Author Institution: Department of Botany and Plant Pathology, The Ohio State University, Columbus, Ohio 43210The genus Silphium is represented in Ohio by four species, S. perfoliatum L., S. trifoliatum L., S. laciniatum L., and S. terebinthinaceum Jacqs. Two of these species, S. laciniatum and S. terebinthinaceum, have hybridized in a prairie habitat west of Marion, Ohio. This population has been analyzed using the Gay Method of population analysis. In contrast to a similar population of hybridizing individuals from Coles County, Illinois, where backcrossing is apparently in the direction of S. laciniatum, backcrossing in the Marion, Ohio, population appears to be in the direction of S. terebinthinaceum

Fisher, T. Richard

The Ohio Journal of Science

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THE GENUS SILPHIUM IN OHIO1- 2T. RICHARD FISHERDepartment of Botany and Plant Pathology, The Ohio State University, Columbus, Ohio 1^3210ABSTRACTThe genus Silphium is represented in Ohio by four species, 51. perfoliatum L., S. tri-foliatum L., 5. laciniatum L., and S. terebinthinaceum Jacqs. Two of these species, S.laciniatum and 5. terebinthinaceum, have hybridized in a prairie habitat west of Marion,Ohio. This population has been analyzed using the Gay Method of population analysis.In contrast to a similar population of hybridizing individuals from Coles County, Illinois,where backcrossing is apparently in the direction of S. laciniatum, backcrossing in theMarion, Ohio, population appears to be in the direction of S. terebinthinaceum.The genus Silphium is represented in Ohio by four species: S. perfoliatum L.,5. trifoliatum L., S. laciniatum L., and S. terebinthinaceum Jacqs. The objectiveof this paper is to describe their taxonomy, morphology, ecology, and hybridizationas it is known in Ohio. A natural hybridizing population is analyzed by thehybrid number method of Gay (I960), which is a modification of the hybrid indexmethod of Anderson (1949).KEY TO SPECIES IN OHIOStems leafyLeaves connate—perfoliate; stems quadrangular 1. S. perfoliatumLeaves usually with short petioles, commonly verticillate in 3's or 4's, sometimesalternate 2. S. trifoliatumStems naked except a few reduced leavesLeaves pinnatified or bipinnatified; flowering stems with hispid or hirsute spreadinghairs 3. S. laciniatumLeaves elliptic, sharply toothed, not pinnatified; stems glabrous or essentially so4. S. terebinthinaceum1. S. perfoliatum L. ssp. perfoliatum. Cup-plantPerennial, stem conspicuously angled, 1-3 m tall, glabrous or with a few scattered hairsnear the base. Leaves with connate-perfoliate bases, blades broad at base, nearly deltoid tobroadly ovate, irregularly toothed, scabrous above, hispid below. Upper stems branchedbearing numerous heads. Bracts of inflorescence ovate in 2 or 3 series, glabrous except onciliate margins. Ray flowers 20-25. Achenes obovate with well developed wings, sinus deep.Woodland margins, along streams and bottom land. Widely distributed in Ohio. Thisspecies can be hybridized artificially with S. trifoliatum, but no natural hybrids are knownto occur in Ohio. Silphium perfoliatum ssp. connatum (L.) Cruden occurs in the mountainousregions of West Virginia, Virginia and North Carolina and is not known to occur in Ohio. Abiosystematic treatment of this species will appear elsewhere.2. S. trifoliatum L.Perennial with thick, fibrous roots, creeping. Stem glabrous, often slightly glaucous,.1-2 m. tall. Leaves often verticillate in 3's or 4's, but just as often merely opposite or occa-sionally alternate; leaf blades lanceolate to ovate-lanceolate, toothed, usually scabrous above.Heads many, bracts imbricate, subequal, glabrous except for ciliolate margins; rays lightyellow, averaging 9. Achenes orbicular to ovate, wing pointed at apex. Woodlands andprairies.This species has been treated by some authors as being composed of two taxa, varietytrifoliatum and variety latifolium based on pubescence of leaves and frequency of trifoliatenessof leaves, the