Sagittaria

Fruits and male flowers are often necessary for positive determination of these highly variable aquatics.

1. Sepals closely appressed; pedicels thick (the lower ca. 3–5 mm in diameter); leaves very broadly sagittate, much broader than long; lowermost flowers mostly bisexual.

S. montevidensis

1. Sepals of mature pistillate flowers reflexed; pedicels more slender; leaves various; lowermost flowers ordinarily pistillate.

2. Filaments pubescent with ± flattened or scale-like hairs; leaves not sagittate (or small basal lobes occasionally present in S. rigida).

3. Pistillate (lower) flowers sessile or nearly so; axis of the inflorescence strongly bent above the lowest flowers; achenes with beak ca. 1–1.5 mm long.

S. rigida

3. Pistillate and staminate flowers pediceled; axis of inflorescence straight; achenes with beak ca. 0.2–0.8 mm long.

4. Achenes with beak 0.4–0.6 mm long; anthers clearly shorter than the filaments.

S. cristata

4. Achenes with beak minute, scarcely discernable, ca. 0.2 mm long; anthers as long as or longer than filaments.

S. graminea

2. Filaments glabrous; leaves usually sagittate when emersed.

5. Mature achenes with a ± horizontal beak projecting to one side and attaining 0.5–1.5 (–2.3) mm in length; faces of achene not winged, at most with a visible resin duct; bracts 4–9 mm long (or up to 11 mm in some robust plants).

S. latifolia

5. Mature achenes with an erect or curved apical beak up to ca. 0.7 mm long; faces of achene sometimes with a low wing or ridge; bracts usually (8–) 10–16 mm long.

6. Achenes with beak ca. 0.4–0.7 mm long, appearing as a continuation of the ± straight margin of the achene, straight or curved outward or over apex of achene.

S. brevirostra

6. Achenes with a very tiny erect beak scarcely 0.2–0.3 mm long, terminating a swollen or convex margin of the achene and thus appearing to project from summit of the achene, definitely set in from the margin.

S. cuneata

All species found in Sagittaria

Sagittaria brevirostraSHORT-BEAKED ARROWHEAD 
Sagittaria cristataCRESTED ARROWHEAD 
Sagittaria cuneataARUM-LEAVED ARROWHEAD 
Sagittaria gramineaGRASS-LEAVED ARROWHEAD 
Sagittaria latifoliaWAPATO, DUCK-POTATO, COMMON ARROWHEAD 
Sagittaria montevidensisARROWHEAD 
Sagittaria rigidaSTIFF ARROWHEAD 

Citation:

MICHIGAN FLORA ONLINE. A. A. Reznicek, E. G. Voss, & B. S. Walters. February 2011. University of Michigan. Web. December 13, 2017. http://michiganflora.net/genus.aspx?id=Sagittaria.