Transactions of the Illinois State Academy of Science received 4/2/20 (2020) Volume 113, pp. 27-30 accepted 8/31/20 Dirca palustris L. (leatherwood, Thymelaeaceae), Distribution and Abundance in Illinois John E. Ebinger1*, Loy R. Phillippe2, Paul B. Marcum2, and William E. McClain3 1Emeritus Professor, Department of Biological Sciences, Eastern Illinois University, 600 Lincoln Avenue, Charleston, IL, 61920. 2Illinois Natural History Survey, Prairie Research Institute, The University of Illinois, 1816 South Oak Street, Champaign, Illinois 61820 3Illinois State Museum, Springfield, IL, 62706 *corresponding author ([email protected]) ABSTRACT During the present study we searched for populations of Dirca palustris L. (eastern leatherwood) throughout Illinois. We started by searching for this species in most herbaria in Illinois, and a few outside the state, to determine potential popula- tion sites. More than 110 specimens of D. palustris were found representing 30 populations. Of these 30 populations identi- fied from herbarium searches, we relocated 16. Nearly all populations were in good-quality mesic upland forests associated with ravines and mostly on N- to NW-facing slopes. During the field trips, extending throughout the growing seasons of 2011 to 2016, we found four previously unreported populations of this species, bringing the total to 20 known populations in Illinois. Keywords: abundance, associates, Dirca palustris, habitat, Illinois, eastern leatherwood, populations INTRODUCTION species, we have always considered it pare historic distribution with current Dirca palustris L. (eastern leatherwood) a plus if we encounter it during a field populations, and to locate previously is a wide-ranging understory shrub of trip. It is generally uncommon to rare unreported populations of this species. eastern North America forests whose throughout the state and the habitat is METHODS geographic range extends from Nova usually given as rich, shaded woods (Mohlenbrock 2002). We reviewed pertinent literature, dis- Scotia, New Brunswick, Quebec, On- cussed the species with local biologists, tario, Minnesota, and eastern North We determined the former presence of and visited most herbaria in Illinois Dakota, south into Oklahoma, Arkan- 30 populations of eastern leatherwood and some larger herbaria in surround- sas, Louisiana, Mississippi, Alabama, in Illinois based on the more than 110 ing states to determine the location of and Florida (Gleason and Cronquist specimens from a search of 19 region- Illinois populations of Dirca palustris. 1991, Ward and Horn 1998). Eastern al herbaria. Though relatively uncom- Listed below are the locations and ac- leatherwood is a member of the fam- mon, this site and habitat specific spe- ronyms of herbaria where specimens ily Thymelaeaceae (Mezereum Fam- cies is not endangered or threatened were examined: Burpee Museum of ily) with more than 500 species that in Illinois (Illinois Endangered Species Natural History, Rockford, Illinois are mostly found in the Eastern hemi- Protection Board 2015). However, (BUR); Chicago Academy of Science, sphere, few species being reported most Botanists rarely encounter east- Chicago, Illinois (CHAS); Chicago for North America. In addition to the ern leatherwood, and even Dr. Loran I. Botanical Garden, Glencoe, Illinois native D. palustris, only the European Nevling (1962), past Chief of the Illinois (CHIC); Northern Illinois University, adventive Thymelaea annua L. (Thyme- Natural History Survey (1987-1993) DeKalb, Illinois (DEK); Eastern Illinois laea) is rarely encountered in Illinois, and authority on the Thymelaeaceae, University, Charleston, Illinois (EIU); being confined to the northeastern on several occasions asked one of us Field Museum of Natural History, Chi- counties (Mohlenbrock 2002). (JEE) if I had encountered this species cago, Illinois (F); Gray Herbarium of Dirca palustris is a small shrub to 2 m during my many trips throughout Il- Harvard University, Cambridge, Mas- tall with jointed, flexuous (zigzag ap- linois. The response was always “still sachusetts (GH); University of Illinois, pearance) twigs and very tough bark; only the population at Fox Ridge State Urbana, Illinois (ILL); Illinois Natural leaves simple, alternate, the blade ellip- Park.” Later, Dr. Nevling informed me History Survey, Champaign, Illinois tic to broadly obovate to ovate, 4-8 cm that he had found two previously un- (ILLS); Indiana University, Blooming- long, with entire margins; petioles 2-5 reported populations in Illinois (Ap- ton, Indiana (IND); Illinois State Mu- mm long; flowers light yellow, 4-mer- pendix, La Salle Co.). This study was seum, Springfield, Illinois (ISM); Illi- ous, 7-10 mm long, appearing before undertaken to determine the present nois