Netrium digitus
(Brébisson ex Ralfs) Itzigsohn & Rothe, 1856
Most likely ID: n.a.
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Synonym: n.a.
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Sampling locations: Simmelried, Schwemm Moor (Austria), Lauchsee Moor (Austria), Paradieswiesen (Austria), Gieringer Weiher (Austria)Â
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Phylogenetic tree: Netrium digitus
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Diagnosis:Â
- cells oblong-elliptical to broadly spindle-shaped
- length 130–390 µm, width 40–82 µm
- two chloroplasts with 4–6 ridges
- margins of ridges deeply notched
- 1–2 elongated pyrenoids per chloroplast
- pyrenoids often covered with starch grains
- cell wall smooth
Netrium digitus is one of the most common algae that can be found in bogs and Sphagnum ponds. Netrium digitus often appears in large numbers.
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A characteristic feature of Netrium digitus is its spindle-shaped form with broadly rounded apices. Sometimes the cells are very slightly constricted in the middle. There are two chloroplasts, which are distinctly ribbed. The edges of these ribs are lobed, with the individual lobes further divided into fine projections. The cell nucleus lies centrally between the chloroplasts. Oil-like vesicles and small crystals can often be seen in the cytoplasm.
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Netrium digitus differs from the similar species Netrium oblongum in size, cell shape, and shape of the chloroplast. Netrium oblongum, at 90–155 µm, is only about half as large as Netrium digitus, and the cell shape is more oval. In addition, the outer lobes of the chloroplasts in Netrium oblongum are not further divided.
Fig. 1 a-c: Netrium digitus. L = 217 µm. Three focal planes of a specimen found in May 2026 in the Schwemm Moor (Austria). Note the notches ridges of the chloroplasts. Obj. 60 X.
Fig. 2 a-b: Netrium digitus. L = 217 µm. The same specimen as shown in fig. 1 a-c in brightfield illumination. Obj. 60 X.