Lichens Are Awsome, And So Can You

    Before I post about any lichens in particular, I want to put a sort of "lichen basics" guide out there to give people a point of reference. Lichens are a fascinating set of organisms that live virtually everywhere and are oft overlooked because of their small size and low profile. There are many advantages to enjoying learning about lichens:

1. They live on every rock, tree, and forest floor in every habitat during every season. Lichens are remarkably resilient, adapted to living on bare rock surfaces that bake in full summer heat before freezing in winter cold, year after year. 
2. Many lichens are readily identifiable to the genus level by their outward appearance with a hand lens, even if plenty do require a microscope to identify on the species level. 
3. Lichens provide a range of fantastic colors and shapes not seen in plants or fungi separately.
4. Many lichens have a cosmopolitan distribution, with favorites such as Rhizocarpon geographicum growing in the Rockies as well as the Himalayas. This means that a travel enthusiast can be comforted in the knowledge that their favorite simple symbionts are always keeping them company. 

Virtually any rock surface in Colorado. Many rocks are so covered in lichens that 

their original color is not apparent. This was Pike's Peak granite, which is a rosy-pink 

color, covered in a plethora of grey and green lichens. 

     The terminology surrounding lichen identification is not particularly hard to learn, but it is idiosyncratic to the point of being arcane. On top of this, many lichens lack a colloquial name as nobody but lichenologists has payed them much heed over the years. This makes lichen literature tricky to access, as the written word describing the lichens can actually become an impediment to understanding them. My hope with this post is to lay out the basics of what someone needs to appreciate the stunted, crusty world of lichens in a casual way. 

Lichen Basics 

      First off, it is good to establish that lichens are neither a plant nor a fungus, but a sort of combination of both. The bulk of the organism that is visible to the naked eye is the fungal body of the lichen, typically an ascomycete. The fungal symbiont lives in relationship with a photosymbiont (a symbiotic organism capable of photosynthesis), which is either an alga or a cyanobacterium, or rarely both (1). The anatomy within the lichen where these organisms interact is microscopic, and a good description can be found on this Wikipedia page. A quick field test for which photosymbiont you are dealing with is to simply wet the lichen. This renders the upper layers of the lichen's cortex transparent, allowing the color of the photosymbiont to show through. A light to forest green indicates an alga (see below), while darker, almost black coloration indicates a cyanobacterium. This test does not work on lichens with strongly pigmented coloration. Note that a lichen's binomial (scientific) name is always the name of the host fungal organism, which may live in symbiosis with a variety of algae or bacteria. 

Xanthoria fallax, a common lichen on tree bark in urban areas. Note the difference between the dry sample (left) 

and the same sample when wet (right). The light green color indicates an algal symbiont for this species. The 

black marks in the left image are millimeters.

    The relationship between the fungal body, which provides habitat, and the photosymbiont, which provides food, allows lichens to colonize environments such as desert rock faces which would be lethal to virtually any other living thing. Part of lichen's ability to colonize these surfaces apparently involves their ability to dry completely, and then revive again once water becomes available (2). 

Lichen Morphology 

     Lichens are broadly classified by the characteristics of their fungal body, or thallus (yes, with a "th"). There are several categories of lichen body based on macroscopic features, but for the purposes of getting by it is sufficient to know about crustose, foliose, and fruticose lichens. 

Crustose Lichens 

     A crustose lichen's thallus is tightly attached to the surface it is growing on, which is frequently stone. Crustose lichens tend to be fairly simple, with three main structures that are of interest (see illustration below).

A typical crustose lichen. Note the circular growth pattern of the thallus. 

