Specimens in flower should have the sepals and petals measured when fresh, or be carefully pressed to make sure they do not shrivel; mature fruits are best for positive identification. The Eurasian Alisma plantago–aquatica differs from both our native species in apparently having a straight, long style ca. 0.6-1.5 mm long and longer than the ovary at anthesis, and narrowly ellipsoid anthers 0.7-1.4 mm long. Our two species have ± curved styles only 0.2-0.6 mm long and usually shorter than the ovary, and ovoid anthers 0.4-1 mm long. Alisma plantago-aquatica is said to have purplish-pink petals, though some collections note white. Also, the normally white Michigan species may have the petals pink distally, as in collections of A. triviale from Lenawee Co. Alisma gramineum is known from the Ontario shore of Lake Huron and eastward. It appears to be increasing in abundance, and may eventually be found in Michigan. It has narrow, linear-lanceolate or narrowly elliptic blades ca. 3–5 times as long as wide (the submersed ones being ribbon-like) and pale pink or pink-purple flowers, in contrast to the ovate to elliptic blades less than 3 times as long as wide and usually white flowers of our two species.
1. Achenes 1.5–2 mm long; larger fruiting heads 3–4 mm in diameter (excluding sepals).
1. Achenes 2.2–3 mm long; larger fruiting heads 4–7 mm in diameter (excluding sepals).
All species found in Alisma
MICHIGAN FLORA ONLINE. A. A. Reznicek, E. G. Voss, & B. S. Walters. February 2011. University of Michigan. Web. December 11, 2017. http://www.michiganflora.net/genus.aspx?id=Alisma.