Tag Archives: fluorescence

More Science Experimentation At Grad Student Prices: Fluorescence in Carnivorous Plants

One of the few bits of unadulterated good at the gallery over the last three months involved going through the back storeroom and sorting through boxes that were packed frantically back during the Great Move of 2017 and hadn’t been resolved before now. Among many other things, one of those boxes contained a set of ultraviolet rock lights purchased in better times to examine fluorescence in both minerals and in carnivorous plants. No better time than the present, and it was also a great excuse to hunt for scorpions.

Regular readers may remember some previous experiments in inducing fluorescence in pitcher plants a few years back, but these had problems for multiple reasons. The first is that not all UV lights are equal: to get the right light frequency, about 380 manometers, shortwave UV lights are much more desirable than longwave UV lights. Most standard UV LED lights, such as those for checking UV ink handstamps in nightclubs and bodily fluid stains in nightclubs and other venues, are longwave lights, so while they’ll make tonic water and urine fluoresce, they don’t do a lot for getting a positive response out of most carnivorous plants. Shortwave UV lights, generally used for fluorescent mineral identification, produce the correct wavelength, but they’re both expensive and very hard to use. Most shortwave UV lights require alternating current and extension cords, meaning that they have all sorts of hazards when used in typical carnivorous plant habitats. Worse, those lights have to get in CLOSE to see plant fluorescence, and while some flowers will fluoresce at a distance under shortwave UV (aloes in particular), carnivore traps need to get that light within about three to five centimeters to fluoresce. Obviously, for basic identification and study of the phenomenon, especially in the field, another option was necessary.

Back in 2013, I tried an alternative with a violet laser pointer and a beam diffuser, essentially creating a UV laser flashlight. This had its own issues. The beam diffuser had to be adjusted constantly for best effect, which didn’t leave hands free to adjust plants, use a camera, or much of anything else. In the same vein, standard digital cameras at the time were beyond horrible for photographing UV fluorescence, so a lot of plans had to be set aside. The plan, though, was to run a demonstration of carnivore fluorescence at the old gallery in the summer of 2017, and we all know what happened there. The gear went into a box, the box went on a shelf in the new gallery storeroom, and it took a pandemic inventory and reorganization to pull the gear out again.

Believe it or not, the revelation wasn’t due to the existing shortwave UV gear, and it wasn’t due to carnivorous plants. The main plan was to prospect for Texas opal along the Brazos River. Most Texas opal deposits aren’t what would be considered gem-grade, especially compared to Australian boulder opal, but it was once harvested in great quantities in the 1930s and shipped to Europe, where it had quite a popularity when sold as “black opal” in the days before World War II. Today, it can be found through Pennsylvanian marine fossil deposits, commonly turning up inside crinoids and horn corals, and like most other opals, it fluoresces a gentle peach color under shortwave UV. It’s one thing to see it in a static museum display and another to see it in situation, so the box came out to a ranch between Mineral Wells and Palo Pinto in West Texas in order to examine those opal deposits firsthand.

Well, inside the box was also a planned experiment delayed by the move to the new gallery. American Science & Surplus sells a lot of interesting items, with its only limitation being an inability to ship items outside of the United States. (I’ve spent the last 15 years searching for an international equivalent for friends seeking scientific surplus, and have yet to find anything comparable.) Among many other wonders, AS&S carries a wide line of 5-milliwatt laser pointers, including the violet laser pointer I was using. More importantly for those discussion, AS&S carries a set of kaleidoscope pointers. The red and green ones get quite a bit of use at music festivals and the like: twist a frontpiece and push the button, and you have your very own laser disco ball. Twist the frontpiece a bit more to spread the beam from many distinct spots to even more diffuse individual spots, and you have laser light going everywhere. Again, important for this discussion, AS&S sells violet kaleidoscopic laser pointers selling for $16US, and one of them was in the box of UV gear, untouched since 2017.

