Plants are masterful problem-solvers because they must adjust to their environment in place. Unlike animals, they can’t simply move to a new location if they are hot, thirsty or under threat from predation. As a result, plants have evolved fascinating physical and chemical defenses that help them survive an array of stressors from which they cannot escape. </p> Chemical defenses against insect herbivory are extremely important to plant survival. Insect herbivory damages leaves, hobbling a plant’s ability to photosynthesize and leading to poor seed set, which lowers plant fitness (reproductive success in a given environment). Herbivores can therefore exert strong selection pressure on plants and have spurred a dazzling evolutionary radiation of chemical compounds to problem solve against a menagerie of chewing, rasping and sucking critters.</p> </picture> </div> </div> </article> </picture> </div> </div> </article> Generalist grasshoppers feeding on Verbascum thapsus</em> (common mullein) growing in its introduced range (Montana). Photo: Chrissy Alba</p> Different plant families often harbor specific suites of herbivore-deterrent compounds. For example, one of our locally common members of the Scrophulariaceae, Verbascum thapsus</em> (common mullein), defends itself against herbivores using iridoid glycosides. Common mullein was introduced to North America in the early 1600s by western European settlers who valued it for its medicinal qualities. This situation leads to an interesting question: If herbivores shape the evolution and expression of defensive chemicals, and introduction to a new range vastly shifts the herbivore community, can plants evolve their defenses to better match their new environment? </p> Research has revealed the answer to be yes! The large and diverse herbivore community that fed on mullein in its native range was reduced to a few types of herbivores in its introduced range. Importantly, mostly grasshoppers, which are generalist (wide host range) chewing herbivores, feed on mullein in North America. In Europe, not only generalists, but also a plethora of specialists, which feed specifically on Verbascum </em>or closely related iridoid-containing plants, feed on mullein. Now here’s the twist: the same chemicals that deter generalists like grasshoppers, actually attract </em>a range of co-evolved specialists, like weevils and moth caterpillars, as cues for feeding and egg-laying. This situation is called an “evolutionary dilemma.” What’s a plant to do when defense against one type of herbivore attracts another? </p> </picture> </div> </div> </article> </picture> </div> </div> </article> </picture> </div> </div> </article> Specialist Nothris verbascella</em> (clay groundling moth) caterpillars causing severe damage to young leaves of Verbascum thapsus</em> in its native range (Prague, Czech Republic). Photo: Chrissy Alba</p> By quantifying plant defense profiles of common mullein plants from both the native and introduced ranges, several colleagues and I (over years, with lots of fieldwork and experiments!) found that introduced mullein plants have evolved since being introduced to North America, exhibiting higher levels of chemical defense against generalist herbivores (those pesky grasshoppers!) than their native counterparts. Introduced mullein was freed from the evolutionary dilemma of deploying iridoid glycosides at some evolutionarily tuned “sweet spot” that could defend against generalists while not being overly attractive to specialists. </p> If you thought that our evolutionary story ended there, keep your seatbelts on! Investing in defense is not free – it costs plants in energy and resources. So, one last trick of genius is that the ramped-up levels of defense found in introduced mullein is concentrated in the plants’ young leaves. Young leaves are more valuable to defend because they are generally higher in nitrogen, more highly photosynthetic, and hold more water than older leaves. Losing them to herbivores is therefore costly. This is an optimal deployment of defense because the overall amount of defense is similar at the whole-plant scale, it’s just more optimally distributed among different plant tissues. And there you have it: right in your backyard, mullein has evolved within a few hundred years to better match its new herbivore environment. Problem-solving at its finest. </p>
The art collection at Denver Botanic Gardens is now publicly accessible via the PastPerfect database! Discover more than 800 beautiful and curious artworks just waiting to be browsed. While exploring the art collection, take note of the impressive number of artworks by significant female botanical artists in Colorado including Anne Ophelia Dowden, Emma Armstrong Ervin and Irene Jerome Hood. </p> One of my favorite artists in the collection is undoubtedly Irene Jerome Hood (1858-1945). Hood was a renowned artist and photographer active in the Victorian era. She grew up in Ellicottville, New York. Hood and her husband moved to Colorado in 1892 and the artist spent a lot of time creating artwork in and around her Denver home. Hood’s accomplishments include four books of nature photography, an exhibition of sketches of Colorado scenery and illustrations for a book by Enos Mills about Estes Park. Our art collection contains 162 of her watercolor paintings. </p> These artworks are of interest to Coloradans and those fond of the wonderful geographic diversity of the state. Hood depicts remote and pristine mountain vistas as well as iconic Colorado urban locales including beloved public parks. While we’re in these winter months, Hood’s paintings of Washington Park from summer and fall ignite a nostalgia for these color-filled months of brilliant blooms and foliage. </p> </p> </picture> </div> </div> </article> Irene Jerome