Duckweeds Minnesota (2)
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Duckweeds From Minnesota (2)
 Duckweed Genera In Jepson Manual by W.P. Armstrong      Duckweeds In Flora Of North America by E. Landolt 
© W.P. Armstrong 5 August 2011
Duckweeds From Clearwater County, Minnesota (25-26 July 2011)

Lemna turionifera from First Lake, Second Lake, Spike Lake & Johnson Lake

Lemna turionifera showing the underside (ventral surface) suffused with red anthocyanin. Lemna minor typically does not have the conspicuous blotches of reddish anthocyanin. In addition, the upper (dorsal) surface has a midline row of minute papules typical of L. turionifera. L. minor typically does not have this row of papules on the dorsal surface. No turions were observed in these samples.

Second Lake: Lemna turionifera, Spirodela polyrrhiza, Wolffia borealis & W. columbiana.
Photo images taken with Nikon D-90 with AF-S VR Micro-Nikkor 105 mm macro lens and Kenko Automatic 3 Ring Extension Tube Set DG. Camera and accessories mounted on a Bogen 3205 Professional Tripod.

Second Lake: 1. Spirodela polyrrhiza, 2. Lemna turionifera, 3. Wolffia borealis, 4. Wolffia columbiana. The general shape and length of mature plant bodies fit W. columbiana rather than W. globosa (See next image from San Diego County, CA). The W. mature plant bodies of W. borealis & W. columbiana were 1.0 mm long. W. globosa is generally 0.5 to 0.9 mm with a more cylindrical body. In fact, it was once named W. cylindracea. In the U.S. W. globosa is known from California and Florida.
Dense population of Wolffia species from the San Dieguito River (Below Lake Hodges Dam) in San Diego County, California:


A. Wolffia columbiana (appearing darker green).

B. Wolffia globosa (smallest plants in photo).

C. Wolffia borealis (flat-topped with pointed apex).

Image scanned from 35mm color transparency. Original photo taken with Nikon FM-2 through Bausch & Lomb dissecting microscope with Kodachrome 64 film.

Second Lake: 1. Wolffia borealis, 2. Wolffia columbiana, 3. Lemna turionifera, 4. Spirodela polyrrhiza. Wolffia borealis has a dark green, punctate dorsal surface that floats above the water surface. This species was once named W. punctata. The transparent green dorsal surface of W. columbiana floats submersed just below the water surface, with only a small central portion exposed above the water line.

Second Lake with backlighting only: 1. Spirodela polyrrhiza, 2. Lemna turionifera, 3. Wolffia borealis, 4. Wolffia columbiana. Wolffia borealis shows up dark green while W. columbiana is transparent green. The 3 veins of L. turionifera are visible. The other North American 3-veined duckweeds, including L. minor, L. gibba, L. obscura, L. perpusilla, L. aequinoctialis, and L. trisulca, can be ruled out.

Close-up view of duckweed sample from Second Lake. Wolffia borealis (1) and W. columbiana (2). The average length of each Wolffia plant body is 1.0 mm (1/25th of an inch). Image taken with Sony W-300 through Bausch & Lomb dissecting microscope. Magnification 15x.

Flowering (Protogynous) Wolffia columbiana From Second Lake

Flowering Wolffia columbiana from Second Lake. On individual plants, maturation of minute flowers within the dorsal floral cavity is protogynous: The stigma is receptive before the anther releases pollen. When the stima is receptive a droplet of stigmatic fluid is secreted. By the time the anther has split open and released pollen, the stgma has already dried and withered. This strategy favors cross pollination between different plants. Image taken with Sony W-300 through Bausch & Lomb dissecting microscope. Magnification 20x.

Flowering Wolffia columbiana from Second Lake. A mass of pollen grains have been released from a dehiscent anther within the floral cavity. Image taken with Sony W-300 through Bausch & Lomb dissecting microscope. Magnification 25x.

Protogynous Wolffia columbiana from Second Lake. The stigma has already dried and withered. The anther has not yet released the pollen grains inside. Image taken with Sony W-300 through Bausch & Lomb dissecting microscope. Magnification 40x.

Duckweeds From Clearwater County, Minnesota (28 July 2011)

Probably Lemna minor from Clearwater Lake.

A. Lemna minor (probably). The midline row of dorsal papules is not clearly discernible as in L. turionifera. Unlike L. turionifera, reddish anthocyanin is not present on either the dorsal or ventral side. B. This plant has a midline row of dorsal papules characteristic of L. turionifera. The majority of plants in this collection (#11024) seem to fit L. minor rather than L. turionifera; however, without evidence of turions produced in the fall I cannot be 100% certain.

A. Lemna turionifera from Moose Lake. The plant body has a distinct midline row of dorsal papules and is suffused with reddish anthocyanin. B. Lemna minor (probably) from Clearwater Lake. It does not have midline row of dorsal papules and does not have reddish anthocyanin.

A. Lemna turionifera from Moose Lake. The plant body has a distinct midline row of dorsal papules and is suffused with reddish anthocyanin. B. Lemna minor (probably) from Clearwater Lake. It does not have midline row of dorsal papules and does not have reddish anthocyanin. Some plants have a minute apical papule,

Transparent view of Lemna minor from Clearwater Lake. Another characteristic used to separate Lemna minor from L. turionifera is the position of greatest distance between the lateral veins (inner lateral veins): In L. minor the widest point is near the middle of the veins or below (proximal). In L. turionifera it is near the middle or above (distal). Since the widest distance can be near the middle in both species, this trait is not always that useful.

Duckweed Dilemma: Lemna turionifera or L. minor

West Four-Legged Lake, Clearwater County, Minnesota

Some of these Lemna have a row of minute papules on the upper (dorsal) side. Without any reddish anthocyanin on the underside or turions, I must conclude that they are L. turionifera; however, some plants simply do not have a discernible row of papules. Are these plants L. minor, or are they L. turionifera with poorly developed papules? All I can say regarding the species composition of this collection is L. turionifera, possibly intermixed with some L. minor. I just can't be 100% certain about the presence L. minor. Ideally, the lake needs to be resampled in the fall to look for the presence of turions.

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