Bladderworts and Other Bugivores

Drosera capillaris   Droseraceae

Horned Bladderwort (by JB)

Today John and George  explored  a small pond and adjacent Bald Cypress swamp margin in Jonathan Dickinson State Park near Hobe Sound in preparation for an upcoming educational event.   Carnivorous plants ruled today, so here we go on Bladderworts n’ stuff.   We scored a  Utricularia hat trick, encountered three different species all in flower in a small area.  Generally called Bladderworts,  the  genus contains 214 species altogether.

Zig-Zag Bladderwort (by JB)

Flesh-eating plants represent diverse plant families of Monocots and Dicots, and are not closely related to each other.   They have evolved in situations where the main plant nutrient, nitrogen in its various forms, is in short supply,  or where impaired root functions make it hard to take up, or where roots are absent altogether,  as in Utricularia. Insectivory  captures nitrogen in sterile sandy soils, in acid substrates, on epiphytic perches, in anoxic muds, and sometimes in aquatic habitats.  Utricularias look more like Algae than Flowering Plants—until you spot the beautiful flowers.

Genlisea with trap (Google Images)

The Genlisea traps are tubes, topped with two weird  long twisted appendages at the open end.   They look a little like those blow-up arm-flapping tube men they use to draw attention to used car lots and furniture sales.  The armlike appendages have inward pointing hairs.   Varmints swim in but can’t back out, because the hairs are a unidirectional valve,  as some fish traps catch fish.  The Genlisea traps are technically rolled leaves, so it is possible they evolved from simpler ancestors having in-curled blades resembling those of Pinguicula, making Genlisea sort of a “missing link” between simple Pinguicula and the complex traps in  Utricularia.   Perhaps relevant to this, Genlisea species have foliage leaves in rosettes  resembling those of Pinguicula.

Bladderwort bladder with trigger hairs (Photo by Jose Almodovar)

Utricularia traps are bladder-shaped or look like one of those goatskin wine squirt bottles favored by skiers.    The door leading into the bladder has a trap door.  Near the trap door are microscopic trigger hairs.  When the victim jostles the triggers,  the trap door releases and the bladder expands rapidly, sucking in the meal, as a slurp gun sucks in an aquarium fish. The in-slurp happens in a tiny fraction of a second.

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Today’s three Utricularia species are a study of variation within a single genus.   Leafy  Bladderwort  (U. foliosa) lives suspended gracefully in the standing water,  looking at first glance like a green alga waving in the pond.   It builds up huge slippery biomass.   Oddly, the species is distributed in the Americas and in Africa.

Leafy Bladderwort in water (by JB)

The other two, Zig-Zag  Bladderwort (U. subulata) and Horned Bladderwort (U. cornuta), inhabit  moist muds.   They both have fine threadlike leaves hidden in the soil.    They differ in their flower structures:  living up to its name (cornuta = horned), Horned Bladderwort has a long horn-shaped spur on the flower.   Zig-Zag Bladderwort is one of several species in ur area capable of making cleistogamus flowers: tiny flowers that self-pollinate (or somehow develop seed) and never open.

This species has a second quirk.  Where are the photosynthetic leaves?  It has some leaves but not much.  Botanist Wilhelm Barthlott and collaborators, citing earlier research, discuss this species as one of the few “carnivorous” plants that derives energy and not merely minerals from carnivory.

Around our feet, the Bladderworts had competition for the buggy menu.  The wet ground was littered with beautiful tiny Sundews (Drosera capillaris).  The reddish leaves on these are shaped like spoons and are covered topside with long hairs, each hair with a glistening glandular tip.   Insects who touch the tarbaby get in worse and worse as they struggle, until the goo-tipped hairs bend inward and press the corpses to the digestive leaf surface.

Sundew enjoying lunch (Photo by JB)