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Humulus lupulus
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<h2 id="description">Description</h2> <p><i>Humulus lupulus</i> is a perennial <a href="/facts/Herbaceous_plant/u6myDhE2">herbaceous plant</a> up to 10 metres (33 feet) tall, living up to 20 years.<a class="footnote-ref" id="fnref:3" href="#fn:3"><sup>3</sup></a> It has simple <a href="/facts/Leaves/1m6wCNTg">leaves</a> with 3–5 deep lobes that can be opposite or alternate.<a class="footnote-ref" id="fnref:4" href="#fn:4"><sup>4</sup></a> The species is triggered by the longer summer days to flower,<a class="footnote-ref" id="fnref:5" href="#fn:5"><sup>5</sup></a> usually around July or August in the Northern Hemisphere.<a class="footnote-ref" id="fnref:6" href="#fn:6"><sup>6</sup></a> The plant is <a href="/facts/Dioecious/jwMHLkuM">dioecious</a>, with male and female flowers on separate plants. The fragrant flowers are <a href="/facts/Wind-pollinated/37MXM06c">wind-pollinated</a>.<a class="footnote-ref" id="fnref:7" href="#fn:7"><sup>7</sup></a> The staminate (male) flowers do not have petals, while the pistillate (female) flowers have petals enveloping the fruit. The female flower cones (or <a href="/facts/Strobili/WEVJDExF">strobili</a>) are known as <a href="/facts/Hops/mBRf6xGx">hops</a>.<a class="footnote-ref" id="fnref:8" href="#fn:8"><sup>8</sup></a> The fruit is an <a href="/facts/Achene/8dm9UxMy">achene</a>, meaning that it is dry and does not split open at maturity.<a class="footnote-ref" id="fnref:9" href="#fn:9"><sup>9</sup></a> The achene is surrounded by tepals and lupulin-secreting glands are concentrated on the fruit.<a class="footnote-ref" id="fnref:10" href="#fn:10"><sup>10</sup></a><a class="footnote-ref" id="fnref:11" href="#fn:11"><sup>11</sup></a> </p><p>The species is sometimes described as a <a href="/facts/Bine_(botany)/3nVRIAws">bine</a> rather than a vine because it has stiff downward facing hairs that provide stability and allow it to climb.<a class="footnote-ref" id="fnref:12" href="#fn:12"><sup>12</sup></a> </p> <h3>Chemistry</h3> <p><i>H. lupulus</i> contains <a href="/facts/Myrcene/Y2tR3rlN">myrcene</a>, <a href="/facts/Humulene/PswJ9FPm">humulene</a>, <a href="/facts/Xanthohumol/HPTtXzrz">xanthohumol</a>, <a href="/facts/Myrcenol/fHXPrpJI">myrcenol</a> and <a href="/facts/Linalool/abBM1jXB">linalool</a>,<a class="footnote-ref" id="fnref:13" href="#fn:13"><sup>13</sup></a> as well as less defined <a href="/facts/Tannin/vKIvHoTX">tannins</a> and <a href="/facts/Resin/r1uVThQ8">resin</a>. </p><p><a href="/facts/Hops/mBRf6xGx">Hops</a> are unique for containing <a href="/facts/Secondary_metabolite/mKnQjBQp">secondary metabolites</a>, <a href="/facts/Flavonoid/J7FEAtLE">flavonoids</a>, <a href="/facts/Oil/fsgX2IRM">oils</a>, and <a href="/facts/Polyphenol/H6Q7QIQH">polyphenols</a> that impact the flavor of the products they are common in, such as <a href="/facts/Beer/t7qAGDfj">beer</a>.<a class="footnote-ref" id="fnref:14" href="#fn:14"><sup>14</sup></a> The bitter flavors in hops can be accounted for by acids composed of <a href="/facts/Prenylation/M8owTu4H">prenylated</a> <a href="/facts/Polyketide/94pDr3fm">polyketides</a> (a group of secondary metabolites), which highly impact the taste of hop-based products.<a class="footnote-ref" id="fnref:15" href="#fn:15"><sup>15</sup></a> Multiple genes have been identified as factors in the expression of taste including <a href="/facts/Catechol-O-methyltransferase/GlKMEABG">O-methyltransferase 1</a>, geranyl diphosphate <a href="/facts/Synthase/39C9l6fN">synthase</a>, and <a href="/facts/Chalcone/qtxRtrqA">chalcone</a> synthase. <a href="/facts/Genomic/pVU3BGpL">Genomic</a> analyses have shown evidence that the intervention of humans in the selection process of the hop over the thousands of years it has been cultivated have provided noticeable enhancements in aroma and bitterness as well as selection of varieties with high yield rates.