Renewable Resources from Wild Sunflowers ( spp., )1

GERALD J. SEILER,2 MERLE E. CARR,3 AND MARVIN O. BAGBy3

Twenty-eight taxa of Helianthus collected throughout the United States and grown in a field nursery were evaluated for yields ofoil, polyphenol hydrocarbon, protein, and ash in above-ground biomass. Hydrocarbons were examinedfor the presence ofrubber, gutta, and waxes. Rubber and gutta were analyzedfor weight­ average molecular weight (Nl}\~ and molecular weight distribution (lvnVD). He­ lianthus ciliaris had the highest oil yield (3.7%) and was analyzedfor yield offatty acids and unsaponifiable matter. Jllost taxa had low pol.vphenol yields «10%), with H. strumosus having the highest (13.9%). Helianthus salicifolius yielded the most hydrocarbon (1.6%) and H. ciliaris had the highest protein content (13.4%). Natural rubber was present in 13 species ofwildsunflowers. Helianthus maximiliani 3 had the lowest Ji71w (29.8 x 10 ), while H. laevigatus had the highest (73.3 x 103). The MvVD ofrubberfrom sunflowers were within the range o/thosefor commercial rubbers. The lower molecular weight rubbers may have potential as plasticizing additives in commercial processing ofsynthetic polyisoprenes and as hydrocarbon feedstock for a synthetic petroleum industry.

Erneuerbare Mittel Von Wilden Sonnenblumen (Helianthus spp., Asteraceae). Achtllndzwanzig Taxa von Helianthus, die iiberall in den Vereinigten Staaten gesammelt wurden und in einer Feldgartnerei angebaut wurden, wurden nach Gehalt von 01, Polyphenol, Kohlenhydrat, Protein, und Asche in der oberirdischen Biomasse bewertet. Kohlenhydrate wurden auf das Vorhandensein von Gummi, Gutta, und Wachs gepriiji. Bei Gummi und Gutta ,vurde das molekulare Durch­ schnittsgewicht (Jll}\~ und die molekulare Gewichtsverteilung (AIWD) analysiert. Helianthus ciliaris hatte den hochsten Olgehalt (3.79b) und del' Gehalt von Fett­ sauren und unverseifien Stoffen war analysiert. Die meisten Taxa hatten niedrige Polyphenolgehalte «10%) und H. strumosus den hochsten (13.9%). Helianthus salicifolius liefene die meisten Kohlenhydrate (1.6%) und H. ciliaris das meiste Protein (13.4%). Natilrliches Gummi war bei 13 Arten von wilden Sonnenblumen vorhanden. Helianthus maximiliani hatte den niedrigsten Ji71w (29.8 x 103) wah­ rend H. laevigatus den hochsten hatte (73.3 x 103). Das lvlWD von Gummi von Sonnenblumen lag innerhalb der Grenzen fill' industriellen Gummi. Das niedrige molekulare Gewicht von Gummi mag ein Potential als plastifizierendes Zusatz­ mittel bei der technischen Verarbeitung von synthetischen Polyisoprenen und als Kohlenhydrat (Futtel) Fiillmasse habell.

Within the past decade, increased attention has been given to the need for developing species as alternative sources offuels, chemicals, feeds, and other

I Received 15 May 1989; accepted 3 February 1990. 2 V.S.D.A., Agricultural Research Service, Conservation and Production Laboratory, Bushland, TX 79012; Present address: V.S.D.A., Agricultural Research Service, Northern Crop Science Laboratory, P.O. Box 5677, Fargo, ND 58105. 3 Research Chemists, V.S.D.A., Agricultural Research Service, Northern Regional Research Center, Peoria, IL 61604.