At first, it was just a lark. Turn it on outside and ask “Hmmm…is anything glowing?” That’s when a few pieces of scrap paper started fluorescing, but was that fluorescence or just good night vision? I had a way to test it, thanks to a few chunks of slag uranium glass brought along for the trip, so it was a matter of pulling them out, turning on the laser pointer, and then photographing the effect both with flash and without:

Next experiment: using others’ research. I had recently read about archaeologists using shortwave UV to spot damage to bones that was impossible to view under visible light, including damage caused while the organism was still alive or shortly after it died, and a feral pig jawbone discovered on the ranch was a great test. While barely visible under sunlight, the laser pointer revealed damage to the sides of the jaw, possibly from coyotes feeding on the carcass after the pig died. (At least, I hoped these were from coyotes.)

The real test, though, came from random fossils collected through the area. The real surprise wasn’t discovering that opalized fossils fluoresced under UV. The real surprise was finding several brachiopod fossils that fluoresced in different colors, which may require a trip to the Mineral Wells Fossil Park to test this further.

With this knowledge, it was time to go back to Dallas and the gallery to test the laser pointer on carnivores. After several days of examination with various genera and species, the real limitation wasn’t with the laser pointer, but with using digital cameras to record it. Even with a new iPad camera, generally considered one of the most sophisticated cameras available on the market, most carnivore fluorescence is only visible when the UV source is within about two centimeters from the trap, and most of it is invisible to the camera. Obviously, more research is needed, but several things turned up, including a few that wouldn’t have been obvious.

Firstly, while UV fluorescence has been observed with a wide range of carnivorous plants, the laser pointer only spotted fluorescence with several genera. Venus flytraps and sundews were known to fluoresce along the leaf surface, but the only fluorescence spotted with the laser pointer was along leaf edges, suggesting that the previously observed fluorescence may range in bands visible under multiple wavelengths of UV in order to attract multiple varieties of insect. Butterworts were already known not to fluoresce, but spots in the blooms of Pinguicula primulflora and P. gigantea glow extremely strongly, as do the blooms of bladderworts. The carnivorous bromeliad Brocchinia was particularly interesting: its traps display multiple arrays of fluorescing bands, but dying leaves on the outside of each plant harbor fungus or mold that fluoresces to black-light poster levels, an effect that I had seen previously on ginger plants in Nicaragua, and may assist the spread of spores via beetles or other insects. Most interestingly, while the trapping surfaces of the frail triggerplant Stylidium debile do not fluoresce, shining the laser pointer directly down the blooms reveal a small but bright fluorescing spot, suggesting the main attracting point for pollinating insects.

It’s the four genera commonly referred to as “pitcher plants” that the widest range of fluorescence was observed. The Australian pitcher plant, Cephalotus follicularis, showed no fluorescence at all under the laser pointer, suggesting that any natural fluorescence might be at a different wavelength. South American pitcher plants (Heliamphora) show spots of fluorescence across species, usually centered around the nectar cup at the top of the pitcher, that unfortunately was impossible to capture with any digital camera I had on hand. North American pitcher plants (Sarracenia) showed subtle but definitive fluorescence along the lip of four observed species and two hybrids, with suggestions that the observed brightness of white pitcher plants (Sarracenia leucophylla) in moonlight is due to reflectivity of visible light and not fluorescence under reflected UV. The greatest levels of fluorescence, though, were spotted in multiple species of Asian pitcher plant (Nepenthes), usually manifesting as a brilliant dark green under the laser pointer. Even under a digital camera, the whole of the peristome stands out under UV except under certain situations. Those situations include newly opened pitchers (fluorescence doesn’t appear in pitchers for three to five days, coinciding with the amount of time the fluid inside of the pitchers needs to be exposed to air before its acidity reaches its peak), and with species already known not to be carnivorous, such as Nepenthes hemsleyana and Nepenthes ampullaria.

For the most part, Nepenthes pitchers fluoresce very strongly using this technique. Below are photos in visible light and in UV of the Nepenthes hybrid “Bill Bailey” and of Nepenthes veitchii:

Obviously, this is just the beginning, as these photos don’t take into account fluctuations based on season, photoperiod, or average temperature, or if the fluorescence increases or decreases based on the amount of prey captured at that time. That said, for the cost of a violet kaleidoscopic laser pointer, testing this will be considerably easier, and can be conducted by nearly anybody. Let’s see what we find out next.