1. Apothecia: (singular apothecium) reproductive structures of lichens where spores are formed and disseminated. On crustose lichens they may be a variety of shapes, but are typically cup or wart-shaped. In many cases they are easy to pick out from the thallus surface because they are a different color, different shape, or both. 
2. Thallus: the "body" of the lichen where photosynthesis and growth occur. In a crustose lichen the thallus may be warty (as above), wavy, or grainy, but it is always fused to the substrate it is growing on. 
3. Margin: the growing edge of the lichen, where the fungus has gotten ahead of the photosymbiont. This structure is not present in all or even most crustose lichens, but it is a handy fieldmark when you can find it. It is frequently a different color from the thallus, but not always. The margin tends to be flatter than the thallus, and less textured.  

Lecidea tessellata, a familiar crustose lichen seen here growing on Mount Evans next to an 

unidentified foliose lichen. Note the black apothecia and gray, tile-like thallus. 

Lecidea atrobrunnea (brown and black) and Rhizocarpon geographicum (yellow-green with black spots)

growing on quartz. These species tend to grow together. Note the well-developed black margins of the thalli.

A violently orange crustose lichen, probably Xanthoria elegans, growing on gravely soil 

at near 14,000ft on Mount Evans. The apothecia in this species are much more disc-shaped 

and are so numerous that the thallus is hardly visible in this photo. 

Foliose Lichens 

     Foliose lichens are so-named because their thalli grow in creeping leaf-like structures over the surfaces they cover. The thallus tends to be attached either at a central point, referred to as an umbilicus, or to have several small attachments at the base of each "leaf" as the lichen grows. See illustration below: 

A composite illustration of features of foliose lichens. This illustration is not based 

on a particular species and shows features that may occur.

1. Apothecia: serve the same function in foliose lichens as in crustose. In foliose lichens the more cup-shaped apothecia seem to predominate, although the more wart or bump-shaped ones are also found. Note the rounded edges present in the image above. These are referred to as the margin of the apothecia, and the margin's presence or absence, shape, and color are all useful field marks. 
2. Thallus: again, the body of the lichen. The curling "leaves" that spread from the center of the lichen are referred to as lobes. 
3. Rhizines: root-like structures that a lichen may use to anchor itself to a surface. To my knowledge rhizines only serve as anchors, and do not perform nutrient uptake as they might in a plant. Rhizines are actually bundles of mycelium, so the analogy to roots is somewhat strained. 
4. Isidia and Soredia: sporulating structures that make the thallus look crusty or dusty. I've included them here together because they are difficult to differentiate without a decent amount of magnification, so number 4 in the illustration could reasonably be either. Isidea are small, horn-like protrusions from the thallus surface that contain photobionts and may break off to start new lichens (3). Soredia are hyphae-jacketed photobionts that erupt from the thallus in various places. A site where this is happening in a cluster is called a soralium. The goal of both structures is reproduction.
5. Pycnidia and Parithecia: sunken sporulating structures each of which consists of an urn-like structure in the thallus which releases spores through a small opening. There are some functional and structural differences between the two, but these are not really visible without a microscope. To the casual lichen lover, both structures appear as sunken black pores studding the surface of the thallus.   

Rhizoplaca chrysoleuca, a common foliose lichen. Note the lobed 

thalli and the bright orange apothecia with gray margins.

Vulpicida pinastri, sporting bright yellow soredia. At the scale of this  photograph it would be 

difficult to distinguish soredia from isidia. The tentacle-like lichen in the background is in the genus Cladonia. 

Fruticose Lichens 

  
     I opted not to do an illustration for fruticose lichens, as they come in a bewildering array of shapes. Fruticose lichens maintain a three-dimensional structure by wrapping the medulla in cortex the whole way around. This allows for the growth of bizarre cup shapes, horns, filaments, and all kinds of other variations. Fruticose lichens may have any of the structures present in foliose lichens, but their main identifying trait tends to be the overall shape of the thallus. I have included some pictures below to help give an idea of the diversity of fruticose lichens. 

Stereocaulon tomentosum growing on the damp forest floor near Pike's Peak. Note the 

upright habit. The maroon blobs are apothecia. Large patches of this lichen can 

look like unseasonable frost from far away.

