mountains from West Virginia south and west to Alabama, on the Coastal Plain in Virginia, and as a disjunct in northern peninsular Florida. Despite containing only one species as currently circumscribed, 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 several characters including flowering period, flower color, and its sepal length to width ratio. Monotropsis lehmaniae was distinguished based in part on flowering period, sepal color, and its sepal length to width ratio. Another genus and species, Cryptophila pudica, was distinguished by fruit type and internal floral anatomy. All species were placed as synonyms of Monotropsis odorata based on supposed variability or misinterpretation of all distinguishing features. This study reevaluated the status of all synonyms of Monotropsis odorata using a holistic approach to species delimitation emphasizing quantitative differences. The study incorporated four major lines of evidence: phenology, morphology (including anatomy), geography, and DNA. Phenological, morphological, and geographical differences between the described species were assessed by examining over 200 herbarium specimens, supplemented with collections from 16 populations made by the author and others. Phenological data, as measured by the percent of specimens in a particular phenological condition per month of collection, shows that Monotropsis lehmaniae does not have a flowering period distinct from that of M. odorata, while M. reynoldsiae does. The morphological data were scored as quantitative measures. The data as viewed using Principle Components Analysis, box plots, and scatter plots shows Monotropsis reynoldsiae forming a distinct cluster relative to all specimens of Monotropsis odorata. Further, box plots and scatter plots indicate that the absolute size of many organs differs between the two species. Therefore, two species within Monotropsis are distinguishable based on organ size. Anatomical data were collected by making thin sections of paraffin-embedded flowers. Evidence supports the results of the phenological and morphometric data. Monotropsis lehmaniae represents immature individuals ofM. odorata, while M. reynoldsiae is distinguishable based on the presence of an epidermal layer impregnated with a substance which stains positively in Safranin. 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, the DNA data evidence was gathered using material from the 16 collections made by the author, plus one additional collection.... 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.

The Systematics of Monotropsis (Ericaceae)

Collections