Micrasterias americana
Ehrenberg ex Ralfs, 1848
Most likely ID: n.a.
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Synonym: n.a.
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Sampling location: Vogelsberger Weiher (Austria)
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Phylogenetic tree: Micrasterias americana
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Diagnosis:Â
- cell longer than wide, outline broadly elliptical
- length 100–160 µm, width 81–145 µm
- semi-cells 5-lobed
- sinus deep, closed linearly inside, opening outward
- notches between first-order lobes shallow
- second-order lobes distinctly toothed
- apical lobes are trapezoidal, set off from the lateral lobes
- either side of the isthmus a distinct wart
- pair of warts at base of notches to apical lobes
- cell wall punctate
- chloroplasts with scattered pyrenoids
In June 2026, a mass development of Micrasterias americana was found by Michael Butkay in the Vogelsberger Weiher in Austria. He kindly made a subset of the sample available to me. In the samplings sites in my area I have not yet been able to find Micrasterias americana.
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Micrasterias americana can easily be recognized by the clearly separated apical lobes, which are distinctly set apart from the lateral lobes by a neck-shaped extension. The ends of the lobes bear only short spines, and the indentations between the secondary lobes are approximately U-shaped. In addition, at the base of the indentations leading to the apical lobes there is in each case a pair of warts, which can be clearly seen when the focal planes is adjusted on the cell surface (s. fig. 1 b).
Fig. 1 a-b: Micrasterias americana. L = 150 µm. Two focal planes of a specimen in DIC. Note the pair of warts at the base of the notches of the apical lobes (arrows). Obj. 60 X.
Fig. 2 a-b: Micrasterias americana. L = 150 µm. The same specimen as shown in fig. 1 a-b in brightfield illumination. Obj. 60 X.