Compare Achnanthidium delmontii
Compare
Achnanthidium delmontii is very similar to A. pyrenaicum. In fact, some specimens and populations of these two species may be indistinguishable under LM.
The main differences are in valve shape, which is linear-elliptic with rounded ends in A. delmontii and lanceolate, with more narrow pointy apices in A. pyrenaicum. The valves are, on average, wider in A. delmontii. The striae are almost parallel in the central part of the raphe valve in A. pyrenaicum, while they are often slightly curved and radiate in A. delmontii. The central area on the raphe valve of A. delmontii is usually wider than in A. pyrenaicum.
Achnanthidium deflexum is similar in valve dimensions, but has slightly more set-off valve apices and a small central area on the raphe valve. While both A. pyrenaicum and A. deflexum usually have dash-like (transapically elongated) areolae on the raphe valve, A. delmontii has small rounded areolae (not visible with LM). Small rapheless valves of A. delmontii could be difficult to distinguish from A. rivulare or A. crassum, but raphe valves of the latter two species lack fascia.
LM scalebar = 10 µm
Length Range
5.6-22.5 µm
5.6-22.5 µm
Width Range
3.5-5.2 µm
3.5-5.2 µm
Striae in 10 µm
20-26 in the center, up to 35 at the ends of raphe valve; 18-22 in the center, up to 25 at the ends of rapheless valve
20-26 in the center, up to 35 at the ends of raphe valve; 18-22 in the center, up to 25 at the ends of rapheless valve
Achnanthidium pyrenaicum
Length Range
10–16 µm
10–16 µm
Width Range
2.5-4.0 µm
2.5-4.0 µm
Striae in 10 µm
20-25 in the center, 34-40 at the raphe valve ends; 20-28 in the center, 32-38 at the rapheless valve ends
20-25 in the center, 34-40 at the raphe valve ends; 20-28 in the center, 32-38 at the rapheless valve ends
Achnanthidium deflexum
Length Range
7.4-28.3 µm
7.4-28.3 µm
Width Range
3.1-5.3 µm
3.1-5.3 µm
Striae in 10 µm
15-28 in the middle of raphe valve
15-28 in the middle of raphe valve
Achnanthidium rivulare
Length Range
5.4-23.8 µm
5.4-23.8 µm
Width Range
2.6-4.4 µm
2.6-4.4 µm
Striae in 10 µm
19-25 in the middle of raphe valve, 19-28 in the middle of the rapheless valve
19-25 in the middle of raphe valve, 19-28 in the middle of the rapheless valve
