Story behind the art of Donnett Vanek

28th Annual International

American Society of Botanical Artists and Marin Art & Garden Center

Thigmonastic Stamen of Opuntia basilaris var. treleasei and pollinator

Opuntia basilaris var. treleasei, Agapostemon texanus

Less than an hour from where I live in California is Wind Wolves Preserve, one of my favorite places to spend the day. The Preserve is an ecologically unique region where the Transverse Ranges, Coast Ranges, Sierra Nevada, western Mojave Desert, and San Joaquin Valley influences converge. Wind Wolves Preserve has an elevation range from 640 to 6,000 feet. Due to this range in elevation, the Preserve transitions from rolling grasslands on the San Joaquin Valley floor into California blue oak, valley oak, and cottonwood savanna. The savanna ascends into juniper and pinyon forests transitioning into towering stands of ponderosa pine and bigcone spruce.

The Wildflower Loop at the entrance of Wind Wolves Preserve meanders through the rolling grassland. When there is the perfect amount of sunshine and precipitation, the grassland explodes with colorful wildflowers. At the beginning of the Wildflower Loop, there are clusters of small cacti in the beavertail family. If they are not in bloom, it is easy to walk by them. At first glance, they look like any Opuntia growing in many regions. They are not just any Opuntia though. These are the rare and endangered Opuntia basilaris var. treleasi, Bakersfield cactus. The differences between the Bakersfield cactus and other beavertail cacti are subtle. The pads of the Bakersfield cactus are smoother than other beavertail cactus and are dotted with areoles that contain barbed bristles and spines. Most beavertail cacti produce juicy edible fruit; the fruit of the Bakersfield cactus is dry with grayish-white seeds in it. The Bakersfield cactus grows in a small geographic range and is endemic to Kern County, in the southern San Joaquin Valley, California. At one time there were many populations of this small cactus. However, because of urban sprawl, oil and agricultural development, little native habitat is left, and there are few populations of the cactus. In 1990 it was federally and state listed as endangered. The cactus is listed as CA Rare Plant Rank 1B.1, Plants Rare, Threatened or Endangered in California and Elsewhere; Seriously threatened in California (https://rareplants.cnps.org:443/Plants/Details?taxon=Opuntia+basilaris+var.+treleasei). Wind Wolves Preserve is at the forefront of a successful preservation and propagation program of the Bakersfield cactus. Each cluster of cacti has a rebar stake with an ID number on it.

I have been enthralled with this cactus ever since I came across it many years ago at Wind Wolves Preserve. After reading and researching about its status, I decided to document it through my artwork. Thigmonastic stamens of Opuntia basilaris var. treleasei and Agapostemon texanus, pollinator, is the fourth piece in a series of artworks. 

The first time I saw the Bakersfield cactus, it was in full bloom with glorious magenta flowers. The bright flowers stood out in stark contrast to the greens and browns of the surrounding grassland. It is easy to just look at the spectacularly beautiful blossoms and continue on your way. However, if you stop and look closely into the flowers, there is a whole new world of wonder. When I looked, a menagerie of industrious insects wove in and out of the graceful stamens that encircled the pistil of the flower. Diadasia australis californica, cactus bees, were busy wending their way through the stamens deep into the flower, seeking out pollen. And my favorite bee, Agapostemon texanus, sweat bee, landed on the stamens, its bright green color in sharp contrast to the magenta flower. When the bees and other small insects moved around the flower, they touched the filaments. I observed that the stimulation caused movement of the stamens towards the center of the flower. Soon the lower layers of the anthers and filaments were densely packed around the style of the pistil, hidden under the upper anthers and filaments.

I was curious about this. I read that the movement I observed is a thigmonastic or nastic (non-directional) response to stimuli, meaning that the movement of the stamens is not towards the stimulus, but instead towards the style of the flower. This movement can protect the anthers with the most pollen, placing them in tighter, compact lower layers around the style, like what I had observed out in the field. Bees that pollinate the cactus dig deep into the flower seeking out the anthers with the most pollen. As they crawl back up through the filaments and anthers, pollen is deposited on them and they go on to pollinate other flowers of the Bakersfield cactus. Cactus bees and sweat bees are potential pollinators of the Bakersfield cactus. I decided an interesting addition to my series of work on this cactus would be to render a close-up of the stamens with one of the bees that visit it. I used the traditional technique of silverpoint on paper with silverpoint ground. I rendered the bee in drybrush watercolor and the accents on the anthers of the stamens and wings of the bee in shell gold. I chose the sweat bee for the composition because of the stark contrast between the bees bright metallic green color and the subtle tones of silverpoint.

Not all opuntia have thigmonastic stamens. I am not a botanist or scientist. My title “Thigmonastic stamens” refers to my observations, and what I think may be the type of stamens of the Opuntia basilaris var. treleasei.

Most of my work is focused on California native plants that I have observed on walks in nature preserves. As a botanical artist, I feel I can educate viewers through my artwork and encourage them to consider the beauty and importance of the natural world around us.

For more information about thigmonasty, see:

*   https://www.biologyonline.com/dictionary/thigmonasty

*Thigmonastic stamens of prickly pear /opuntia -

https://awkwardbotany.com/2015/06/10/year-of-pollination-stamen-movement-in-the-flowers-of-prickly-pears/

* https://www.nature.com/articles/s41598-018-32384-4#ref-CR41

*Potential pollinator of Bakersfield Cactus - https://www.fws.gov/species/bakersfield-cactus-opuntia-treleasei  Scroll down to “life cycle”

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Read more about this artist's work: 27th Annual