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Corallorhiza

The plants of this genus are essentially lacking in chlorophyll and basically parasitic on fungi inhabiting their characteristic coral-like masses of rhizomes. The species are almost always easily distinguished in the field, although the presence of uncommon color variations makes the key necessarily more complex. Case (1987) notes Corallorhiza wisteriana Conrad from northern Illinois and Indiana, and it should be looked for in southwestern Michigan. It resembles C. odontorhiza, but blooms in the spring, lacks a bulbous base to the stem, and has a larger lip.

1. Lip with a small lobe or elongate tooth on each side near the base (sometimes difficult to see in dried specimens).

2. Sepals and petals 3-nerved; summit of ovary with a low protuberance (like a rudimentary spur) usually visible below the base of the lip; lip 4.5–7 mm long.

C. maculata

2. Sepals and petals 1-nerved (or the latter rarely weakly 3-nerved); summit of ovary without visible protuberance; lip 2.5–4.5 (–5) mm long.

C. trifida (in part)

1. Lip entire, or merely denticulate or erose.

3. Sepals and petals 3–5-nerved, 8–15 mm long, conspicuously striped with purple, the lip solid purplish apically.

C. striata

3. Sepals and petals 1-nerved (or faintly 3-nerved), less than 6 mm long, not conspicuously striped.

4. Perianth 3–4.5 mm long, purplish; lip white, spotted with purplish; mostly in southern Michigan, in upland woods; flowering August–September.

C. odontorhiza

4. Perianth 4–5.5 mm long, yellowish; lip unspotted white (or sometimes spotted in northern Michigan); found throughout Michigan but more common northwards, often in swamp forests; flowering in southern Michigan April–June (sometimes later northward).

C. trifida (in part)

All species found in Corallorhiza

Corallorhiza maculataSPOTTED CORAL-ROOT 
Corallorhiza odontorhizaFALL CORAL-ROOT 
Corallorhiza striataSTRIPED CORAL-ROOT 
Corallorhiza trifidaEARLY CORAL-ROOT 

Citation:

MICHIGAN FLORA ONLINE. A. A. Reznicek, E. G. Voss, & B. S. Walters. February 2011. University of Michigan. Web. October 23, 2017. http://michiganflora.net/genus.aspx?id=Corallorhiza.