Cladonia pyxidata growing on a bed of moss. The orange coloration is not typical. The 

primary thallus is the small, foliose structure at the base, while the much more salient 

secondary thallus is the fruticose cup-shaped structures. The grainy texturing on the cups 

is from masses of isidia. 

Small tufts of a lichen in the genus Usnea, likely U. lapponica,  adorn deadwood on Mount Evans. Usnea 

species all look quite similar and may be found draped from deadwood on conifer trees throughout the state.

 A higher magnification of the thallus reveals the studded thallus and branching habit. I have not been able to figure out the function of the black spots, which are neither apothecia nor pycnidia. 

Bryoria fuscescens, a.k.a. horsehair lichen, growing with somethingorother foliose 

on dead wood. In the interest of science, a photo of someone wearing B. fuscescens as a 

beard may be found here. 

A magnification of  B. fuscescens. The white disc-like structures which I 

originally mistook for apothecia are actually soralia, with the white 

medulla showing through where the cortex has ruptured. 

Other Morphological Subtypes 

     The subtypes I have chosen not to address are relatively uncommon compared to the main three types listed above. These can be helpful, but I have found that at least in Colorado it is mostly possible to get by without them. Squamulose lichens have thalli that are composed of interlinking scales (squamules) which, like crustose lichens, lack a lower cortex (4). However, as in foliose lichens, the scales may lift above the surface the thallus is growing on. Leprose lichens lack the layered cell structure present in other lichens, and the thallus simply consists of powdery-looking granules. There are even more subtypes listed on the page I have linked to and in other sources. 

Going Out into the Wild World of Lichens 

     The first step in appreciating lichens is simply to recognize them in your environment, which may be enough for most people. Next time you are on a walk in nature, slow down by a tree or a rock surface and look closely at the great variety of shapes and colors blossoming on a tiny scale in front of you. If you want to try to identify actual genera or species, I recommend picking up a simple hand lens and an illustrated guide. 
     Unfortunately, good guides for the budding (or sporulating) amateur lichenologist are hard to come by. A Rocky Mountain Lichen Primer, by Corbridge and Weber, is a good guide for Rocky Mountain lichens which was written with an amateur in mind. This is probably good, since this is the only compiled guide to lichens in the Rocky Mountains in particular that I have been able to find. The Consortium of North American Lichen Herbaria (CNALH) has online hosting of impressively exhaustive lists of lichen species present in different locations around Colorado, complete with photos and descriptive information, which may be accessed here. 

     Finally, in a fit of graduate school-induced, hyperfocused, work-avoiding behavior, I curated information and photographs for about 150 lichen species based on this list of lichens seen in Rocky Mountain National Park. This was based on the assumption that the lichen flora of RMNP would be fairly representative of the lichens that live in the state at large. The list, which should have mostly correct citations for all print sources, may be viewed and downloaded here in .pdf format (large file warning). I did not take the time to cite all my photo sources: all photos are intellectual property of whomever took them originally. Please do not sue a poor amateur lichen enthusiast, thank you. All species are organized in alphabetical order by binomial name with photos on the first slide and information on the second. The backgrounds of the slides are colored and categorized by color to reflect my perception of the lichen's thallus color to improve ease of browsing. I apologize if the colors seem off: there are many variations within lichens between beige, brown, tan, gray, grey, green, green-gray etc. which can easily be interpreted one way or another.  

    I hope you have enjoyed learning about the bizarre world of lichens. I will reference this post periodically as I post specifically about given lichen species, and I encourage those of you who are interested to come on back and review your terminology here. If you take a few minutes to do so, you are taking your first steps into a smaller world! Thanks for reading. 

