Lilium

1. Flowers erect; tepals distinctly narrowed at the base to a slender claw; leaves up to 8 (–14) mm wide.

L. philadelphicum

1. Flowers nodding (fruit becoming erect); tepals narrowed gradually toward base, not clawed; widest leaves 8–35 mm wide.

2. Flowers pink or purple.

L. martagon

2. Flowers orange.

3. Tepals glabrous within; stem glabrous above; leaves mostly whorled.

L. michiganense

3. Tepals with pubescent strip basally within; stems with cobwebby pubescence, especially above; leaves alternate but crowded.

L. lancifolium

All species found in Lilium

Lilium lancifoliumTIGER LILY 
Lilium martagonMARTAGON LILY 
Lilium michiganenseMICHIGAN LILY 
Lilium philadelphicumWOOD LILY 

Citation:

MICHIGAN FLORA ONLINE. A. A. Reznicek, E. G. Voss, & B. S. Walters. February 2011. University of Michigan. Web. March 25, 2017. http://michiganflora.net/genus.aspx?id=Lilium.