Utricularia intermedia

Flatleaf Bladderwort

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The natural history of the northwoods

Name:

• Utricularia, from the Latin, utricularius, "the master of a raft floated on bladders"
• intermedia, from the Latin inter, "between", and medius, "in the middle"
• Common name from the flattened leaf segments
• Other common names include: Intermediate Bladderwort, Mountain Bladderwort, Northern Bladderwort, Lus nam Balgan Meadhanach (Gaelic), Dybläddra, dyblåsört, mellanblåsört (Swe), Gytjeblærerod (Nor), Storlæbet Blærerod (Dan), Rimpivesiherne (Fin), Mittlerer Wasserschlauch (Ger), Bublinatka Prostredná (Slovak)

Taxonomy:

• Kingdom Plantae, the Plants
  • Division Magnoliophyta, the Angiosperms (flowering plants)
    • Class Magnoliopsida, the Dicotyledons
    • Subclass Asteridae
      • Order Scrophulariales, the
        • Family Lentibulariaceae, the Bladderworts
          • Genus Utricularia, the Bladderworts
• Taxonomic Serial Number: 34454

Description:

• A free-floating, annual aquatic herb of shallow waters.
• Leaves numerous, alternate, dissected, ¼"-¾" long, with individual segments flat and linear (hence the common name) and edged with tiny, bristly teeth.
• Bladders 2mm-4mm, born on separate branches from the leaves. These trap and digest small aquatic intertebrates.
• Stem very slender, creeping along the bottom in shallow waters.
• Bladders small, deflated, pear-shaped pouches. Not air-filled or used for floatation, they open abruptly when trigger hairs are disturbed, sucking in water and any hapless aquatic creature responsible for setting off the trap. Digestive enzymes and bacteria in the bladder then digest the prey for the nutritional use of the plant, a process typically taking 15 minutes to 2 hours, depending upon the size of the catch. When digestion is complete, special cells extract the nutrient-rich water from the bladder into the stem, thereby restoring the vaccuum and resetting the trap for its next victim.
• Roots absent
• Flowers yellow, perfect, irregular in form, rather resembling a snapdragon; usually 2-4 atop a stalk rising 2"-8" above the water's surface. Lower lip ¼"-½" long, nearly twice the length of the upper lip; lower spur nearly as long as the lower lip.
• Sepals 2-5
• Petals 5, united to form upper and lower lips
• Stamens 2
• Ovary superior (within blossom)
• Fruit a single chamber capsule, with central column bearing many seeds
• Turions (winter buds) ovoid or ellipsoid, 5mm-7mm long.

Identification:

• Identifiable as a Bladderwort by its aquatic habitat and distinctive bladders
• Distinguished from other North Country bladderworts by:
  • Bladders borne on specialized branches and not on the dissected leaves
  • Leaf segments with tiny, spiny teeth
  • Flower stalks which remain upright when in fruit

Distribution:

• Circumboreal; south in North America to Delaware, Indiana, Iowa, North Dakota, and California

Habitat:

• Bogs, ponds, swamps, lakeshores, and other shallow, standing, or slowly moving waters.

Associates:

• Aquatic: Coontail (Ceratophyllum demersum), Duckweeds (Lemna minor, Lemna trisulca, Spirodela polyrhiza)
• Mammals: Occasionally eaten by muskrats, but not a preferred food.
• Birds: Occasionally eaten by ducks and other waterfowl, but not a preferred food.
• Invertebrates (as prey): Fairy Shrimp (Branchiopoda), Water Fleas (Cladocera), Copepods (Copepoda), Scuds (Amphipoda). Also preys on paramecia, rotifers, nematodes, and microscopic insect larvae.

History:

• In 1875 it was Charles Darwin himself who, along with two other biologists, finally established that the bladders of the Bladderworts were not for flotation, as had long been assumed, but were instead sophisticated traps for tiny animals.

Uses:

• With the other Bladderworts, a distinctive, if difficult, native for the water garden

Reproduction:

• Sexually by seed
  • Flowers July-August
  • Insect pollinated
• Asexually by turions (winter buds), the most common method
  • Dense, starch-rich leaf masses form at tips of branches in late fall, dropping to the bottom and remaining dormant through the long winter.
  • Turions begin growing as spring water temperatures rise, absorbing air in their leaves to become buoyant.

Propagation:

• By seed.

Cultivation:

• Hardy to USDA Zone 3 (average minimum annual temperature -40ºF)
• Not generally available commercially.

Links:

• Den Virtuella Floren, Naturhistoriska riksmuseet, Stockholm

Comments:

• The bladderworts are the only predatory aquatic plants in the US.