A leafless autumn bloom
In the deciduous forests of eastern North America, a strange orchid appears as other plants are fading. Corallorhiza odontorhiza, the Autumn Coralroot, sends up a slender, leafless stalk from late August to October. The stem, ranging from yellow-green to a purplish-brown, reaches heights of 10 to 30 centimeters. It has no green leaves because it does not perform photosynthesis. Instead, it is a mycoheterotroph, a plant that derives its nutrients from fungi in the soil.
The orchid forms a parasitic relationship with fungi from the Tomentella genus. These fungi, in turn, have a symbiotic relationship with surrounding trees like oaks and pines. The Autumn Coralroot essentially hijacks this network, stealing nutrients the fungus has drawn from the trees. Its own root system is a branched, coral-like rhizome that gives the genus its name—Corallorhiza combines the Greek "corallion" (coral) and "rhiza" (root). The specific name, odontorhiza, means "tooth-root," referring to the tooth-like swollen base of the flowering stem.
The self-pollinating flower
A peculiar feature of the Autumn Coralroot is its reproductive strategy. The species produces two distinct types of flowers. The more common form, designated C. odontorhiza var. odontorhiza, has cleistogamous flowers. These flowers never truly open, remaining as small, closed buds about 6-8 mm long. Inside these closed blossoms, the orchid self-pollinates. This strategy guarantees reproduction without the need for external pollinators. The flower's ovary begins to swell into a seed capsule almost as soon as the stem emerges from the ground.
A rarer form, C. odontorhiza var. pringlei, produces chasmogamous, or open, flowers. These flowers have a more typical orchid appearance, with a white lower lip often marked with two purple spots. While these open flowers seem to invite insect pollination, no specific pollinators have been identified. Experiments show that when insects are excluded, these open flowers have very low seed set, confirming their dependence on pollinators. The cleistogamous form, however, ensures the continuation of the species by taking no chances. After a hard frost, the drooping capsules, each 5 to 8.5 mm long, split open to release their dust-like seeds to the wind.