Hood, Washington Park Pink 1922</em>, watercolor, 1922. </p> </picture> </div> </div> </article> Irene Jerome Hood, Washington Park October 2</em>, watercolor, ca. 1928. </p> Another notable quality of Hood’s watercolors is the originality of her compositions. In several watercolors Hood opts for a more artistic context for her botanicals, diverging from the traditional scientific style of botanical illustration. In Bryant Anemones</em>, Hood adds interest to her watercolor by creating optical illusions in paint; Hood creates a crack that appears to be three dimensional and then makes it appear as if the flower on the right is arranged in a slit in the paper. </p> </p> </picture> </div> </div> </article> Irene Jerome Hood, Bryant Anemones</em>, watercolor, 1883. </p> Hood also married art and poetry within many of her botanical works. One of Hood’s watercolors prominently features William Wordsworth’s famous 1804 poem "I Wandered Lonely as a Cloud." Hood combines manuscript lettering with a small waterscape and yellow daffodils bringing her artwork to life with the poetry of William Wordsworth. </p> </picture> </div> </div> </article> Irene Jerome Hood, I Wandered Lonely as a Cloud</em>, watercolor, date unknown. </p> Irene Jerome Hood had a unique penchant for infusing her artwork with personality and conveying to viewers the beauty of the natural world in her expertly rendered watercolors. To learn more about the art collections and to view more works by Irene Jerome Hood, visit the Gardens’ online art collections database</a>. </p> </p> This post was written by Art Collections Assistant Megan Adams.</em></p>
Scattered about the Gardens are winter displays that celebrate our passion for plants. Many are in homage to summer beds; others showcase the changing textures and colors of fall. All speak to our love of plants in all their stages – and test the limits of displaying dried plants outdoors.</p> In keeping with our mission to be sustainable, the displays are 99 percent compostable. We only use air-dried and fresh plant material, or cuttings soaked in vegetable glycerin. The wire used in wreaths is reused, as are the armatures and foraged pinecones.</p> We begin the tour before we cross York Street from the parking garage</strong>. By the crosswalk, garlands of Limonium binervosum</em> (rock sea lavender), Seseli gummiferum</em> (moon carrot) and Dipsacus laciniatus </em>(dyed with Aronia</em> berries) ring the insides of pots and seed heads of Allium schubertii </em>(ornamental onion) rise on bamboo poles.</li> Crossing the street to the left, a giant nest hovers above a container on bamboo stilts. The nest is woven from Salix matsudana</em> ‘Snake’ and trimmed with dried flowers. Inside, a family of bottle gourd birds nestles in a bed of Miscanthus sinensis</em> and Eupatorium capillifolium </em>‘Elegant Feather’.</li> Straight ahead at the Bonfils-Stanton Visitor Center</strong> entrance, towers of maple branches are adorned with giant blooms built to resist the wettest snow. The petals are the fibrous pods of Asclepias speciosa</em> (showy milkweed) and the centers, Echinacea </em>(coneflower) seed heads. Encircling the towers are clouds of dried Limonium latifolium</em> (sea lavender).</li> Entering the Gardens, turn left into the Welcome Garden</strong> and upstairs to a bear made of alder twigs. The twigs are woven around a topiary and the eyes painted on slices of branch. In the left paw is a bamboo wand topped with an allium seed head.</li> Ahead at the gate to the Secret Passage </strong>hangs a wreath wired with dried flowers and pods – Tanacetum vulgare</em>, Dahlia</em> ‘Summit Festival’ and Nigella</em> ‘Albion Black Pod’ (love-in-a-mist) hint at the intensifying colors of the dogwoods and willows inside. </li> Take the winding path past willow cages and birch nests and enter the Romantic Gardens</strong> where grand bouquets of Sorghum bicolor </em>(broom corn), Hydrangea</em> and more fill out pots. Each year the Garden Club of Denver descends like a flock of birds and decorates a dozen containers.</li> Next head to Woodland Mosaic</strong> where dried plants are mixed with fresh. Taupe wands of Miscanthus</em> rise from pots and create the backdrop for fresh clusters of red roses, as dried flowers of Hydrangea</em> and Sedum</em> cascade below freshly cut Berberis aquifolium</em> (Oregon grape).</li> Then on to South African Plaza</strong> to see evergreens mixed with generous bunches of Salix geyeriana </em>(Geyer’s willow) and Salix monticola </em>(mountain willow), their tawny bark seeming to glow even on grey days. Foraged cones fill a pot between them and pansies bloom in the reflective warmth of a concrete wall.</li> Head north to the Victorian Secret Garden</strong>, where a spiraling Juniperus chinensis</em> ‘Spartan’ rises at the entry. Inside the gazebo, a fountain of Sorghum bicolor rises above a pot and palm fronds and Symphoricarpos </em>(snowberry) berries encircle a container of branches pierced with clear globes.</li> Then it’s on to the entrance of Marnie’s Pavilion</strong>, where a container display glows tan and rose. Stalks of Eremurus</em> (foxtail lily), Miscanthus</em> and more rise above shifting shades of Celosia argentea</em> var. cristata</em> ‘Tornado Red’. Creamy balls of Hydrangea arborescens</em> ‘Annabelle’ add pop and tresses of Amaranthus caudatus</em> tumble over the pot’s edge.</li> The last stop is past the Crossroads Garden </strong>along the benches. There, advent wreaths made of Cornus sericea</em> ‘Baileyi’ float on bamboo poles. Each wreath is adorned with willow “candle sticks” and Lunaria annua </em>(money plant) “flames.” Tucked into the wreaths are dried Nymphaea </em>(water lily) blooms, Nelumbo nucifera</em> (lotus) seed heads, and Bupleurum </em>flowers.</li> </ul>
