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Achnanthidium pyrenaicum can be distiguished from A. minutissimum by its wider lanceolate valves and by the strongly curved terminal raphe fissures. Achnanthidium deflexum is broader in the center and ends than A. pyrenacium. The valve ends are capitate in A. gracillimum and subrostrate in A. pyrenaicum.

LM scalebar = 10 µm
Achnanthidium pyrenaicum LM5 Achnanthidium pyrenaicum LM3 Achnanthidium pyrenaicum LM1 Achnanthidium pyrenaicum LM4 Achnanthidium pyrenaicum LM2
Length Range
10–16 µm
Width Range
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

Achnanthidium minutissimum

(Kütz.) Czarn. 1994

Achnanthidium minutissimum LM4 Achnanthidium minutissimum LM3 Achnanthidium minutissimum LM7 Achnanthidium minutissimum LM2 Achnanthidium minutissimum LM6 Achnanthidium minutissimum LM1 Achnanthidium minutissimum LM5
Length Range
5.6-20.8 µm
Width Range
1.5-3.3 µm
Striae in 10 µm
25-35

Achnanthidium deflexum

(Reimer) Kingston 2003

Achnanthidium deflexum LM4 Achnanthidium deflexum LM1 Achnanthidium deflexum LM3 Achnanthidium deflexum LM5 Achnanthidium deflexum LM2
Length Range
7.4-28.3 µm
Width Range
3.1-5.3 µm
Striae in 10 µm
15-28 in the middle of raphe valve

Achnanthidium gracillimum

(Meister) Lange-Bert. in Krammer and Lange-Bert. 2004

Altergracillima 8 Ed Ahgrac  Va000071 1B Ed Achnanthidium gracillimum LM2 Ahgrac  Va000071 2A Ed Ahgrac  Va000071 2B Ed Achnanthidium gracillimum LM1 Altergracillima 9 Ed
Length Range
12-21 µm
Width Range
3.0-3.7 µm
Striae in 10 µm
21-25 in the center valve, 36-45 at the valve ends