Green Wood Cup

Green Wood Cup, also called Green Elfcup and when growing on oak called Green Oak, is a common small fungus. It occurs in Europe, Asia, North America, South America, and Australia. In the United States it occurs east of the Great Plains and west of the Sierra Nevada and Cascade Mountain Ranges but mostly absent from the remainder of the country. It is common but often overlooked due to its small size and because it infrequently produces fruiting bodies. It is common in Minnesota. It is found in woodlands on dead barkless twigs and branches of mostly hardwoods, especially oak, but also of conifers.

Green Wood Cup produces fruiting bodies infrequently. It most often appears as a bluish-green stain on well-rotted wood. When present, the fruiting body is a small, saucer-shaped cap with a tiny stalk.

The cap is ⅛″ to 5⁄16″ (3 to 8 mm) in diameter. It is cup-shaped at first but as it matures it flattens out and the edges become wavy. The upper, fertile surface is hairless and bluish-green, sometimes becoming tinged yellow with age. The outer surface is hairless and bluish-green.

The stalk is usually ⅛″ to ¼″ (3 to 6 mm) long, sometimes longer, and 1⁄32″ to 1⁄16″ (1.0 to 1.6 mm) thick. It is the same color as the outer surface of the cap. It is usually off-center, sometimes centered.

The flesh is thin and bluish-green. It may be edible but is too insubstantial to try.

Turquoise Elfcup (Chlorociboria aeruginosa) is turquoise colored and smaller but otherwise almost identical in appearance. The stalk is shorter and is usually centered. The flesh is orangish-yellow. It also occurs in Minnesota but is much less common.

Mostly hardwoods, especially oak, but also of conifers.

Summer through fall