<a class="footnote-ref" id="fnref:16" href="#fn:16"><sup>16</sup></a> </p> <h4>Flowering, growth, and stress response</h4> <p>Predicted genes in <a href="/facts/Homologous_chromosome/hktsBhyx">homologous</a> primary contigs have been identified as accounting for various traits <a href="/facts/Gene_expression/alCPohLR">expressed</a> via variation in the growth, flowering, and stress responses in the plant. These homologous primary contigs correspond to regions with large amounts of <a href="/facts/Sequence_homology/mCIVStrA">sequence variation</a>. <a href="/facts/Gene/e1swwPY6">Genes</a> in the hop that contain higher rates of <a href="/facts/Sequence_homology/mCIVStrA">sequence divergence</a> in homologous primary contigs (overlapping <a href="/facts/DNA_sequences/qAf4kTee">DNA sequences</a> inherited by a common ancestor) have been attributed to the expression of flowering, growth and responses to (both <a href="/facts/Abiotic_stress/pGeXIBDU">abiotic</a> and <a href="/facts/Biotic_stress/AhDWwTlC">biotic</a>) stress in the plant. The responses to stress are thought to manifest in the distinct differences and difficulties in the cultivation processes between geographically popular varieties of the hop plant.<a class="footnote-ref" id="fnref:17" href="#fn:17"><sup>17</sup></a> Outside environmental stress, such as changes in temperature and water availability has also been shown to significantly alter the <a href="/facts/Transcriptome/h6CC0sR5">transcriptome</a> and incite reductions in genes known to be involved in the synthesis of <a href="/facts/Secondary_metabolite/mKnQjBQp">secondary metabolites</a> (including bitter acids), which are <a href="/facts/Organic_compound/gqCNaN45">organic compounds</a> produced that do not impact development or reproduction of hops. Environmental stress has also been shown to reduce <a href="/facts/Gene_expression/alCPohLR">expression</a> of the <a href="/facts/Valerophenone/R5AX9bDS">valerophenone</a> <a href="/facts/Synthase/39C9l6fN">synthase</a> <a href="/facts/Gene/e1swwPY6">gene</a>, which is known to be an essential genetic component in the regulation of bitter acid production. This shows that impacts of outside stress on <i>H. lupulus</i> likely has a direct implication of the expression of the bitter flavor that remains an essential component of the popularity of the plant.<a class="footnote-ref" id="fnref:18" href="#fn:18"><sup>18</sup></a> </p> <h4>Research</h4> <ul><li><i>Humulus lupulus</i> contains xanthohumol, which is converted by large intestine bacteria into the <a href="/facts/Phytoestrogen/lsLPIK1k">phytoestrogen</a> <a href="/facts/8-prenylnaringenin/Xq8EfH3s">8-prenylnaringenin</a>, which may have a relative binding affinity to <a href="/facts/Estrogen/dPEewnDV">estrogen</a> receptors<a class="footnote-ref" id="fnref:19" href="#fn:19"><sup>19</sup></a> as well as potentiating effects on <a href="/facts/GABAA_receptor/6G4rAGb3">GABAA receptor activity</a><a class="footnote-ref" id="fnref:20" href="#fn:20"><sup>20</sup></a></li> <li><i>Humulus lupulus</i> extract is antimicrobial, an activity which has been exploited in the manufacture of natural deodorant.<a class="footnote-ref" id="fnref:21" href="#fn:21"><sup>21</sup></a></li> <li>Spent <i>H. lupulus</i> extract has also been shown to have <a href="/facts/Antimicrobial/80ECEmvP">antimicrobial</a> and anti-<a href="/facts/Biofilm/zg93x2w4">biofilm</a> activities, raising the possibility this waste product of the brewing industry could be developed for medical applications.