The Parmotrema acid test: a look at species delineation in the P. perforatum group 40 y later

Abstract

Parmotrema perforatum and its relatives form a morphologically distinctive group of species, most of which are common and endemic to eastern North America. Species delimitation in this ecologically important group was the subject of extensive inquiry before the advent of molecular systematics and computationally intensive niche modeling. As part of a large-scale lichen biodiversity inventory of the Mid-Atlantic Coastal Plain, we used ITS sequence data to examine the utility of characters (morphological, chemical, reproductive, ecological) in circumscribing four species in this group (P. hypoleucinum, P. hypotropum, P. perforatum, P. subrigidum). We found that P. hypoleucinum and P. subrigidum as currently circumscribed are monophyletic and the latter comprises two chemotypes differing in the presence or absence of norstictic acid in addition to alectoronic acid. The sequences of P. hypotropum and P. perforatum, which are chemically identical species and differ only in reproductive mode, were intermixed in a single, well-supported clade. The two chemotypes of P. subrigidum are partially allopatric and their sequences are >99% identical. Nonetheless, niche modeling suggests they occupy significantly different ecological niches. These results provide a new perspective on much-debated questions on species circumscription in lichens and suggest new avenues for genetic, ecological and systematic research.

• apothecia
• asexual reproduction
• molecular phylogenetics
• soredia

Acknowledgments

The authors were supported by NSF Award DEB-1145511 (to JCL and R.C. Harris). Fieldwork and laboratory work was supported by the same award. We thank the following for providing permission to collect on lands where material used in this study was obtained: Delaware Wild Lands, DE Department of Parks and Recreation, MD Department of Natural Resources, NC Department of Natural Resources, NC Wildlife, PA Department of Conservation and Natural Resources, PA Came Commission, The Nature Conservancy (Maryland), U.S. Fish and Wildlife Service (Alligator River, Cedar Island, Chincoteague, Great Dismal Swamp, and Pocosin Lakes National Wildlife Refuges), U.S. National Forest Service (Croatan NF), and U.S. National Park Service (Assateague Island NS, Cape Hatteras NS, Great Smoky Mountains NP).