Lythraceae

Many species in this family are noted for dimorphic or trimorphic flowers, that is, with styles and stamens of various lengths (e.g., long styles and short stamens or vice versa), thus helping to ensure cross-pollination. The calyx lobes (in our species) alternate with appendages, as in many Rosaceae. The ovary is free from the perigynous floral tube and hence is superior.

1. Calyx with 4 teeth or shallow lobes slightly exceeding the appendages; plant at maturity ± sprawling in habit, less than 4 dm tall.

2. Flowers and fruits mostly clustered in the axils; leaves cordate-clasping at the base.

Ammannia

2. Flowers and fruits solitary in the axils; leaves (at least middle and upper ones) tapered to the base.

Rotala

1. Calyx with 5–6 (–7) teeth or lobes distinctly shorter (and broader) than the appendages; plant at maturity erect or high-arching, only rarely less than 4 dm tall.

3. Floral tube bell-shaped (about as broad as long, excluding the calyx lobes); flowers mostly in distinct axillary clusters (not appearing crowded terminally); leaf blades tapered to a short petiole.

Decodon

3. Floral tube elongate (at least twice as long as broad); flowers (though axillary) often crowded in dense terminal inflorescences; leaf blades sessile or even clasping.

Lythrum

Citation:

MICHIGAN FLORA ONLINE. A. A. Reznicek, E. G. Voss, & B. S. Walters. February 2011. University of Michigan. Web. August 19, 2017. http://michiganflora.net/family.aspx?id=Lythraceae.