The information in this table was compiled from a number of floras:

bulletBudd's Flora
bulletFlora of Alberta
bulletFlora of the Great Plains
bulletFlora of Canada

Species

Description of Valve

Venosus
(sand)

1.5-4 cm, entire,
almost round with deep sinus, bright red to pink, strongly reticulate-veiny;
0 grains  

Acetosa
(escaped)  

Much larger than achene,
thin & reticulate veiny,
wine col.oured

Acetosella
(rare, dry,
sand, acid)  

1-2 mm long, scarcely enlarged, entire;
Achene becoming exerted;
0 grains;
Joint just below flower

Occidentalis

4-10 mm long, entire to denticulate, reddish-brown, reticulate-veiny;
0 grains;
No joint  

Longifolius
(rare, east)  

4-7 mm long, 5.5-6.5 mm wide, entire to denticulate;
0 grains,
Jointed below middle

Paucifolius
(mountains)  

2.5-4 mm long, becoming reddish;
0-1 minute basal grains

Fennicus

3.5-5 mm long, < 5 mm wide, wavy;
0-1 small grains;
Joint present  

Crispus

3-6 mm long, entire to denticulate;
1-3 large, unequal grains, largest globose, <= ½ length of valve, base at or below valve; 
Jointed below midlength  

Salicifolius, Mexicanus  

2-6 mm long, mostly entire, strongly reticulate;
1-3 grains, ½ to 2/3 long as valve;
Curved pedicels rarely > twice valve length;
Joint present

Orbiculatus
(rare,swamp, boreal)  

5-8 mm long & wide, mostly entire;
3 narrow grains, base above valve, ½ long as valve;
No joint

Stenophylus

3.5-5 mm long & wide, coarsely toothed;
3 ovoid grains ½ long as valve;
Pedicles much longer than valves;
Jointed toward base  

Maritimus

3-7 mm long;
1-6 bristles longer than valve width;
3 grains > ½ long as valve;
Jointed near base