DO BEARS DISPERSE DARLINGTONIA? Damon Collingsworth • California Carnivores • 2833 Old Gravenstein Hwy. • Sebastopol • California 95472 • [email protected] Sodden fields ofsilent green serpent heads complete with dark red tongues stretch out before me as I explore theNorthernCaliforniahabitat ofDarlingtonia californica-the CobraLily. Closer examination of their domed heads reveals the clear patches or fenestrations which trick insects into following the light down into the pitchers. As I marvel at these fascinating plants, I askmyself rhetorically, “How could they be any more interesting?” Well, what iftheir seeds were distributed by bears? This isn’t exactly a new idea, but it hasn’t been widely accepted as fact either. Peter D’Amato has long suspected this to be true. He even mentioned it in the first edition ofhis book, “The Sav- age Garden”. Peternotes, “the small seeds are bristly, no doubtto encourage dispersal by animals.” Indeed, the little club-shaped seeds are covered intinybristles that immediately make youthink ofanimaldispersal. Bearsareanobvious suspectbecauseoftheirlong, shaggyfurandloveofwater. In2003 HarryTryontookPeterandmeto aDarlingtonia sitethathe calls “bearwallows” inDel Norte County, California. His redpickup truckjostledus downnarrowtimber“roads” composedof loose rock, a crumbling uphill slope to the right, and a sheer drop ofat least 50 meters to the left. Peter leaned infromthe back seat andasked, “Ifwe fell how long do youthinkitwouldtake to find ourbodies?” Figure 1: Harry Tryon leads the way to “Bear Wallows”, with a Darlingtonia-lined wallow beyond him; and an American black bear (Ursus americanus). Left photo by Damon Collingsworth; right photo by U.S. Fish and Wildlife Service. 44 Carnivorous Plant Newsletter Shortly afterthe uneasy laughter died down, the truckthankfully came to a stop. As we got out, Harry pointed out bear tracks and warned us. He said that he never visits this spot by himself. We followedhim quietly down a trail to the wallows. I noticedbearhair stuck on the low branches and bark ofthe tree trunks as I walked. The trail led us downhill a ways and ended in front ofa bear- sized pool bordered by Cobra plants. Our path literally dumped into the wallow and then climbed outonthe othersidebefore dropping into anothercoolpool.AsIrecall, thepathledthroughatleast three more ofthese small pools, each surrounded by Darlingtonia. Thankfully the wallows were not in use at the time, but theirpurpose was clear. Bears must surelytake this path to cool down. It was an amazing site where, probably due to the relatively low light, theDarlingtonia growpitchers that are aboutwaisthigh. While this evidence is admittedly largely circumstantial it does lend some credence to the ideathatthe seedwere hitchhiking onthe bears to findareasto germinate wherethe water can cool the plants’ roots on hot summer days. Years later, after a Darlingtonia talk I gave at the 2012 ICPS conference, Dr. Adam Cross ap- proached me. He was quite intrigued by the bear idea in particular and offered to do a SEM image ofDarlingtonia seed. Hehas done quiteabitofresearchonseeddispersalinAustraliaandsohisin- sightshave beeninvaluable. WhenIreceivedthe initial SEMimages ofthe seed(Fig. 2), Iwas alit- tledisheartened.Thebristleslackedbarbs orhooksthatmightmore firmly suggestanimaldispersal. Inpersonal communicationwithAdam, he pointed out that the dispersal objective ofDarlingtonia is very unique, whichmight account forthe somewhattame look ofthe bristles. Ithas beenpointed out by others that the bristles would also add surface area to the seed allowing them to float better onthe surface ofwater. This might suggestthatthe bristles are purely forwaterdispersal, but given the vast expanses ofhot and dry landscapes that Darlingtonia seeds have traveled to find the cool streams andfens where they grow, it seems thatwaterdispersal certainlycannotbe thewhole story. AdamandIwouldpointoutherethatthe idealdispersalmodelforDarlingtoniawouldbeforthe seeds to be bristledjustenoughto hang inthe shaggyhairofawanderingbear, butnot so hookedas to get stuckpermanently in their fur. Bears are wallowers, so Darlingtonia seeds deposited in their fur would have a good chance of finding their way into some water. Once in the water, however, the seeds will need to release from the hair into the water and float to some suitable location for germination. We believe it is this two-step distribution that explains why the seed don’t look more aggressive when comparedto othermore typically animal-distributed seeds. Figure 2: A close look at the seed coat projections which enable the seeds to entangle in the hair of animals. Photo by Adam Cross. Volume 44 June 2015 45 Figure 3: The full progression of Darlingtonia flowers, starting with the freshly opened flower in the left background. In the foreground from bottom to top, each flower shows how the flowers turn up after pollination; and on the