Economic Botany, 45(1), 1991, pp. 4-15 © 1991, by the New York Botanical Garden, Bronx, NY 10458 1991] SEILER ET AL.: WILD SUNFLOWERS important materials. Such developments could reduce our nation's dependency on foreign sources of many strategic and essential materials and could stimulate economic growth in the United States (Knowles and Lessman 1984). Physical, chemical, and botanical characteristics of about 1100 plant species have been investigated at the U.S.D.A. Northern Regional Research Center, Peo­ ria, Illinois, as potential new plant sources ofindustrial raw materials (Buchanan et al. 1978; Carr 1985; Carr et al. 1985, 1986a, 1986b, 1986c; Carr and Bagby 1987; Cull 1983). The genus Helianthus contains 49 species occurring in a wide range ofhabitats (Schilling and Heiser 1981). In recent years, there has been much interest in developing and utilizing able to tolerate arid and semiarid conditions, particularly for industrial nonfood uses (Davis et al. 1983). Many wild sunflower species inhabit semiarid areas and may be potentially useful in those areas ifthey could serve as sources ofindustrial raw materials. Limited information is available concerning the chemical composition ofwild sunflower species. Forty-eight acces­ sions representing 39 taxa were examined for yields of nonpolar extractables (hydrocarbons, rubber, etc.), polar extractables (resins, sugars, etc.), and crude protein (Adams and Seiler 1984). Several species of Helianthus have been eval­ uated for rubber content, which varied from 0.8% in H. tuberosus to 1.93% in H. radula and H. resinosus (Stipanovic et al. 1980, 1982). The objective of our research was to evaluate 28 taxa of Helianthus collected throughout the United States and grown in a common nursery. Plant materials were analyzed using solvent extractable fractions referred to as "oil," "polyphe­ nol," "hydrocarbon," and "protein."

EXPERIMENTAL Twenty-nine accessions of wild sunflowers representing 28 taxa (5 annual and 23 perennial) were grown in a nursery at Bushland, Texas, in 1982 (Table 1). The plots were arranged in a completely randomized design, with each accession replicated three times. A commercial hybrid, '894', was grown for comparison. Voucher specimens of all taxa were prepared and filed at the U.S.D.A. Conser­ vation and Production Research Laboratory herbarium, Bushland, Texas. Table 1 presents some general information for the species of wild sunflowers analyzed (Rogers et al. 1982). Plant biomass samples were collected as mature above-ground plants and al­ lowed to air dry completely (l5-30°C). The entire sample (400-1000 g) was ground in a Wiley mill to pass through 1-mm diameter holes. Subsamples of milled material were analyzed for moisture (volatiles), ash, and apparent crude protein (6.25 x %Kjeldahl nitrogen). Each milled subsample was extracted in a Soxhlet apparatus with acetone for 48 h, after which acetone was evaporated using a stream of nitrogen. The air-dried extract was partitioned between hexane and water: ethanol (1 :7) to obtain fractions referred to as "oil" and "polyphenol," respectively. After evaporation of the solvents, these fractions were oven-dried (l05°C, 2 h) and weighed for yield. After the 48-h acetone extraction, the residue of each plant sample was extracted with hexane for 48 h to obtain a fraction referred to as "hydrocarbon." The hexane was evaporated with a stream of ni­ trogen and the hydrocarbon was oven-dried (l05°C, 2 h) and weighed for yield. 6 ECONOMIC BOTANY [VOL. 45

If yield of oil was at least 3.0% on a moisture-free plant sample weight basis, the oil was analyzed by thin layer chromatography (TLC) for classes of lipid constituents and, after saponification, for yields of unsaponifiable matter (UM) and free fatty acids (FA). Ifyield ofhydrocarbon was at least 0.4%, the hydrocarbon was analyzed by infrared spectroscopy (IR) to detect the presence ofrubber, gutta, and/or waxes. Rubber and gutta were analyzed for weight-average molecular weight (Mw) and molecular weight distribution (MWD) by gel permeation chro­ matography (GPC). Weight-average molecular weights were calculated by the method of Harmon using a Q factor of 60.4, which is the average ofthe ratios of molecular weight and polymer chain length reported for Hevea and guayule (Swan­ son et al. 1979). Details ofthe various analytical procedures have been described by Carr (1985).