State University, Normal, Illinois the leaves. A relatively uncommon status of D. palustris in Illinois, to com- (ISU); Knox College, Galesburg, Illinois Dirca palustris L. (leatherwood, Thymelaeaceae), Distribution and Abundance in Illinois 28 John E. Ebinger, Loy R. Phillippe, Paul B. Marcum, and William E. McClain (KNOX); Missouri Botanical Garden, encountered varied extensively, rang- tion on the reproductive potential of St. Louis, Missouri (MO); The Mor- ing from just a few plants to more than this species across seven years. They ton Arboretum, Lisle, Illinois (MOR); 600, with typically 25-80 individuals determined that shrub size, and, sec- Western Illinois University, Macomb, being found. Some of the populations ondarily, light availability were the Illinois (MWI); Natural Land Insti- were divided into smaller units, with important determinants for fruit pro- tute, Rockford, Illinois (NLI); Rockford groups of individuals in separate and duction. More recently, Peterson et College, Rockford, Illinois (RCH); and adjacent ravines. This was common in al. (2011) studied the variation within Southern Illinois University, Carbon- the two Vermillion County populations and among five populations of eastern dale, Illinois (SIU). We also tried to that had not been previously reported leatherwood scattered from Florida determine the associated species, eco- (Appendix). to eastern North Dakota, and found logical requirements, and other data DISCUSSION phenotypic and genetic differentiation concerning leatherwood from label in- characteristic of limited gene flow, with formation on the herbarium specimens. The habitat specificity and rarity of the northern and southern range lim- Field searches during the growing sea- Dirca palustris has resulted in some its having the most unique phenotypes son from 2010 to 2016 were undertaken interesting studies concerning this and genotypes. In an additional study throughout Illinois, visiting all known species regionally spotty distribution using these same populations, Peterson sites based on herbarium records, and and tendency to aggregate on a local and Graves (2011) found that restricted other sites based on information from scale. Schulz et al. (2004) studied vari- seed dispersal rather than clonal repro- other Illinois Botanists. Nomenclature ation in inflorescence and fruit produc- duction explains the occurrence of D. follows Mohlenbrock (2002). RESULTS Table 1. Populations of Dirca palustris relocated during the present study are list- A specimen collected by George Vasey ed by county along with the original collector, year first collected, present habitat (s.n., Kane Co.: Elgin, May 1862, ILL, with latitude and longitude, the collecting number of Loy R. Phillippe, and the ISM) is the earliest collection of Dirca number of years the population is known to persist (first known collection to our palustris we found for Illinois during study). the herbarium searches. The second oldest was collected by J. T. Stewart County First Collector, Present Habitat Collecting Years (s.n., Peoria Co: Peoria, Illinois, April collecting number and year Latitude and Longitude number 1876, F). We also found herbarium spec- Boone R. Moran s.n./1976 Wooded, NW-facing slope 43619 38 42.41468 -88.92475 imens, or located previous unreported Carroll R.P. Wunderlin 2911/1966 Wooded, N-facing slope 43092 45 populations, from 24 Illinois counties. 42.10007 -90.00902 These were mostly from northern and Coles G. D. Fuller 11048/1945 Wooded, N-facing slope 43387 68 central Illinois counties, but included 39.40224 -88.15587 both Jackson and Pope Counties in the Kane G. Wilhelm 4386/1978 Wooded, N-facing slope 43660 36 southern part of the state (Appendix). 42.14597 -88.28918 Mohlenbrock and Ladd (1978) listed Kankakee R.A. Schneider 542/1937 Wooded, NW-facing slope 43176 75 41.21782 -87.98509 19 counties for this species, includ- La Salle L.I. Nevling 352/1997 Wooded, N-facing slope 43655 17 ing Johnson and Whiteside counties, 41.35007 -89.00674 where we have not recorded voucher L.I. Nevling 353/1997 Wooded, W-facing slope 43002 14 specimens. 41.29388 -89.02828 We relocated 16 populations of Dirca E. Evert 36460/1999 Wooded, W-facing slope 42981 12 41.31186 -88.96963 palustris in 11 Illinois counties (Table Lee G.N. Jones 15837/1943 Wooded, N-facing slope 43010 68 1). Most were from the northern third 41.8508 -89.3464 of Illinois, one from the central part Ogle Fell & Fell 268/1945 Upland, mesic woods 42995 66 of the state (Coles Co.) and three from 42.1452 -89.47286 southern Illinois (Pope Co.). Also, we Pope H.E. Ahles 7499/1953 Wooded, N-facing slope 43978 62 found four previously unreported pop- 37.51922 -88.64539 ulations, one from Jackson County in L. Schopf 1168/1931 Upland, mesic woods 42939 80