Defending the image of the learned botanist cum photographer that no one holds us to except ourselves, we spent weeks cultivating cuttings of a bizarre plant group we acquired from the field in troughs of mud and distilled water, dusting off the muck clinging resolutely to the plants with a fine brush, and suspending them in water on a lightbox to visualise and photograph.
Most people might assume that carnivorous plants thrive only in the remotest of tropical rainforests, when in truth, one would be hard pressed to find a body of freshwater in New England where carnivorous bladderworts prove elusive.
Distasteful as this may sound, bladderworts literally suck their prey into their traps. Their small traps are deflated pockets which when triggered by prey touching the hairs by the entrance, will inflate in a fraction of a blink of an eye, creating a negative pressure that sucks the prey into the trap filled with digestive enzymes. Mosquito larvae, nematodes, rotifers, water fleas and other microfauna typically fall prey to these highly derived traps.
We have witnessed a snail attached to a bladder of U. intermedia. Not entirely sure if it was a kleptoparasitic passer-by attempting to pilfer some prey, or perhaps it had fallen prey to the strong suction of the bladder. Either way, the snail freed itself eventually.
Connecticut plays host to 9 species of native bladderworts, alongside a pitcher plant, and three species of sundews (one of which has been extirpated from the state). Being the botanical geeks we are, we spent the season sleuthing about for these unassuming diminutive carnivorous plants that favour muck as a place to live. It was enthralling to think that given their underwhelming stature, there have been few modern monographic studies on them with exceptional photographic evidence, such that our images may help visualise microscopic morphological features previously unpublished.
Utricularia intermedia has become rare in most parts of Europe and in neighbouring Rhode Island due to population declines over the past 120 years. This species is not a floating species, but produces dimorphic root and stem structures. It produces green photosynthetic stems above soil level, while their white carnivorous traps grow below ground along a rhizome. Growing up to 5mm, their bladders make for splendid subjects for macro photography under a lightbox once meticulously purged of soil.
The most astonishing bladderwort we have met is Utricularia radiata, which we have encountered in only one site. This species produces air-filled floating rafts from modified leaves to hold their flowers aloft. Systematists find difficulty in resolving whether U. radiata should be kept separate from Utricularia inflata which was once thought to be restricted to the US southeast but populations of dubious taxon and origin have been reported from northeastern states since the 1980s.
Most native species of bladderworts in Connecticut bear yellow blooms. Utricularia purpurea is the exception that proves the rule, bearing pale lilac blooms with a charming orange center. Rootless and free-floating, their branching habit is rather distinct, and amply dramatic for the camera.
Naturalists in the 19th century used to name species in the New World after familiar species in Europe, and that legacy reverberates today in Utricularia macrorhiza. Too often it is mistaken for a similar European species, Utricularia vulgaris, which Latin epithet literally translates to “common”. Such elaborate filiform “leaves” they sport, that they make lovely subjects we spent hours on end fawning and fussing over.
Unlike the others, there is a singular species that grows above the water table in soggy peat bogs. Utricularia cornuta thrives in terrestrial habitats, producing inconspicuous grasslike leaves and the smallest of underground bladders. Their horn-like nectar spur makes them distinct from other yellow blooms and gives them their epithet name, meaning “horn”.
The most common species in Connecticut is Utricularia gibba, which has a cosmopolitan distribution. This plant defies all assumptions one would have of a plant, sans roots, sans leaves, looking little more than floating filaments of green. Their catholic choice of habitat made their presence ubiquitous in all waterways and lakes we have paid calls to, even the most disturbed. Their bladders are diminutive and too often entangled in green algae, but they offer up fields of yellow blooms inches above the water late in the summer.
It may be difficult to imagine how such frail-looking plants survive the long harsh winters of the American northeast. Several species grow as annuals; others produce specialised winter buds called turions, when growth turns to dormancy under diminishing temperatures and light. Turions are extremely condensed and thickened growth points that are cold hardy. In many species, they are so dense that they sink the generative tip to the bottom of the water column where it is unlikely to ice over.
They have no flamboyant pitchers, no menacing snares, no grandiose flowers, no foliage, but the lack of these characters make them no less fascinating in their coronet as the fastest moving plants in the world. Recent studies clocked their trapping speed at 4m s-1 with a startling acceleration that will put any car to shame of 28,000 m s-2 .
References
Adamec, Lubomír. 2020. "Biological flora of Central Europe: Utricularia intermedia Hayne, U. ochroleuca R.W. Hartm., U. stygia Thor and U. bremii Heer ex Kolliker". Perspectives in Plant Ecology, Evolution and Systematics, Volume 44, June 2020, 125520. https://doi.org/10.1016/j.ppees.2020.125520
Adamec, Lubomír, Andrea Kučerová. 2013. “Overwintering temperatures affect freezing temperatures of turions of aquatic plants”. Flora - Morphology, Distribution, Functional Ecology of Plants. Volume 208, Issues 8–9, 2013. Pages 497-501, ISSN 0367-2530, https://doi.org/10.1016/j.flora.2013.07.009
Poppinga, Simon, Lars Erik Daber, Anna Sofia Westermeier et al. Biomechanical analysis of prey capture in the carnivorous Southern bladderwort (Utricularia australis). Scientific Reports 7, 1776 (2017). https://doi.org/10.1038/s41598-017-01954-3
Urban, Rebecca A., John E. Titus and Wei-Xing Zhu. 2006. “An Invasive Macrophyte Alters Sediment Chemistry Due to Suppression of a Native Isoetid”. Oecologia, vol. 148, No. 3 (Jun., 2006), pp. 455-463.