RESULTS AND DISCUSSION Yields of oil, polyphenol, hydrocarbon, and protein are shown in Table 2. Oil yield ranged from 1.0% in H. tuberosus to 3.7% in H. ciliaris (Table 2). These yields were moderate compared to plant species previously analyzed where only 30 species had yields ofat least 6% oil, with a maximum of 11 % oil in Euphorbia dentata Michx. (Carr and Bagby 1987). Polyphenol yields were also moderate, varying from 2.9% in H. pumilus to 13.9% in H. strumosus (Table 2). A polyphenol yield of 20% is considered high (Carr and Bagby 1987). All but one species ofwild sunflower (H. strumosus) had less than a 10% polyphenol yield. Of 1100 species previously examined, about 100 had polyphenol yields of 15%, and only 1% had yields of 20% or more (Carr et al. 1985). Species yielding substantial amounts ofboth oil and polypheno1 are atypical and are generally trees or shrubs, particularly evergreens (Carr et al. 1986c). Yields of hydrocarbon were at least 0.6% in 12 of the sunflower species. The lowest yields <0.1% were found in H. argophyllus, H. debilis ssp. silvestris, H. petiolaris ssp. petiolaris, and H. pumilus. The first three species are annual, and the last is perennial. The highest yield ofhydrocarbon was found in H. salicifolius (1.6%), a perennial (Table 2). With few exceptions, yields of hydrocarbon have been low «2%) for over 1000 species collected from various regions ofthe United States (Carr 1985; Roth et al. 1982). Protein content of wild sunflower plant samples varied from 3.8% in H. tu­ berosus to 13.4% in H. ciliaris (Table 2). Cultivated sunflower, H. annuus, had a higher protein content (20.4%) than the wild sunflowers. In general, plant protein contents were lower than those previously reported for wild sunflowers (Adams and Seiler 1984; Seiler 1986). The difference in protein levels could be due to the different sampling times, different plant parts, and nitrogen fertility. The perennial species H. ciliaris, the only species to have an oil content greater than 3%, was analyzed further by TLC (Table 2). The lipid fraction contained a trace ofhydrocarbon, 25% unsaponifiable lipids (UM), and 53% fatty acids (FA). Extracted oils ofmost aboveground plant samples analyzed previously have con­ tained about 40-60% UM (Carr et al. 1985). The combined UM + FA yield for H. ciliaris was 78%, which is on the lower end of the range when compared to most plant oils previously analyzed where combined amounts of UM and FA TABLE 1. GENERAL INFORMATION FOR SPECIES OF SUNFLOWER ANALYZED. a '<) '<) .::

Primary Herbarium Annual geographic Species voucher Life Height, General precip. , Collection distribution (common name) number Cycle m habitat cm site in U.S.

Helianthus angustifolius L. ANG-385 pb to 2.0 Swampy 90-175 Alvin, New York to Florida (narrow leaf sunflower) TX west to and Texas en m F !L.. .illl!!lli!§. L. ANN-894 A to 1.5 Variable m ::<:J (cultivated hybrid '894') m --I ;J> !L.. .illl!!lli!§. L. ANN-376 A to 4.0 Variable, 25-100 La Porte, Widespread, especially (annual sunflower) disturbed TX west of Mississippi r. areas River ~ F t:I !L.. argophyllus T. & G. ARG-1575 A to 4.0 Sandy 50-100 Daytona East Texas, Florida en c:: (silver-leaf sunflower) Beach, FL Z ;!J !L.. arizonensis R. Jackson ARI-803 p to 0.5 Light 25-50 Snowflake, Arizona, west New o ~ (Arizona sunflower) soils AZ m ::<:J en !L.. californicus DC. CAL-772 p to 3.0 Wet, 25-127 Knoxville, Central to south ( sunflower) rocky CA California

!L.. ciliaris DC. CIL-IOO p to 0.7 Dry, wet, 50-75 Bushland, Oklahoma, west Texas, (Texas blueweed sunflower) alkaline TX south Arizona, north Mexico

!L.. debilis Nutt. ssp. DEB-SIL­ A to 2.0 Sandy 75-115 Henderson, Southeast Texas silvestris Heiser 1286 TX (forest sunflower)

!L.. decapetalus L. DEC-1688 P to 2.0 Shady 60-140 Linville, Massachusetts to Iowa, (ten-petal sunflower) woods NC south to north Georgia --J TABLE 1. CONTINUED. 00

Primary Herbarium Annual geographic Species voucher Life Height, General precip. , Collection distribution (common name) number Cycle m habitat cm site in U.S.