References

1. Corbridge, J. N., & Weber, W. A. (1998). A Colorado Lichen Primer. Niwot, CO: University Press of Colorado.
2. Lichens: Life History and Ecology (n.d.) Retrieved from http://www.ucmp.berkeley.edu/fungi/lichens/lichenlh.html
3. The Difference Between Isidea and Soredia (n.d.) Retrieved from http://www.plantscience4u.com/2014/07/difference-between-isidia-and-soredia.html#.VjAv3berTIU
4. Images of British Lichens (n.d.). Retrieved from http://www.lichens.lastdragon.org/faq/lichenthallustypes.html#squamulose

Front Range Nightshades

      The nightshades (family Solanaceae) comprise a fairly small number of species in the Rocky Mountain Region. One guidebook I frequently use only cites three species(1), while this handy site(2) only offers five. I've chosen to look more closely at our native nightshades for this post because they tend to be distinctive-looking, have an interesting history of use by humans, and to have effects on other commercially important nightshade species(3). This post is not a comprehensive list of our local nightshades, but highlights some of the most salient ones I have encountered in the front range area.

     While the nightshades do not make up a large percentage of locally occurring species, many of the most beloved garden plants we all use on a year-to-year basis are nightshades. These include potatoes, tomatoes, petunias, peppers, daturas, and tomatillos. Those which are not edible tend to be poisonous, and those which are edible often have poisonous look-alikes which grow in the wild. One of the most famous nightshades is the infamous Atropa belladonna, erstwhile known as deadly nightshade, which derives its name from the Italian "beautiful woman" (bella donna) in reference to the ability of the atropine contained in its leaves to dilate the pupils of women to fetching proportions(4). 

     The three species of nightshade which I have seen growing in the foothills region of Colorado are neither as deadly nor as useful as any of the aforementioned species, but they all have their own quirks which make them interesting in their own rights. 

Hyoscyamus niger, Common Henbane, Black Henbane

H. niger growing on North Table Mountain in full sun near Golden.

General Information 

     Henbane's name is difficult to pin down, etymologically. One source(5) published recently in the peer-reviewed literature cites a paper which intuitively states that it's name comes from the Anglo-Saxon for "hen murder," due to hens eating the seeds and suffering neurological symptoms and death. By contrast, Abram Smythe Palmer contended in his exquisitely named Folk Etymology, A Dictionary of Verbal Corruptions or Words Perverted in Form or Meaning, by False Derivation or Mistaken Analogy(6), that it is from the Anglo-Saxon henne-belle meaning "hen bell," possibly corrupted from "henge-belle," which actually means hanging bell. The second explanation is also plausible, as the calyx (see photo) does hang down in a bell-like fashion.

     Whatever you call it, henbane is a common, rapidly spreading plant which is classified as a noxious weed in Colorado(7). It is exotic to our state, originating in Eurasia. It has pubescent stems and leaves. The leaves are also coarsely toothed with prominent veins, and reportedly emit a foul odor when damaged, although I have not noticed it. The flowers are yellow-brown with five darker brown or purple splotches more proximal to the center. I find it easy to pick out of a crowd while hiking as its gestalt  is immediately reminiscent of its domesticated cousins the tomatoes.  

Chemistry and Ethnobotany  

     Henbane holds a host of physiologically active alkaloids which have a variety of effects on the body. These include scopolamine, which is the chemical that makes green potatoes poisonous to humans(8). It is not surprising then that most common experience resulting from consuming henbane is acute poisoning via anticholinergic action on the parasympathetic nervous system (9). 

     Henbane has a long and colorful use of medical uses for conditions as varied as sleeplessness, pain, and toothache cures(5). It was used (likely as a hallucinogen) by people attempting to practice witchcraft(5). It was also used as a poison for intrigues, and is conjectured to be the poison used to kill Hamlet's father(10). An much more thorough treatment of henbane through history can be found for free here. 

     Perhaps the most interesting use of henbane was in the brewing of gruits, beers which used herbs other than hops for flavoring(11). Henbane was used as a "flavoring," although the fact that it was psychoactive likely had a bearing on its use as well. Henbane fell out of favor as a beer flavoring with the institution of the Bavarian Purity Laws, although presumably clumsy brewing resulting in poisonings caused some caution prior to that. It is also worth noting that our very own in-state New Belgium Brewing has experimented with making a gruit, although presumably they skipped the H. niger in their recipe. 