<a class="footnote-ref" id="fnref:22" href="#fn:22"><sup>22</sup></a></li> <li>Extracts of the bitter alpha-acids present in <i>H. lupulus</i> have been shown to decrease nocturnal activity, acting as a sleep aide, in certain concentrations.<a class="footnote-ref" id="fnref:23" href="#fn:23"><sup>23</sup></a></li></ul> <p>Because of the growing understanding regarding the hop's overlap in gene structures with <a href="/facts/Cannabidiolic_acid_synthase/zJ9qDE7t">cannabidiolic acid synthase</a>, the precursor structure to <a href="/facts/Cannabidiol/PgnVbNqo">cannabidiol</a>, there is a gap in general understanding about potential unknown compounds and benefits in hops. As the understanding of the health benefits available in cannabidiol increases, there is a growing demand to further investigate the overlap between cannabidiolic acid synthase and <i>H. lupulus</i>.<a class="footnote-ref" id="fnref:24" href="#fn:24"><sup>24</sup></a> </p> <h5>Limitations</h5> <p>The <a href="/facts/Genome/31Sm08JT">genome</a> of <i>H. lupulus</i> is relatively large and has been shown to be a similar size to the <a href="/facts/Human_genome/VTV85pbn">human genome</a>. The complexity of the hop genome has made it difficult to understand and identify unknown genetic properties, however with the growing availability of accessible <a href="/facts/DNA_sequencing/hsPsNCQW">sequencing</a>, there is room for more advanced understanding of the plant.<a class="footnote-ref" id="fnref:25" href="#fn:25"><sup>25</sup></a> Because of the growing concern of <a href="/facts/Climate_change/rEN4BDE7">climate change</a>, and the assumption that there will be an increase of <a href="/facts/Heat_wave/33bJ5jh9">heat waves</a>, it is likely that growing large yields of hops could become more difficult. This could result in changes to the <a href="/facts/Transcriptome/h6CC0sR5">transcriptome</a> of the hop, or result in a decrease of certain varieties, leaving less room for further research.<a class="footnote-ref" id="fnref:26" href="#fn:26"><sup>26</sup></a> </p> <h2 id="taxonomy">Taxonomy</h2> <h3>Relation to <i>Cannabis sativa</i></h3> <p>The hop is within the same family of plants such as <a href="/facts/Hemp/quexqR9M">hemp</a> and <a href="/facts/Cannabis_(drug)/241fYAGD">marijuana</a>, called <a href="/facts/Cannabaceae/DYEfetvL">Cannabaceae</a>.<a class="footnote-ref" id="fnref:27" href="#fn:27"><sup>27</sup></a> The hop plant diverged from <i><a href="/facts/Cannabis_sativa/cCNz7R7T">Cannabis sativa</a></i> over 20 million years ago and has evolved to be three times the physical size.<a class="footnote-ref" id="fnref:28" href="#fn:28"><sup>28</sup></a><a class="footnote-ref" id="fnref:29" href="#fn:29"><sup>29</sup></a><a class="footnote-ref" id="fnref:30" href="#fn:30"><sup>30</sup></a><a class="footnote-ref" id="fnref:31" href="#fn:31"><sup>31</sup></a> The hop and <i>C. sativa</i> are estimated to have approximately a 73% overlap in genomic content.<a class="footnote-ref" id="fnref:32" href="#fn:32"><sup>32</sup></a> The overlap between <a href="/facts/Enzyme/DSI1Fh7y">enzymes</a> includes <a href="/facts/Polyketide/94pDr3fm">polyketide synthases</a> and <a href="/facts/Prenyltransferase/RdXqz47s">prenyltransferases</a>.<a class="footnote-ref" id="fnref:33" href="#fn:33"><sup>33</sup></a> The hop and <i>C. sativa</i> also have significant overlap in the <a href="/facts/Cannabidiolic_acid/9nAlFIR4">cannabidiolic acid</a> synthase gene, which is expressed in the tissues of the leaves in both plants.<a class="footnote-ref" id="fnref:34" href="#fn:34"><sup>34</sup></a> </p> <h3>Varieties</h3> <p>The five varieties of this species (<i>Humulus lupulus</i>) are: </p> <ul><li><i>H. l.</i> var. <i>lupulus</i> – Europe, western Asia</li> <li><i>H. l.