latter variety most commonly glabrous and leaves merely opposite. These twovarieties are represented in Ohio. The biosystematics of these varieties is under intensivestudy by Mr. Wallace Weber and results of this investigation will be reported elsewhere.Publication Number 682 of the Department of Botany and Plant Pathology. This projectwas supported, in part, by the National Science Foundation (NSF-GB1306) and is gratefullyacknowledged. Recognition and appreciation is also rendered Mrs. Mildred Stalder, Mrs.Clara M. Frederick, Mr. Wilbur Settle, Mr. Thomas Boggs and Mr. Jack Cooke, who aidedin the statistical analysis.2Manuscript received February 24, 1965.THE OHIO JOURNAL OF SCIENCE 66(3): 259, May, 1966.260 T. RICHARD FISHER Vol. 66In Ohio, this species has been collected in 14 counties, in both glaciated and unglaciatedregions. Some evidence based on studies by Mr. Weber indicates that plants from these twoareas represent at least ecotypes.3. Silphium laciniatum L. Compass-plantPerennial, coarse and rough, taproot 3-5 inches thick at crown, extending 1-3 feet in ground.Stem 2-3 m. tall, hispid of spreading hairs. Leaves alternate, mostly basal, reduced upward,deeply pinnatifid or even bipinnatifid, hispid to hirsute. Heads 10-15 and usually shortpeducled to nearly sessile; bracts acuminate, imbricate, hispid, often refiexed with age; rays15-30, yellow. This species is extremely rare in Ohio; in fact, I have seen it growing fromonly one station near Wilgus in Lawrence County. Evidence from studying material in theherbarium of The Ohio State University indicates that this species was much more abundantin central and west central Ohio at about the time when these areas were beginning to be ex-tensively cultivated. Hybridication with the next species, S. terebinthinaceum, is known tooccur occasionally in localities in Indiana and Illinois where it grows in more dry prairie sites.FIGURES 1-4. Distribution of the genus Silphium in Ohioas represented in the herbarium of The OhioState University. Figure 1, S. perfoliatumL., figure 2, S. trifoliatum L., figure 3, S. laci-niatum L., figure 4, S. terebinthinaceum Jacq.4. S. terebinthinaceum Jacqs. Prairie dockPerennial with very thick taproot similar to the preceding species. Stem 6-8 feet tall,essentially glabrous, leafless or essentially so. Leaves basal, large and long petiolate, theblade broadly ovate, cordate at base, sharply toothed, scabrous to glabrous. Upper stemsbranched, glabrous, heads numerous, bracts imbricate, glabrous, elliptic, inner slightly oblong,rays 12-25. Achenes obovate with narrow wing. This species is abundant in the wet prairiesof central, north central, and north western Ohio. One recognizable variety is variety lucy-braunii Sterr. and is associated with smaller prairie outcrops in southern Ohio, particularlythose of Adams County.This species hybridizes with S. laciniatum L. and the hybrid is likely to be confused withS. pinnatifidum Ell., which does not occur in Ohio.HYBRIDIZATION STUDYSilphium laciniatum L. and S. terebinthinaceum Jacqs. are known to hybridizein several localities in Illinois and Indiana where their ranges overlap (Fisher, 1959).No. 3 THE GENUS SILPHIUM 261However, the hybridizing population I have examined in Ohio is significantlydifferent from hybridizing populations in Illinois and Indiana and deserves specialmention.Several reputed hybrids between those two species are in the herbarium of TheOhio State University. A number of specimens were collected several years agoin Franklin County by Prof. J. H. Schaffner. These locations have been visitedand the hybrids are apparently not present; in fact, some of these locations arepresently occupied by housing developments near Columbus. One populationwest of Marion, Ohio, in Marion County, was visited in the summer of 1959 andon numerous occasions since for the purpose of assembling population samples.In 1960, several clones were removed to the research garden at The Ohio StateUniversity for further study.One of the obvious