Summer Botany: My “Crayola” Potato

Oh I do love purple …… not sure why? Anything purple and any shade of purple ….. even a hint of purple will do! As a kid (then and now) my most treasured possession was a new box of crayons. Breaking the seal and inhaling that delicious aroma of color (admit it …. you know the smell) was only the first step in my love affair. Removing each crayon, one-by-one, and taking them for a test drive soon followed, with special care and attention paid to the purples, with names like ……….

Vivid violet, wisteria, twilight lavender, pearly purple, purple pizzazz and purple mountain’s majesty. Who wouldn’t love cyber grape and lilac; or plump purple and sugar plum. How could here be so many purples!

So when I literally stumbled into a mound of the exquisitely purple-hued Silverleaf Nightshade, my surprise and delight was audible. While carefully removing countless nettle-like prickles from my hands, Roy heard me explain, “My “Crayola” Potato!”

Silverleaf Nightshade (Solanum elaeagnifolium), a (weedy) native perennial found throughout the Western US, is one of 90 genera with 3,000+ species belonging to the potato or nightshade family (Solanaceae). The genus Solanum has the largest number of species in the family and includes culinary favorites like tomato, potato, eggplant. The genus also includes black nightshade, buffalo bur, horsenettle, potato vine and kangaroo apple. You may be surprised to know that other members of the Potato family include bell, chili and habanero peppers (Capsicum genus), tomatillos, goji berries, and ground cherries (Physalis), petunia (Petunia x hybrid), tobacco (Nicotiana), jimsonweed (Datura) and belladonna (Atropa).

Alert!!!  Now if some of these plant names sound familiar in a troublesome way, it may be because they all contain toxic alkaloids. Even tomatoes, potatoes and eggplant! So handle with care. Luckily the toxin solanine (in the Solanum genus) is rendered safe for consumption when the fruit is mature (as in the tomato) or after cooking (as in the potato and eggplant). And many species in the Potato family, including Silverleaf Nightshade, have been used safely as medicinals by indigenous peoples, such as the Apache.  Uses of this species include:  The Isleta have eaten the raw seed pods or boiled them into a syrup for a laxative; as a snake bite remedy, the Zuni used fresh or dried root chewed by a medicine man before sucking the snake bite and applying a poultice to the wound; as a toothache remedy, the Zuni placed chewed root in the cavity of the aching tooth.

Did you know the genus Solanum includes plants with flowers that are self-pollinating? This means the assistance from bees and other insects, or wind is unnecessary for fertilization and fruit set. So why do insects prowl about Silverleaf nightshade or the tomato plants in your garden? What’s the point?  

While my “Crayola” Potato or your garden tomato will set fruit unaided by pollinators, scientists have made several cool discoveries:  1. Fruit set is more successful when the wind or your hand moves the flowers about to shake out pollen, and 2. Bees gotta have pollen! And they can retrieve pollen from self-fertile flowers by “Buzz Pollinating.” 

Buzz Pollinating! What the heck? Time for an extensive trip down the rabbit trail; there must be a rainy day in my future?  Meanwhile, in a nutshell, buzz pollination is a term used to describe how buzzing insects (bees) use vibrational energy to free concealed pollen grains from poricidal anthers (tube shaped anthers that hide pollen grains). Silverleaf nightshade was the study species in at least one published research project I found^1.    Curious scientists looked into the species of bees buzzing nightshade flowers, and studied the buzzing amplitude, frequency and duration to determine when and how successful each insect was in collecting pollen that dropped from the small pore in each anther. They even experimented with anther buzzing using an electric toothbrush!

Ok! Now this is creative excellent awesomeness! 

So the tubular anthers of these flowers face down allowing gravity to help the pollen grains “roll” out of the tubes where they make contact with the stigma and self-fertilize the flower.  But the flowers also provide a brilliant yellow, upside-down place for a pollen hungry bee to hang while she buzzes for food delivery! A bit too much buzzing and she’s also pollinating the flower.

Not only is the flower of the Silverleaf Nightshade a poppin’ purple with sunburst yellow anthers, but it’s biology has totally blown my mind! 

Nature rocks!

¹https://www.mdpi.com/2223-7747/10/12/2592/htm