J:!. divaricatus L. DIV-830 P to 1.5 Dry 75-140 Wister, South Quebec to (divaricate sunflower) rocky OK Wisconsin, south to north Florida and Oklahoma

~ grosseserratus Martens GRO-688 P to 5.0 Prairie 50-127 Stuart, Maine to South Dakota, (saw-tooth sunflower) OK south to Texas ntTl 0 Z ~ hirsutus Raf. HIR-828 P to 2.0 Dry, 63-140 Wilburton, Pennsylvania to 0 (stiff-hair sunflower) open OK Minnesota, south to 3:: Georgia, northern n I:l:l Nuevo Leon, Mexico 0 -I ;J> ~ laciniatus Gray LAC-8l0 P to 1.2 Dry 25-60 San Lorenzo, Nuevo Leon, Mexico Z (jagged-edge sunflower) slopes NM southwest New Mexico --<

~ laevigatus T. & G. LAE-906 P to 2.2 Shale 90-127 Webster, Virginia, West (smooth sunflower) barrens VA Virginia, North Carolina, South Carolina

~ maximiliani Schrad. MAX-62l P to 2.0 Prairie 25-127 Gatesville, Massachusetts, (Maximilian's sunflower) TX southeast to Texas, north to Canada

~ microcephalus T. & G. MIC-863 P to 1.5 Partially 76-180 Coosa, GA New Jersey to south (small-head sunflower) open wood Michigan to northeast Arkansas, south to <: north Florida and 0 Alabama r v,... TABLE 1. CONTINUED. -0 -0

Primary Herbarium Annual geographic Species voucher Life Height, General precip. , Collection distribution (common name) number Cycle m habitat cm site in U.S.

!:!. mo11is Lamb. MOL-672 P to 1.2 Dry, open 90-140 Okmulgee, Massachusetts to (ashy sunflower) OK Wisconsin, south to north Georgia, east Texas

CIl !:!. occidentalis Rid. OCC-OCC- P to 1.5 Dry, sand 65-140 Raymondville, Wisconsin to rI'T1 ssp. occidentalis 878 MO Louisiana, Florida I'T1 (few-leaf sunflower) ;0 I'T1 >-I ~ petiolaris Nutt. PET-PET- A to 2.0 Sand 38-127 Adrian, TX Scattered throughout >- ssp. petiolaris 528 U.S., especially the r. (prairie sunflower) Central Plains :::: r H. pumilus Nutt. PUM-735 P to 1.0 Rocky 25-65 Boulder, CO Central and southeast 0 CIl (dwarfish sunflower) soil Wyoming to central c: Colorado Z 'Tl r 0 ~ resinosus Small RES-834 P to 3.0 Variable 127-178 Ora, MS North Carolina to :::: (resinous sunflower) northwest Florida to I'T1 ;0 Mississippi CIl

H. rigidus (Cass.) Desf. RIG-SUB- P to 1.2 Dry 38-90 Leydon, CO South Ontario to south ssp. subrhomboides 737 prairie Alberta, south to west (Rydb.) Heiser Texas (stiff sunflower)

~ salicifolius Dietr. SAL-617 P to 3.0 Limestone 76-115 Muenster, West , east (willow-leaf sunflower) soils TX , south to north Texas

~ silphioides Nutt. SIL-831 P to 3.0 Open 114-140 Wister, OK Tennessee to south (odorous sunflower) areas Illinois, Missouri, south to Louisiana -0 o

TABLE 1. CONTINUED.

Primary Herbarium Annual geographic Species voucher Life Height, General precip. , Collection distribution (common name) number Cycle m habitat cm site in U.S.

J:!. simulans Watson SIM-837 P to 2.6 Wet, Il,O -150 Pensacola, Florida and Louisiana (simulans sunflower) mucky FL rnn J:!. smithii Heiser SMI-860 P to 1.5 Shale 90-127 Morganton, Northeast Georgia and o (Smith's sunflower) barrens NC east Alabama oZ :::: J:!. strumosus L. STR-852 P to 2.0 Variable 65-140 Silver City Massachusetts to Pi (pale-leaved wood NC Minnesota, south to oO:l sunflower) Texas, east to Florida S; z !:L. tuberosus L. TUB-346 P to 2.6 Swampy 50-140 Nocona, TX Massachusetts to North --< (Jerusalem artichoke) Dakota, south to Texas, east to Florida

!:L. x laetiflorus Pers. XLAET-654 P to 1.2 Prairie 75-115 Mullen, NE Massachusetts to (showy sunflower) Nebraska, southeast to Georgia --- a After Rogers et al. 1982. b A - Annual; P - Perennial.

'

Yield %a

Species Ash Oil Polyphenol Hydrocarbon Proteinb TotalC

Helianthus angustifolius 14.8 1.2 5.7 0.4 6.8 14.1 Ul ~ annuus (cultivated) 19.5 2.1 8.8 0.1 20.4 31.4 rtTl ~ .illl!:lllli§. ( tTl wild) 17.9 2.0 6.5 0.2 13.1 21.8 ::

TABLE 2. CONTINUED.