differences in the Marion County, Ohio, population is that,in addition to the occasional hybrid, there is rather extensive backcrossing in thedirection of S. terebinthinaceum. In the Illinois and Indiana populations, thedegree of backcrossing was difficult to determine but was in the direction ofS. laciniatum. In the Marion County, Ohio, population, there is only one parentspecies represented, S. terebinthinaceum. The nearest station for S. laciniatumis nearly 200 miles to the southeast.hybrid indexFIGURE 5. Graph of the hybrid number and hybrid index as applied to hybridizing populationof 5. terebinthinaceum and 51. laciniatum. The numbers adjacent to the glyphsrepresent the numbers of plants graphed at that point.Methods of analyzing population. The method used in this study is called thehybrid number method (Gay, 1960) and is a modification of the hybrid indexmethod described by Anderson (1949). It is a modification in that it is used incombination with the hybrid index method. Its chief advantage is that it permitsmeaningful averages of introgressing populations. Comparison between variouspopulations can be made visually, by graphing the mean hybrid number againstthe mean hybrid index.The hybrid index was prepared by scoring the following characters: numberof leaf lobes, angle of lateral vein (third from leaf base) and midrib, total of lateralveins, number of hairs per unit area (6 square mm), and width of blade at broadestpoint. These characters were selected because by these characters these twospecies are easily separated.The range of raw scores for each plant is included in table 1. The raw scoreswere grouped and given values from 0-5, except pubescence which was scoredon a 0-3 scale. Therefore, the total hybrid index for a plant representative ofS. terebinthinaceum would be 0, while a plant representative of S. laciniatum wouldbe at the highest or 18.After the hybrid index for each plant was computed, its hybrid number wasdetermined in the following manner. Since the hybrid index scale extends from0-x, the hybrid number scale extends from 0 to x/2. From the hybrid index0 to x/2, the hybrid number equals the hybrid index. From the hybrid indexx/2 to x, the hybrid number equals x minus the hybrid index. In this population,262 T. RICHARD FISHER Vol. 66x equals 18, since this is the greatest possible score an individual could receive,and is representative of S. laciniatum. From these data, the mean hybrid indexand mean hybrid number of the population is computed.Results of population analysis. The apex of the triangle formed by the glyphsin figure 5 represented the most hybrid nature possible for any individuals, becausetheir hybrid index is 9 and their hybrid number is 9. Two plants collected fromthis population are graphed at this point. These plants compare favorablyTABLE 1. Measurements of 28 plants of a hybrid population of Silphium near Marion, OhioPlant no. No. oflobesAngle oflateralveinsNo.lateralveinsNo. hairs perunit area(6 mm2Width ofblade atbroadest pointHybridindexHybridnumber12345678910111213141516171819202122232425262728262129271726201722101280031000000000000(5)(4)(5)(5)(3)(5)(3)(3)(4)(1)(2)(1)(0)(0)(0)(0)(0)(0)(0)(0)(0)(0)(0)(0)(0)(0)(0)(0)70°55°70°75°70°58°65°85°60°55°55°75°100°90°60°90°85°90°85°85°93°96°94°96°98°100°96°95°(2)(4)(2)(2)(2)(4)(3)(1)(3)(4)(4)(2)(0)(0)(3)(0).(1)(0)(1)(1)(0)(0)(0)(0)(0)(0)(0)(0)31284033392429363734404534523832382839505051555653454850(3)(3)(2)(3)(2)(4)(3)(2)(2)(2)(2)(1)(2)(0)(2)(3)(2)(3)(2)(0)(0)(0)(0)(0)(0)(1)(1)(0)4813310044161810419371362720132117064010886(3)(1)(0)(0)(0)(0)(3)(1)(1)(1)(3)(0)(2)(1)(0)(2)(1)(1)(1)(1)(0)(0)(0)(0)(1)(0)(0)(0)21.418.522.520.818.419.523.119.022.223.022.027.122.827.524.528.519.825.532.229.132.230.033.634.333.234.536.032.6TotalMean(2)(2)(2)(2)(2)(2)(2)(2)(2)(2)(2)(1)(2)(1)(1)(1)(2)(1)(0)(1)(0)(0)(0)(0)(0)(0)(0)(0)15141112915149121013562666543010011101816.134760349685562666543010011101113.2morphologically to the artificial hybrid from the research field at The Ohio