</i> var. <i>cordifolius</i> – eastern Asia</li> <li><i>H. l.</i> var. <i>lupuloides</i> (syn. <i>H. americanus</i>) – eastern North America</li> <li><i>H. l.</i> var. <i>neomexicanus</i> – western North American.<a class="footnote-ref" id="fnref:35" href="#fn:35"><sup>35</sup></a></li> <li><i>H. l.</i> var. <i>pubescens</i> – midwestern and eastern North America<a class="footnote-ref" id="fnref:36" href="#fn:36"><sup>36</sup></a><a class="footnote-ref" id="fnref:37" href="#fn:37"><sup>37</sup></a></li></ul> <p>Many <a href="/facts/Cultivar/nfaLJJM3">cultivars</a> are found in the <a href="/facts/List_of_hop_varieties/jhuPPtPg">list of hop varieties</a>. A yellow-leafed ornamental cultivar, <i>Humulus lupulus</i> 'Aureus', is cultivated for garden use. It is also known as golden hop, and holds the <a href="/facts/Royal_Horticultural_Society/QrtXmlUo">Royal Horticultural Society</a>'s <a href="/facts/Award_of_Garden_Merit/zQ4Ya8S6">Award of Garden Merit</a> (AGM).<a class="footnote-ref" id="fnref:38" href="#fn:38"><sup>38</sup></a><a class="footnote-ref" id="fnref:39" href="#fn:39"><sup>39</sup></a> </p> <h3>Etymology</h3> <p>The genus name <i>Humulus</i> is a medieval name that was at some point Latinized after being borrowed from a Germanic source exhibiting the h•m•l consonant cluster, as in Middle Low German <i>homele</i>. </p><p>According to Soviet Iranist <a href="/facts/Vasily_Abaev/4l0JGwWG">Vasily Abaev</a> this could be a word of <a href="/facts/Sarmatian/peXYHqbc">Sarmatian</a> origin which is present in the modern Ossetian language (<a href="/facts/Ossetian_language/a4MHjCtL">Ossetian</a>: Хуымæллæг) and derives from proto-Iranian <i>hauma-arayka</i>, an <i><a href="/facts/Aryans/9qU7xRQ2">Aryan</a> <a href="/facts/Haoma/2hTyTgup">haoma</a></i>.<a class="footnote-ref" id="fnref:40" href="#fn:40"><sup>40</sup></a> </p><p>From Sarmatian dialects this word spread across Eurasia, thus creating a group of related words in Turkic, Finno-Ugric, Slavic and Germanic languages (see <a href="/facts/Russian_language/ETXrTgHV">Russian</a>: хмель, <a href="/facts/Chuvash_language/2pvVW2sT">Chuvash</a> <i>хăмла</i>, <a href="/facts/Finnish_language/lBuEIgs0">Finnish</a> <i>humala</i>, <a href="/facts/Hungarian_language/nt4g0ano">Hungarian</a> <i>komló</i>, <a href="/facts/Mordovian/zcHlo6kH">Mordovian</a> <i>комла</i>, <a href="/facts/Avar_language/Qvu8zJHz">Avar</a> <i>хомеллег</i>). </p><p>The specific epithet <i>lupulus</i> is Latin for "small wolf".<a class="footnote-ref" id="fnref:41" href="#fn:41"><sup>41</sup></a> The name refers to the plant's tendency to strangle other plants, mainly <a href="/facts/Common_osier/lpK4xP5p">osiers</a> or basket willows (<i>Salix viminalis</i>), like a wolf does a sheep.<a class="footnote-ref" id="fnref:42" href="#fn:42"><sup>42</sup></a> Hops could be seen growing over these willows so often that it was named the willow-wolf.<a class="footnote-ref" id="fnref:43" href="#fn:43"><sup>43</sup></a> </p><p>The English word <i>hop</i> is derived from the <a href="/facts/Middle_Dutch/E1h4swn9">Middle Dutch</a> word <i>hoppe</i>, also meaning <i>Humulus lupulus</i>.<a class="footnote-ref" id="fnref:44" href="#fn:44"><sup>44</sup></a> </p> <h2 id="distribution-and-habitat">Distribution and habitat</h2> <p>The plant is <a href="/facts/Native_species/03kpM3rf">native</a> to Europe, western Asia and North America.<a class="footnote-ref" id="fnref:45" href="#fn:45"><sup>45</sup></a> </p><p>It grows best in the latitude range of 38°–51° in full sun with moderate amounts of rainfall.