Yield %a

C Species Ash Oil Polyphenol Hydrocarbon Proteinb Total tTl n 0 Z 0 J:L.. simulans 12.4 1.3 7.0 0.3 5.0 13 .6 3:: J:L.. smithii 7.2 2.1 5.6 1.0 5.2 13.9 () ttl J:L.. strumosus 10.4 2.0 13.9 0.7 7.1 23.7 0 -I J:L.. tuberosus 8.5 1.0 6.2 0.5 3.8 n.5 ;J> z J:L.. x laetiflorus 14.6 1.7 9.4 1.1 5.6 17.8 .-<

a % is on a moisture free plant sample weight basis. b Protein = % Kjeldahl nitrogen x 6.25. c Total = oil + polyphenol + hydrocarbon + protein.

'

TABLE 3. WEIGHT-AVERAGE MOLECULAR WEIGHT (Mw) AND MOLECULAR WEIGHT DISTRIBUTION (MWD) VALUES OF PLANT RUBBERS.

MWD Species Mw x 103 (lV!w/lV!n)a

!L.. californicus 49.93 2.62 !L.. decapetalus 40.11 2.64 !L.. grosseserratus 32.21 2.68 !L.. hirsutus 41. 52 2.61 !L.. laevigatus 73.29 3.10 !L.. maximiliani 29.83 2.57 !L.. resinosus 42.09 2.14 !L.. rigidus ssp. 34.63 2.65 subrhomboideus !L.. salicifolius 29.91 2.62 !L.. smithii 50.22 2.64 !L.. strumosus 61.24 2.53 !L.. tuberosus 32.74 2.37 !L.. K laetiflorus 65.81 2.54

a MW and MWD values were determined by GPCi Hn = number average molecular weight (Swanson et al., 1979). frequently were in the range of70-90% ofthe oil sample (Carr et al. 1986a). These amounts are dependent, to a large extent, upon the amounts of polar organic material removed by partitioning from the FA fractions before drying and weigh­ ing and on the amounts ofvolatile components lost from the UM and FA fractions during oven drying (lOSoC, 2 h). Thirteen species ofsunflower that yielded at least 0.4% hydrocarbon were ana­ lyzed by IR spectroscopy to detect the presence of rubber, gutta, and/or waxes (Table 3). Natural rubber was present in all 13 species. Helianthus maximiliani 3 had the lowest JWW (29.8 x 10 3), and H. laevigatus had the highest (73.3 x 10 ) 3 (Table 3). As for most plants, the values ofMWs are low «75.0 X 10 ) compared 6 to rubbers from guayule (Parthenium argentatum A. Gray) (1.28 x 10 ) and Para 6 rubber (Hevea brasiliensis (Willd. ex A. Juss) Muel!. Arg.) (1.31 x 10 ) (Swanson et al. 1979). However, low molecular weight rubbers may have potential as plas­ ticizing additives in commercial processing ofhigh molecular weight natural and synthetic polyisoprenes and as hydrocarbon feedstocks for a synthetic petroleum industry (Buchanan et al. 1980). Polydispersity characteristics (mixing and blending) of rubbers improve with increases in their MWD. Molecular weight distributions for wild sunflower varied from 2.14 for H. resinosus to 3.10 for H. laevigatus (Table 3). Most MWDs are within the range ofthose for commercial rubbers (Swanson et al. 1979). Swanson et al. (l979) reported that the rubber in H. hirsutus had a molecular weight (2.79 x 10 5) and polydispersity factor (3.1) that could produce a potentially useful natural rubber. Values for the population ofH. hirsutus we evaluated were lower due perhaps to environmental effects or genetic variation within species. Wild sunflower species contain plant oil concentrations that were moderate compared to 1000 other analyzed plant species. H elianthus ciliaris had the highest 14 ECONOMIC BOTANY [VOL. 45 oil concentration (3.7%). Plant oil yields of 6% or above are considered high and have been found in only 30 species. Polyphenol yields of wild sunflowers were moderate, with H. strumoslls yielding 13.9%. A polyphenol yield of 20% is con­ sidered high. Hydrocarbon yields ofwild sunflowers were average for most species, with H. salic(foliliS having the highest level (1.6%), which would rank the species as a high producer compared to other species previously analyzed. Five taxa (H. californiclls, H. grosseserratlls, H. salicifolillS, H. smithii, and H. x laetifloJ'lls) were identified as rubber-producing species with 1.0% or more hydrocarbon yield. Plant protein concentrations ofwild sunflowers were generally low for utilization as a sole source offeed for livestock. The highest protein concentration was found in H. ciliaris (13.4%). Low molecular weight rubber was found in 13 species ranging 3 in weight from 29 x 10 to 73 X 103• These molecular weights are low compared to other plants previously analyzed. Most MWDs ofrubber from wild sunflowers were within the range ofcommercial rubbers. Low molecular weight rubbers from wild sunflowers have potential as plasticizing additives in commercial processing ofhigh molecular weight natural and synthetic polyisoprenes and as hydrocarbon feedstocks for a synthetic petroleum industry.