right, a nearly ripened seed pod fully upturned. I’ve spent quite a bit oftime walking amidst the Cobra plants now and I have noticed another trait that further sup- ports this theory of bear-dispersal. Like Sarmcenia, Darlingtonia flowers are born on tall scapes and they hang like little green andpurple lanterns. Once the flower is pollinated, the scape straight- ens out turning the fruit upside down before it dehisces. By autumn, the fruit cracks open slightly longitudinally, but because the fruit is upturned like a cup, nearly all of the seeds are stuck inside. This would be a pretty big evolutionary flaw for a plant family which is so spe- cialized and evolved. The common sense ofnature dictatesthattheremustbe some evolutionary advantage to this. Sarrace- niaflava andS. leucophylla flowers often Figure 4: A fully opened seed pod from above turn up after pollination, but this helps showing the seeds still trapped inside. Photo by the seeds to fall away from the umbeli- Jason Ksepka. 46 Carnivorous Plant Newsletter formpistil. InSarracenia, theupturnedpistil canalso shadethe developingfruitfromthe scorching southern sun afterthe flowerhas inverted. So, why do Darlingtonia flowers then seem to stupidly invert and trap their seeds in their own fruit? It would take less energy to leave the flower the way it is andjust drop the seed in the water below ifwater dispersal was your sole goal. After thinking about this long and hard, I propose that the seeds are not stuck, but waiting for a A ride. very few seeds often do immediately fall from the openings inthe side ofthe driedfruit and might very well disperse a short distance in the water below. Almost all ofthe other seeds are still stuck in the open fruit even a year after they’ve opened. You often see last year’s pods still full of old seed. I have noticed that as I troop through the Cobra plants, I brush past the tall, stiffscapes. They would be pushed down slightly, then spring back to attention, flinging the seeds everywhere. No doubt, as bears lumberthroughthe water-loggedplants the seedwouldbe flung into their fur in the same way. Obviously, seeds thathave fallenon the groundare much less likelyto casuallymake theirway into the furofan animal, making the type oflong distance dispersal necessary forfinding newhabitatunlikely atbest. Strangelythen, falling immediately out ofthe fruitbecomes evolution- arily limiting ifnot truly disadvantageous. Although, water is an obvious part ofDarlingtonia’s seed dispersal strategy, particularly within suitable habitat once colonized, animal dispersal is almost certainly key to colonizing new suitable habitat. Miles and miles ofdry rocky hills often separate Darlingtonia sites. How else would their seeds traverse all ofthis unsuitable landto findtheirvery specific and often isolatedhabitat? In comparison, the most likelymechanism forSarracenia colonization ofnew habitat is almost certainlywind, despitetheirseeds’ratherrotundappearance.The southeasternUnited States is infa- mous forbothhurricanes andtornadoes, butthey canoccuralongthe entire eastern seaboard ofthe U.S. The Atlantic hurricane season starts in July and ends in November. Sarracenia seeds usually A mature by lateAugust and pods are fully dehisced by late September to early October. Category 1 hurricane has wind speeds of 119-153 km/h and a Category 5 has winds >252 km/h. Tornadoes often occur within the hurricanes. A very weak tornado starts at 105 km/h and the biggest have winds exceeding 320 km/h. With severe weather like this, it is not hardto imagine how little round Sarracenia seeds, seed pods, or indeed entire plants might be scattered to every wet corner ofthe southeast. Especially whenyou combine that with what used to be a more contiguously wet region than California. Thankfully for us, the cold waters ofthe Pacific Ocean prevents strong hurricanes fromhittingNorthernCalifornia. Strongwinds canoccur, butthese majorwindevents are veryrare withthe worstwindusually at high elevation. Darlingtonia are more commonly found inwet areas betweenthe hills andmountains where they wouldbe mostlyprotected from strong winds. The few higherelevationpopulations would almost always be buriedby snowbefore orduringthese storms, as Californiaonlyhas strong storms inthe winter. This all makes significantwinddispersal ofDar- lingtonia seed improbable atbest. Due to the lack ofcredible fossil record ofthe family Sarraceniaceae, it is unclear where they initially evolved or even when Darlingtonia branched off. Regardless ofthe details, I think that a long-distance dispersal event via animals could be responsible for Darlingtonia’s far-flung range relative to Sarracenia. Indeed, it could have beenthat slight difference in the seed coat that carried the family to California where Darlingtonia diverged due to the extreme and long geographical isolation. Grantedthis is conjecture, but it is funto think about. Volume 44 June 2015 47