Frost’s Amanita (Amanita frostiana)

🏷️ Description

Amanita frostiana, or Frost’s amanita, is a striking small mushroom native to the mixed forests of eastern North America, especially the Northeastern U.S. and Southeastern Canada. 🌳🌲 Often found from June to September, it thrives in hardwood and coniferous forests, particularly among hemlock pine duff and near Quercus oaks and Pinaceae conifers.

🌈 Appearance: This vibrant fungus sports a bright yellow to orange cap sprinkled with white, yellow, or orange warts. Starting as a cute little dome, the cap eventually flattens as it matures. Underneath, you’ll find white to cream-colored gills, while its pale to bright yellow stem stands tall, complete with a white to pale yellow volva at the base.

⚠️ Edibility: UNKNOWN & potentially poisonous! ☠️ So, admire its beauty, but don’t snack on it.

🧪 Fun Fungal Facts:

• Its spores show a negative amyloid reaction with Melzer’s reagent, helping mycologists tell it apart from lookalikes like A. flavoconia.

• Though primarily North American, a 1962 sighting in Thailand sparked debate — but it was likely the similar A. rubrovolvata. 🌏

🔎 Identification

🧢 Cap:

• Shape: Convex or shield-shaped, flattening with age

• Size: 1–3 inches (2–8 cm) wide

• Color: Yellow to golden orange, sometimes scarlet or deep reddish-pink

• Texture: Smooth, slightly sticky when moist

• Margin: Distinctly lined as the cap matures

📏 Stem:

• Length: 2–2.5 inches (4.7–6.2 cm)

• Width: 4–11 mm

• Color: Pale to bright yellow

• Features: Persistent annulus (ring). Universal veil leaves yellow to cream flakes or powder at the base.

🍃 Gills:

• Attachment: Free from the stem

• Color: White to cream-colored

• Spacing: Close to crowded

• Short Gills: Truncate to excavated-truncate

🔬 Spores & Microscopy:

• Shape: Globose to subglobose

• Size: 7.0–10.2 μm wide

• Reaction: Inamyloid (does not turn black with Melzer’s reagent)

🌍 Habitat & Distribution:

• Native to eastern U.S. and southeastern Canada

• Grows in mixed forests with Quercus oaks and Pinaceae conifers

• Often found in hemlock pine duff

• Fruiting Season: June to September

👀 Look-Alikes

🍄 Amanita rubrovolvata

• Similar reddish-orange cap

• Thailand reports were likely this species, not A. frostiana

• Found in Asia, not native to North America

🍄 Amanita subfrostian

• Found in southwestern China

• Paler cap compared to A. frostiana

• Shares similar habitats but differs in regional distribution

🍄 Amanita flavoconia

• Common misidentification due to similar cap coloration

• Can be distinguished microscopically (has amyloid spores vs. A. frostiana’s inamyloid spores)

🍄 Amanita albocreata

• Found in northeastern U.S., southeastern Canada, and Newfoundland

• Known for its stark white bulb and yellow-white collar

• Shares hardwood-hemlock habitats

🍄 Amanita muscaria var. muscaria

• The iconic “fly agaric” with its bright red cap and white warts

• Psychoactive and toxic

• Related through microscopic features (clamps at basidia bases)

📜 Synonyms

• Agaricus muscarius var. minor Peck

• Amanita macrospora H. L. Stewart & Grund

• Amanitaria frostiana (Peck) E.-J. Gilbert

Photo sources:

Photo 1 - Author: Dan MacNeal (CC BY 4.0)

Photo 2 - Author: Jaime McGuigan (CC BY 4.0)

Photo 3 - Author: Eli T. (CC BY 4.0)

Photo 4 - Author: Eli T. (CC BY 4.0)

Photo 5 - Author: Larry Jensen (CC BY 4.0)