Orange Pinwheel

Marasmius siccus belongs to a genus of small, tough-fleshed litter fungi (family Marasmiaceae) whose members are famous for shrivelling in dry weather and reviving almost unchanged when rain returns. The species is one of the most colourful of the North American "pinwheels", named for the way the deeply grooved cap looks like a child's paper pinwheel seen from above.

Because of its bright colour and habit of fruiting in scattered troops after summer storms, it is one of the first small fungi that beginners learn to recognise in eastern woodlands. Despite the delicate look, the tissue is remarkably tough and pliant rather than brittle.

The genus name refers to this withering-and-reviving habit, and the specific epithet siccus means dry, a nod to the dry, non-sticky cap surface.

Cap

The cap is 5-25 mm across, convex to bell-shaped, dry, and coloured a strong rusty orange, burnt orange or apricot, sometimes paler toward the margin. Deep radial grooves divide the surface into pleats that run from the margin to a small, often slightly darker central depression.

Gills

Gills are white to pale cream, contrasting sharply with the cap, broad and widely spaced, and are attached narrowly to the stem or nearly free. Crucially, they attach directly rather than to a raised collar encircling the stem.

Stipe

The stem is 2-7 cm long but barely a millimetre thick, wiry, smooth and shining, whitish or pale at the very apex and shading to dark reddish brown or black over most of its length. It arises directly from a leaf or twig with no cottony pad of mycelium at the point of attachment.

Flesh and spore print

The flesh is thin, tough and pliable, and the whole mushroom revives after drying. The spore print is white, and the spores are long and club- or pip-shaped under the microscope.

The Orange Pinwheel fruits on fallen leaves, leaf petioles and small twigs of hardwoods, with oak, beech, maple and hickory litter especially favoured. It usually appears scattered rather than clustered, often dozens of caps spread across a patch of damp litter after summer rain.

It is common through eastern North America from summer into early autumn, and closely comparable populations are recorded in East and Southeast Asia. Damp, shaded deciduous or mixed woodland with a deep leaf layer is the typical setting.

This is a litter saprotroph. Its mycelium runs through fallen leaves and fine woody debris, breaking down cellulose and contributing to the rapid turnover of the forest floor's uppermost layer; heavily colonised leaves become bleached and papery.

The tough, drought-resistant fruit body is an adaptation to the exposed litter surface: rather than rotting during a dry spell, the mushroom shrivels, then rehydrates and continues releasing spores when rain returns, spreading spore release across many weeks.

Marasmius fulvoferrugineus is very similar but averages larger, with a duller tawny to rusty brown cap and more widely separated gills. Marasmius pulcherripes is rose-pink to reddish purple rather than orange. Marasmius rotula, the Collared Parachute, has a whitish to pale buff cap and, decisively, gills that attach to a free collar ringing the stem instead of to the stem itself.

Marasmius capillaris is smaller and pale, growing on individual oak leaves on a hair-like stem. Small orange Mycena species can be mistaken at a glance, but their caps are smoother and only finely lined, their flesh is brittle rather than pliant, and they collapse instead of reviving after drying.