StateUniversity. Nine plants are graphed as hybrids between the hybrid peak andS. laciniatum, although 5 are closer to the hybrid peak. Seventeen plants aregraphed along a line from the hybrid peak and 5. terebinthinaceum. There are noplants representative of S. laciniatum in the population. All totaled, more plantsof the population have scores ranging between S. terebinthinaceum and the hybridpeak than between the hybrid peak and S. laciniatum. This would be expected ifbackcrossing in this natural population is in the direction of S. terebinthinaceum.With this modified hybrid index method, a single specimen can be represented interms of hybridity, since the hybrid index measures the hybridity from S. tere-binthinaceum and S. laciniatum while the hybrid number is a measure of hybridityfrom either "pure" species and the Fi hybrid. Another advantage of this methodis that one can compare more than one population visually by graphing the meanhybrid number against the mean hybrid index. This permits graphing an entirepopulation at one point and several populations can be included on the same graph.No. 3 THE GENUS SILPHIUM 263In figure 6, a population from Coles County, Illinois (Fisher 1959), is comparedwith the population from Marion County, Ohio. Backcrossing is occurring inthe direction of S. laciniatum in the Illinois population (B), while backcrossing isoccurring in the direction of S. terebinthinaceum in the Ohio population (A).Artificial hybridizations. Although S. terebinthinaceum and S. laciniatumhybridize occasionally in nature, they can be caused to hybridize in the researchgarden only with difficulty. Since 1957, attempts to hybridize these two specieshave resulted in only 3 Fx hybrids. Meiosis in the hybrids is normal and stain-ability of pollen averages 73%. Seed-set in the Fj hybrid is high, averaging 98%.Morphologically, this hybrid is intermediate and is similar to two plants collectedFIGURE 6. Graph of mean hybrid number (vertical axis) and mean hybrid index (horizontalaxis) of two populations of Silphium: population A from Coles County, Illinois,and population B from Marion County, Ohio.at the Marion, Ohio, station, to one plant at the Switz City, Indiana, station,but to no plants at the Coles County, Illinois, station, since the latter stationrepresents plants as backcross segregates to 5. laciniatum.SUMMARY AND CONCLUSIONSThe genus Silphium in Ohio consists of 4 species, although S. laciniatum isquite rare and consists of only one known colony. Before cultivation of the land,particularly the prairies in Ohio, these species were probably widely distributed.Today, S. terebinthinaceum and 5. trifoliatum may be found primarily as prairierelics along railroads and highways. Silphium perfoliatum is widespread in Ohio.Silphium terebinthinaceum and S. laciniatum have hybridized in the past, asevidenced by a hybrid population west of Marion, Ohio. In this population,backcrossing and hybrid segregation appear to be in the direction of S. tere-binthinaceum. Analysis of the population indicates that, statistically, 9 of the28 plants sampled represent varying degrees of hybridity ranging from the Fi toS. laciniatum, although no hybrid plants are especially near S. laciniatum.Furthermore, 4 plants of the described population are statistically S. tere-binthinaceum and 13 range in hybridity from typical S. terebinthinaceum to thestatistical Fi hybrid. In contrast, in a population from Coles County, Illinois,backcrossing is apparently in the direction of S. laciniatum.LITERATURE CITEDAnderson, Edgar. 1949. Introgressive Hybridization. John Wiley and Sons, New York.109 p.Fisher, T. Richard. 1959. Hybridization between Silphium laciniatum L. and S. terebinthi-naceum Jacq. Brittonia 11: 250-254.Gay, Peter. 1960. A new method for the comparison of populations that contain hybrids.New Phytol. 59: 218-226.

The Genus Silphium in Ohio

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The Genus Silphium in Ohio

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