ACKNOWLEDGMENTS

We wish to thank James R. Cresap for collection of samples and Dale W. Ehmke for analytical assistance.

LITERATURE CITED

Adams, R. P.. and G. J. Seiler. 1984. Whole-plant utilization of sunflowers. Biomass 4:69-80. Buchanan. R. A.. 1. M. Cull. F. H. Otey. and C. R. Russell. 1978. Hydrocarbon- and rubber-producing crops: evaluation of U.S. plant species. Econ. Bot. 32: 131-145. --. F. H. Otey. and M. O. Bagby. 1980. Botanochemicals. Recent Advances Phytochem. 14: 1­ 22. Carr. M. E. 1985. Plant species evaluated for new crop potential. Econ. Bot. 39:336-345. --. and M. O. Bagby. 1987. Tennessee plant species screened for renewable energy sources. Econ. Bot. 41 :79-85. --. M. O. Bagby. and W. B. Roth. 1986a. High oil- and polyphenol-producing species of the Northwest. J. Amer. Oil Chern. Soc. 63:1460-1464. --. C. T. Mason. and M. O. Bagby. 1986c. Renewable resources from Arizona trees and shrubs. Forest Ecol. Managem. 16:155-167. --. B. S. Phillips. and M. O. Bagby. 1985. Xerophytic species evaluated for renewable energy resources. Econ. Bot. 39:505-513. --. B. S. Phillips. and M. O. Bagby. 1986b. Potential resource materials from Ohio plants. Econ. Bot. 40:434-441. Cull. 1. M. 1983. Midwest plants for potential crops. Trans. Illinois State Acad. Sci. 76:203-212. Davis. J. B.• D. E. Kay. and V. Clark. 1983. Plants tolerant of arid or semiarid conditions with nonfood constituents of potential use. Pages 1-172 in Report of the Tropical Products Inst. G 150. Tropical Products Inst.. London. Knowles. P. F.. and K. J. Lessman. 1984. Development of new crops: needs. procedures. strategies. and options. Pages 1-30 in Council for Agricultural Science and Technology Report No. 102. Headquarters Office. Ames. IA. Rogers. C. E.• T. E. Thompson. and G. J. Seiler. 1982. Sunflower species of the United States. National Sunflower Association. Headquarters Office. Bismarck. ND. Roth. W. B.. 1. M. Cull. R. A. Buchanan. and M. O. Bagby. 1982. Whole plants as renewable energy resources: checklist of508 species analyzed for hydrocarbon. oil. polyphenol. and protein. Trans. Illinois State Acad. Sci. 75:217--231. 1991] SEILER ET AL.: WILD SUNFLOWERS 15

Schilling, E, E., and C B, Heiser, 1981, Infrageneric classification ofHelialllhus (Cornpositae), Taxon 30:393-403, Seiler, G, J, 1986, Forage quality of selected wild sunflower species. J. Arner, Soc. Agron. 78:1059­ 1064. Stipanovic, R. D., D. H. O'Brien, C. E. Rogers, and K. Hanlon. 1980. Natural rubber from sunflower, J. Agric. Food Chern. 28:1322-1323. ---, G. J. Seiler, and C E. Rogers. 1982. Natural rubber from sunflower, J. Agric. Food Chern. 30:611-613. Swanson, C L, R. A. Buchanan, and F. H. Otey. 1979. Molecular weights of natural rubbers from selected temperate zone plants. J. Appl. Polym. Sci. 23:743-748.