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Anita’s Blog – What We Don't See

There’s a lot going on in the garden than what mere humans can see.


That’s scary, interesting, disturbing, awkward – take your pick. Before you get too alarmed and grab your camera, or worse, and head out to your garden to scour the bushes for nefarious activity, I’m only talking about nectar guides.


First a little fun with words. According to my favorite plant terminology book: *

Nectar is a sugary, sticky fluid secreted by many plants.

Nectary is a tissue or organ which produces nectar.

Nectariferous means with nectar.

Nectar guides are lines or spots, often invisible except in ultraviolet light, directing pollinators toward the nectaries.


It's all about rewards, the rewards being nectar and pollen. Nectar is the most common floral reward. Critters that use nectar guides are called flower-visitors. Visitors might be flies, bees, bats, birds, butterflies and other nectivorous insects.


Nectar is composed chiefly of carbohydrates and water, with low levels of amino acids, lipids, proteins, and various vitamins and minerals. It is this sugar-rich food source that fuels adult bees, butterflies, and a myriad of other flower visitors, such as bats and hummingbirds.


"Pollen, the most protein-rich of these rewards, is essential to bee reproduction. Once gathered, adult bees typically mix pollen with nectar and glandular secretions to form a nutritious “bee bread,” which forms the diet of larval bees.” https://www.storey.com/article/how-flowers-bees-evolved/


Nectar guides, according to some researchers, increase foraging efficiency and ultimately, the likelihood of pollen transfer. Pollen gets disturbed inadvertently in the nectar gathering process and plants get pollinated; and that’s the plant’s reward: continuation of the species.


The artistry of the noticeable-to-human-eye nectar guides includes a variety of patterns, straight thin lines, contrasting center color, shades, hues and tones, radiating and non-radiating speckled guides, peripheral dots and contrasting petal color.


I’ve been collecting photos of plants with obvious examples of nectar guides. I don’t have a favorite, they’re all so beautiful. I’ll start with Esperanza, Tecoma stans. I was delighted to find the arrival of a fresh bouquet of yellow bells at the back of my butterfly garden during this chilly, wettish week. They have dynamic nectar guides: the dark gold lines running down the throat of the corolla.


Esperanza, also called yellow bells, Tecoma stans. (Photo by Anita Westervelt)

Runyon’s Violet Wild Petunia, Ruellia nudiflora var. runyonii, have similar guides in deep purple.

Runyon’s Violet Wild Petunia, Ruellia nudiflora var. runyonii. (Photo by Anita Westervelt)

They appear to work, having attracted this Western giant swallowtail butterfly.


Western giant swallowtail butterfly with Runyon's violet wild petunia. (Photo by Anita Westervelt)

A British study with bees** and speckled flowers with a radiating arrangement, found that dotted lines were more attractive than continuous lines; a group of dots was more attractive than a black circle in the centre. A disruptive outline increased attractiveness.


Cenizo, also called Texas purple sage, Leucophyllum frutescens, a local native that will be blooming soon, has awesome speckled nectar guides.


Cenizo, also called Texas purple sage, Leucophyllum frutescens. (Photo by Anita Westervelt)

Don’t rule out Mexican Caesalpinia, Caesalpinia Mexicana. Look beyond the large carpenter bee in the photograph to the orange brush strokes on the flower petal at the bottom right of the photo and just above the bee's head.


A large carpenter bee on Mexican Caesalpinia, Caesalpinia Mexicana. (Photo by Anita Westervelt)

Sunflowers, like our native Common sunflower, Helianthus annuus, are one of many flowers that have nectar guides visible only when viewed in ultraviolet light, which would reveal a darker center where the nectaries are located. They often have specific patterns on the petals as well when viewed under ultraviolet.


Common sunflower, Helianthus annuus with invisible (to humans) nectar guides. (Photo by Anita Westervelt)

The contrasting petal colors of Indian blanket, Gaillardia pulchella, below, guide flower visitors to nectar in the center of the bloom.


Indian blanket, Gaillardia pulchella. Photo by Anita Westervelt)

Other stunning examples of nectar guides are seen in the following photographs.


