A second population of Phemeranthus calycinus (Montiaceae, large-flowered rock pink) was confirmed for southwestern Illinois. This is the second site known east of the Mississippi River for this taxon.
Phemeranthus calycinus (Engelm.) Kiger (Montiaceae)
Monroe County: open, nearly level outcrop of Au Vase sandstone, 35 m x 85 m, adjacent to an unnamed tributary of Horse Creek in the southern part of the county. Exact geographic coordinates are withheld to ensure the privacy, protection and viability of the population. W. McClain #2764, 5 August 2010, Eastern Illinois University (EIU).
Significance: A population of Phemeranthus was incidentally discovered in southern Monroe County during the summer of 2001. This population, field identified as P. calycinus, was included as a rare species record in the Illinois Department of Natural Resources Natural Heritage database (Herkert and Ebinger 2002). However, species confirmation remained uncertain for several years. The herbarium specimen (W. McClain #2764) obtained in 2010 was assigned to P. rugospermus (Engelm.) Kiger (wrinkle-seeded rock pink) following deposition in the Eastern Illinois University Herbarium. However, morphological characters, including stamen numbers, style lengths, and seed coat characteristics observed on living plants at the discovery site suggested the need for a re-evaluation of this designation. Accordingly, two living plants from Monroe County and two from a known population of P. rugospermus in Mason County, Illinois were obtained, and grown under greenhouse conditions. Plant size, growth habit, and flower characters were compared, confirming the Monroe County individuals to be P. calycinus (Engelm.) Kiger.