Solanum rostratum, Buffalo Bur, Prickly Nightshade 

S. rostratum growing on North Table Mountain near Golden. Note the spines, deeply-lobed leaves, and potato-like flowers. 

General Information

     I have only encountered this interesting plant once on a hike, although to read the literature you would think it is spreading over the West and much of the rest of the world like a great, thorny, carpet. It is a highly invasive species which has found it's way to all continents except Antarctica, as well as New Zealand(12). Here in Colorado, as well as in the great plains region and Mexico, it is actually a native species. It is believed to be most native to Mexico, where the species' greatest genetic diversity occurs. An impressively detailed report on the prevalence of S. rostratum as well as some other interesting information about the species may be found here.

     The name rostratum means in Latin having a curved or hooked beak(13), possibly referring to either the stamens of the flowers or to the plant's copious thorns, which cover the stems and leaves. Other names include beaked nightshade, beaked sandbur, buffalo berry, buffalo bitter apple, buffalo bur, hedgehog bush, horned nightshade, horse nettle, Kansas thistle, pincushion nightshade, sandbur, and spiny nightshade(12). It has pinnatifid leaves and produces pentagonal yellow flowers with five partially-fused or fused petals. The flower produces two different types of stamen, a phenomenon known as heteranthy, and which may allow flowers to more effectively spread pollen for reproductive purposes when a pollinator species uses the pollen as food(14).   

Chemistry, Ethnobotany, and History

     Like other nightshades, S. rostratum is host to a laundry list of substances, at least some of which are poisonous via cholinesterase inhibition(15). Apparently S. rostratum  is potent enough to kill piglets, but I have not been able to find any record of human poisoning. Presumably the plant's hostile demeanor has helped to keep hungry people at bay. 

    Also as with other nightshades, people have used S. rostratum as a medicine. Pre-Columbian people in Mexico used it as a treatment for hypertension(16). Interestingly, studies of rat aortas indicate that S. rostratum extracts can serve as a vasodilator, which supports the therapeutic effectiveness of this plant.

    Probably the most interesting thing about S. rostratum is that it is the original host species for the Colorado potato beetle(17). The Spanish "explorers" helped to spread both S. rostratum and its accompanying beetle outside of their native ranges as they traveled through the Americas. Then came the widespread cultivation in America and abroad of the closely related domestic potato (Solanum tuberosum), which the potato beetle adapted to with ease. As international trade and travel became more prevalent, the Colorado potato beetle ascended from its humble beginnings as a pest on only S. rostratum to its current status as a global scourge on the potato industry. So prevalent and devastating was the spread of the beetle that the Warsaw Pact countries actually accused the Western powers of unleashing the beetle on them as a form of entomological warfare(18). While this is doubtful and likely more for propaganda than anything, it is interesting to think that a beetle adapted to eat only one spiny weed from Mexico has managed to cause so much damage.

Physalis virginiana, Ground Cherry, Virginia Ground Cherry

or

Physalis longifolia, Common Ground Cherry

P. virginiana growing in a neighbor's yard. 

It also inhabits more wild areas than the suburbs. Flowers (not pictured)

are white/beige and look similar to tomatillo or pepper flowers.