<a class="footnote-ref" id="fnref:46" href="#fn:46"><sup>46</sup></a> </p> <h2 id="ecology">Ecology</h2> <p>The flowers attract <a href="/facts/Butterflies/qlSgwlRx">butterflies</a>,<a class="footnote-ref" id="fnref:47" href="#fn:47"><sup>47</sup></a> amongst other insects. </p> <h3>Animal pests</h3> <ul><li>Damson hop aphid (<i><a href="/facts/Phorodon_humuli/zJRKnSkN">Phorodon humuli</a></i>)</li> <li>Two spotted spider mite (<i><a href="/facts/Tetranychus_urticae/pe9VgVQs">Tetranychus urticae</a></i>)</li> <li>Japanese beetle (<i><a href="/facts/Popillia_japonica/xUKl7WU2">Popillia japonica</a></i>)</li> <li>Comma butterfly (<i><a href="/facts/Polygonia_c-album/A9eAHUmw">Polygonia c-album</a></i>)</li> <li>Pale tussock moth (<i><a href="/facts/Calliteara_pudibunda/DBEeBb5z">Calliteara pudibunda</a></i>)</li> <li>Currant pug moth (<i><a href="/facts/Currant_pug/yfX4ApWo">Eupithecia assimilata</a></i>)</li> <li>Buttoned snout moth (<i><a href="/facts/Hypena_rostralis/98zusJTw">Hypena rostralis</a>)</i></li> <li>Buff ermine moth (<i><a href="/facts/Buff_ermine/zAEDGy3c">Spilosoma lutea</a></i>)</li></ul> <h3>Diseases</h3> <p class="note">Main article: <a href="/facts/List_of_hop_diseases/wEELlmp6">List of hop diseases</a></p> <ul><li><a href="/facts/Downy_mildew/IDpEbpdQ">Downy mildew</a> (<i><a href="/facts/Pseudoperonospora_humuli/WXj8tsP9">Pseudoperonospora humuli</a></i>)</li> <li><a href="/facts/Powdery_mildew/qAl00hYE">Powdery mildew</a> (<i><a href="/facts/Podosphaera_macularis/pnUVzCEx">Podosphaera macularis</a></i>)</li></ul> <h2 id="toxicity">Toxicity</h2> <p><i>H. lupulus</i> can cause dermatitis to some who handle them. It is estimated that about 1 in 30 people are affected by this.<a class="footnote-ref" id="fnref:48" href="#fn:48"><sup>48</sup></a> </p> <h2 id="uses">Uses</h2> <h3>In alcohol brewing</h3> <p class="note">Main article: <a href="/facts/Hops/mBRf6xGx">Hops</a></p> <p><i>H. lupulus</i> is first mentioned in 768 CE when <a href="/facts/Pepin_the_Short/oKJwXb04">King Pepin</a> donated hops to a monastery in Paris. Cultivation was first recorded in 859 CE, in documents from a monastery in <a href="/facts/Freising/Wh0EEFea">Freising</a>, Germany.<a class="footnote-ref" id="fnref:49" href="#fn:49"><sup>49</sup></a> </p><p>The chemical compounds found in <i>H. lupulus</i> are the main components in flavoring and bittering beer. The fragrant flower cones, known as hops, impart a bitter flavor and also have aromatic and preservative qualities.<a class="footnote-ref" id="fnref:50" href="#fn:50"><sup>50</sup></a> Some other compounds help with creating foam in beer. Chemicals such as <a href="/facts/Linalool/abBM1jXB">linalool</a> and <a href="/facts/Aldehyde/xSIRkW03">aldehydes</a> contribute to the flavor of beer. The main components of bitterness in beer are <a href="/facts/Alpha_acid/x46PDFYf">iso-alpha acids</a>, with many other compounds contributing to beer's overall bitterness.<a class="footnote-ref" id="fnref:51" href="#fn:51"><sup>51</sup></a> Until the Middle Ages, many varieties of plant were used to flavor beer, including most commonly <i><a href="/facts/Myrica_gale/G4X9QuCF">Myrica gale</a></i>.<a class="footnote-ref" id="fnref:52" href="#fn:52"><sup>52</sup></a> <i>H. lupulus</i> became favored because it contains preserving agents which prolong the viability of a brew. </p> <h3>Outside alcohol production</h3> <p>Buds or hops of <i>Humulus lupulus</i> are used in Iranian ethnomedicine as a <a href="/facts/Sedative/JWzvq66P">sedative</a>.<a class="footnote-ref" id="fnref:53" href="#fn:53"><sup>53</sup></a> </p> <h2 id="in-culture">In culture</h2> <p><i>H. lupulus</i> was voted the <a href="/facts/County_flowers_of_the_United_Kingdom/Vwzdm64C">county flower</a> of <a href="/facts/Kent/aYfQI6Fc">Kent</a> in 2002 following a poll by the wild flora conservation charity <a href="/facts/Plantlife/NLfGu72E">Plantlife</a>.