Pink evening primrose, Oenothera speciosa. (Photo by Anita Westervelt)

Ivy morning glory, Ipomoea hederacea. (Photo by Anita Westervelt)

Snapdragon vine, Maurandya antirrhiniflora. (Photo by Anita Westervelt)

Jann Miller’s Mauve Indian Mallow, Abutilon hulseanum. (Photo by Anita Westervelt)

Purple Groundcherry, also called Chinese Lantern, Quincula lobata. (Photo by Anita Westervelt)

Flowers have other traits that assist insects in getting nourishment. Some flowers have landing pads to allow the critter visitor to land and feed. A plant can use fragrance to attract particular pollinators from a distance, like plants that increase their scent at night to attract pollinating moths. Sacred Datura, Datura wrightii, and night jasmine, Cestrum nocturnum, are two plants that are deeply scented at night but seem to have no scent at all when the sun is up.


All these botanical marketing strategies help in species propagation. Of course, we all want that.


An interesting article about butterflies and nectar guides mentioned how extensive and highly complex the interrelationships between plants and butterflies really are. “Butterfly vision differs greatly from our own,” wrote Jane Hurwitz in a gardening article on the Internet. https://ahsgardening.org/wp-content/uploads/2020/03/Butterfly-Gardening-TAG-JF19.pdf

“When looking for flowers, flying butterflies recognize blocks of color, so massing one particular species of plant in a group increases the likelihood that passing butterflies will be attracted to your welcoming garden.”


This further enforces the concept of planting single-stemmed plants in groups of five or seven, that Wizzie Brown, a senior extension program specialist and board-certified entomologist with a specialty in Urban Entomology with the Texas A&M AgriLife Extension Service in Austin recommends. Odd numbers create appeal and help the eye move around, according to plantaddicts.com – in case you’re wondering. Professor Brown’s comment as to odd numbers in a group was similar.


Butterflies, like bees, see in the ultraviolet portion of the light spectrum – that’s where we cannot see – which allows butterflies to view flowers in a way that we cannot. “Once butterflies get close to flowers,” said Hurwitz, “certain details in the light reflected in the ultraviolet range provide them with important clues about the availability of nectar. The ultraviolet nectar guides on a flower’s petals direct butterflies toward the center of the flower where they can quickly access the flower’s nectar.”


Since length of a butterfly’s life span varies from species to species, Hurwitz points out that during their short lives, butterflies must mate and, if female, find an appropriate egg laying location. “During all this activity, they must also find and drink enough nectar to sustain their energy levels.” Nectar guides on closing flowers are not visible, which helps butterflies not waste time on a waning or depleted nectar source.


Here’s how we can help flower visitors: plant more flowers –a task after my own heart’s desires.


And that said – here's how easy it is to get more plants: Visit the 32nd Annual Rio Grande Valley Home and Garden Show at the McAllen Convention Center, March 31 through April 2.


South Texas Border Chapter Texas Master Naturalist members will have an outreach booth and native plant sale during the three days and be available to answer questions and discuss beneficial use of native plants in home landscaping. We’ll have many of the native nectar and pollinator plants I’ve mentioned in this blog and many others.


In addition, several of us will be speaking at the gardening stage during the three day event, providing PowerPoint presentations on the following subjects: nectar plants for all year blooms for a small garden plot; how native plants provide food and shelter for night-flying insects that in turn feed bats; how some of our most common annoying plants benefit native wildlife; friendly outdoor lighting options to minimize negative environment effects; and the care and feeding of a most unusual and beautiful native plant, the passion vine. A schedule of times will be available at the outreach booth. Look for the green shirts.


Alternately, if you can't wait until the Home Show, here's a list of Valley Native Plant Growers. Be sure to call to get directions and times before heading out:


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*“Plant Identification Terminology; An Illustrated Glossary” by James G. Harris and Melinda Woolf Harris, second edition, Spring Lake Press

**by J.B. Free journal article “Effect of Flower Shapes and Nectar Guides on the Behaviour of Foraging Honeybees.”

Also helpful in writing this article: A study by Lunau, K., Ren, ZX., Fan, XQ. et al. Nectar mimicry: a new phenomenon. Sci Rep 10, 7039 (2020) and www.nature.com

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