General Information

     There is some debate within circles that debate this sort of thing on whether the species present in Colorado represent P. virginiana, P. longifolia, or both(19). Two of Colorado's botanical heavyweights, Weber & Wittman(20), consider the two species to be synonymous, so I will treat both as P. virginiana for the remainder of the post. 
     Plants in the genus Physalis are immediately recognizable by their unusual calyces, which envelope the small green fruits inside like a paper lantern. The tomatillo is one familiar variety of Physalis, as is the wild cape gooseberry. P. virginiana is not edible like those, although it could easily be mistaken for the latter. It could likewise be mistaken for virtually any of the numerous varieties of Physalis that grow in the United States, for that matter, as plants across the genus tend to be quite similar. 
     Fortunately, the other two varieties that grow in Colorado,,P. heterophylla and P. lobata, are easily distinguished by the presence of hairs on their stems and leaves, which P. virginiana lacks. P. virginiana sports lanceolate leaves which may have slightly dentate margins, glabrous stems which may have some purple pigmentation a branching points, and solitary (occasionally in small groups) yellow/beige flowers which are pendant on the stalk and which have a fused to semi-fused corolla of five petals(21). The plant's most striking feature is the papery, enveloping calyx occluding its ripening fruit (see pictures
below). 

P. virginiana fruit as found on the plant (left) and with calyx removed (right). 

The fruit turns a vibrant orange when ripe. 

Chemistry, Ethnobotany, and Economic Importance 

     P virginiana is probably poisonous, but I have been unable to find any references to human or animal poisoning. However, I have found a report that a preparation of P. virginiana was used by some Native Americans as a treatment for eye infections, open wound dressings, and some stomach ailments(22). Researchers who applied an extract of P. virginiana to colonies of pathogenic bacteria found that it inhibited their growth. 
    I find the history of using plants as medicine no end of fascinating, especially in cases such as this where the plant actually proved to be physiologically active for the purpose it was used for. I imagine an inconceivably long process of trial and error to arrive at some of the plant-based remedies that native peoples use for medicine. The anthropologist Wade Davis notes in this TED talk (which I highly recommend) that native people he spoke to take a less systematic approach to these discoveries(23). He says that the people thought of the plants as "talking to them," and that they felt an almost mystical connection to the botanical world around them. At risk of sounding froofy, I would like to say that I still consider the native people's ultimate success in finding plants that worked for them a process of trying things out, but I do imagine that the social and emotional reality of being surrounded and grounded in your botanical environment is very different from what we experience in industrialized nations. 
     The economic significance of P. virginiana is limited, but it does serve two important roles. The first is that of a noxious weed, especially in warmer climates such as California where it is a perennial(21). The second is as a reservoir species for potato virus Y, a virus which can reduce yields or cause necrotic rot on potato plants(24). In other words, while it may be beautiful and interesting, P. virginiana is an unwelcome guest most places it chooses to grow.  

     This concludes my prickly and poisonous exploration of nightshades that grow in the front range. Stay tuned for more fun with flowers, fungus, and lichens (which do not alliterate).  