<a class="footnote-ref" id="fnref:54" href="#fn:54"><sup>54</sup></a> </p> <h3>Bibliography</h3> <ul><li>"Czech hop varieties". Žatec: Chmelařský institut, 2012. <a href="http://www.chizatec.cz/download/page5021.pdf">on-line</a></li> <li>Barchet, Ron. "German hops in craft brewing". Wolnzach: Hopfen-Rundschau, 2014.</li> <li>Biendl, Martin. "Hops and health". Wolnzach: German Hop Museum, 2013.</li> <li>Hieronymus, Stan. "For the love of hops: The practical guide to aroma, bitterness and the culture of hops". Boulder, CO: Brewers Publications, a division of the Brewers Association, 2012.</li> <li>Kopp, Sylvia. "Barley & hops: The craft beer book". Berlin: Gestalten, 2014.</li> <li>Melnychuk, M. D.; Boyko, A. L.; Hryhoryuk, I. P.; Likhanov, A. F.; Klyuvadenko, A. A.; Martyn, H. H.; Kukovenko, V. I. "Hop (<i>Humulus lupulus</i> L.): From cell to plant". Kyiv: Printeko, 2013.</li> <li>Nesvadba, Vladimír. "Development and tradition of Czech hop varietes". Žatec: Hop Research Institute, 2013.</li> <li>Neve, Ray A. "Hops". London: Chapman and Hall, 1991.</li> <li>Skomra, Urszula. "Polish hop cultivars". Puławy: Institute of Soil Science and Plant Cultivation, 2010.</li></ul> <h2 id="external-links">External links</h2> Wikimedia Commons has media related to Humulus lupulus. <ul><li><a href="https://hort.purdue.edu/newcrop/duke_energy/Humulus_lupulus.html">Purdue University article</a></li> <li><a href="http://www.botanical.com/botanical/mgmh/h/hops--32.html">Botanical.com - a wealth of information on the Hop plant and its past and modern uses</a></li> <li><a href="http://www.armeniapedia.org/index.php?title=Humulus_lupulus">Armeniapedia.org - Medicinal uses of hops in Armenia</a></li> <li>2005-10-25 Oregon State University <i><a href="https://web.archive.org/web/20070121185641/http://oregonstate.edu/dept/ncs/newsarch/2005/Oct05/beerandcancer.htm">Anti-cancer Compound in Beer Gaining Interest</a></i></li></ul> <h2 id="references">References</h2> <ol> <li id="fn:1"><p>Sewalish, Andrew. "Habitat & Adaptation". Humulus lupulus profile. Retrieved 2017-04-13. <a href="http://bioweb.uwlax.edu/bio203/s2009/sewalish_andr/humulus%20lupulus%20-%20common%20hops/Habitat%20&%20Adaptation.html" target="_blank">http://bioweb.uwlax.edu/bio203/s2009/sewalish_andr/humulus%20lupulus%20-%20common%20hops/Habitat%20&%20Adaptation.html</a> <a href="#fnref:1" class="footnote-back-ref">↩</a></p></li> <li id="fn:2"><p>Sewalish, Andrew. "Habitat & Adaptation". Humulus lupulus profile. Retrieved 2017-04-13. <a href="http://bioweb.uwlax.edu/bio203/s2009/sewalish_andr/humulus%20lupulus%20-%20common%20hops/Habitat%20&%20Adaptation.html" target="_blank">http://bioweb.uwlax.edu/bio203/s2009/sewalish_andr/humulus%20lupulus%20-%20common%20hops/Habitat%20&%20Adaptation.html</a> <a href="#fnref:2" class="footnote-back-ref">↩</a></p></li> <li id="fn:3"><p>Conway, Sean; Snyder, Reid (2008). "Humulus lupulus - Hops" (PDF). College Seminar 235 Food for Thought: The Science, Culture, & Politics of Food. Hamilton College. Retrieved July 31, 2008. <a href="http://academics.hamilton.edu/foodforthought/Our_Research_files/hops.pdf" target="_blank">http://academics.hamilton.edu/foodforthought/Our_Research_files/hops.pdf</a> <a href="#fnref:3" class="footnote-back-ref">↩</a></p></li> <li id="fn:4"><p>"Humulus lupulus (common hop, hops)". Go Botany. New England Wildflower Society. Retrieved 2017-04-13. <a href="https://gobotany.nativeplanttrust.org/species/Humulus/lupulus/" target="_blank">https://gobotany.nativeplanttrust.org/species/Humulus/lupulus/</a> <a href="#fnref:4" class="footnote-back-ref">↩</a></p></li> <li id="fn:5"><p>"HerbalGram: Hops (Humulus lupulus): A Review of its Historic and Medicinal Uses". cms.herbalgram.org. 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