References 

1. Craighead, J. J., Craighead., F. C., & Davis, R. J. (1963). A Field Guide to Rocky Mountain Wildflowers. Boston, MA: Houghton Mifflin Company.
2. List of Scientific Names (N.D.) http://www.easterncoloradowildflowers.com/
3. LAPP N, A., & GOODING G V, J. (1976). OCCURRENCE AND SOURCES OF INOCULUM OF POTATO VIRUS Y IN TOBACCO IN NORTH-CAROLINA. Plant Disease Reporter, 60(12), 1014-1016.
4. Hofmann, Albert; Schultes, Richard Evans (1987). Plants of the Gods: Origins of Hallucinogenic Use. New York: Van der Marck Editions. p. 88.
5. Alizadeh, A., Moshiri, M., Alizadeh, J., & Balali-Mood, M. (2014). Black henbane and its toxicity - a descriptive review. Avicenna Journal Of Phytomedicine, 4(5), 297-311.
6. Palmer, A. S. (1882). Folk etymology, a dictionary of verbal corruptions or words perverted in form or meaning, by false derivation or mistaken analogy. Chiswick, Tooks Court: Charles Wittingham and Co.
7. Baker, D. V., Steinke, T. L., McDonald, S. K. (N.D.) Black henbane: Hyosciamus niger L. Retrieved from: http://www.gunnison.colostate.edu/agri/weedsb/weed_docs/blackhenbane.pdf
8. Friedman, M. (2004). Analysis of biologically active compounds in potatoes (Solanum tuberosum), tomatoes (Lycopersicon esculentum), and jimson weed (Datura stramonium) seeds. Journal Of Chromatography. A, 1054(1-2), 143-155.
9. Miniksar, Ö. H., Özkan, A. S., Aydoğan, M. S., Yücel, A., & Toğal, T. (2015). Life-Threatening Poisoning Associated with Henbane Plant. Journal Of Turgut Ozal Medical Center, 22(1), 76-77. doi:10.7247/jtomc.2014.2219
10. Kotsias, B. A. (2002). Scopolamine and the murder of king Hamlet. Archives of Otolaryngol Head Neck Surgery, 128(7):847-849. doi:10.1001/archotol.128.7.847.
11. Eul, H. K. (1997). From Pils via henbane beer and aphrodisiac beer to the Beer Purity Law. Brauwelt, 137(51/52), 2323-2325.
12. Center for Agriculture and Biosciences International (CABI)(2015). Solanum Rostratum (prickly nightshade). Retrieved from http://www.cabi.org/isc/datasheet/50544
13. Lewis, C. T. (1891). Elementary Latin Dictionary. Oxford: Oxford University Press.
14. Vallejo-Marín, M., Manson, J. S., Thomson, J. D., & Barrett, S. H. (2009). Division of labour within flowers: heteranthery, a floral strategy to reconcile contrasting pollen fates. Journal Of Evolutionary Biology, 22(4), 828-839. doi:10.1111/j.1420-9101.2009.01693.x
15. Bassett, I. J., & Munro, D. B. (1986). The Biology of Canadian weeds. 78. Solanum carolinense L. and Solanum rostratum Dunal. Canadian Journal of Plant Science, 66, 977-991.
16. Ibarra-Alvarado, C., Rojas, A., Mendoza, S., Bah, M., Gutiérrez, D. M., Hernández-Sandoval, L., & Martínez, M. (2010). Vasoactive and antioxidant activities of plants used in Mexican traditional medicine for the treatment of cardiovascular diseases.Pharmaceutical Biology, 48(7), 732-739. doi:10.3109/13880200903271280
17. Izzo, V., Mercer, N., Armstrong, J., & Chen, Y. (2014). Variation in host usage among geographic populations of Leptinotarsa decemlineata, the Colorado potato beetle. Journal Of Pest Science, 87(4), 597-608. doi:10.1007/s10340-014-0578-2
18. Lockwood, J. A. (2008). Six-Legged Soldiers: Using Insects as Weapons of War. Oxford University Press. p. 136.
19. Open Forum Discussion Group on the Flora of Colorado (N.D.) p 371. Retrieved from http://www.swcoloradowildflowers.com/coloradoflora.htm
20. Weber, W. A., & Wittman, R. C. (2012) Colorado flora: Eastern slope (4th ed.). Boulder, CO: University Press of Colorado
21. California Department of Food and Agriculture (N.D.) Physalis. Retrieved from https://www.cdfa.ca.gov/Plant/IPC/encycloweedia/weedinfo/physalis.htm
22. Gibson, K. A., Reese, R. N., Halaweish, F. T., & Ren, Y. (2012). Isolation and characterization of a bactericidal withanolide from Physalis virginiana. Pharmacognosy Magazine, 8(29), 22-28. doi:10.4103/0973-1296.93307
23. Davis, W. (2007). Dreams from endangered cultures (transcript). Ted Talk. Retrieved from https://www.ted.com/talks/wade_davis_on_endangered_cultures/transcript?language=en
24. LAPP N, A., & GOODING G V, J. (1976). OCCURRENCE AND SOURCES OF INOCULUM OF POTATO VIRUS Y IN TOBACCO IN NORTH-CAROLINA. Plant Disease Reporter, 60(12), 1014-1016.