Russula viridirubrolimbata

Russula viridirubrolimbata is immediately recognisable by its bicoloured cap.

Cap

The centre is olive-green to grass-green while the outer zone and margin are distinctly reddish to blood-red, creating a sharply contrasted green-on-red pattern unique among common Yunnan market russulas.

The cap is 5-12 cm, convex to broadly flattening and slightly depressed with age. The surface is dry in typical conditions, slightly viscid when wet, and the cuticle peels a third of the way inward.

Gills

The gills are white to cream, moderately crowded, and brittle - run a finger across them and they crumble or snap exactly like chalk. This is the universal russula characteristic, distinguishing them from the flexible, greasy gills of Russula cyanoxantha and, crucially, from the free, non-brittle gills of any deadly Amanita.

Stem

The stem is white, firm, 4-9 cm tall, with no ring and no volva whatsoever at the base.

Flesh

Flesh white, firm, unchanging on exposure to air or cutting, with a mild, slightly nutty taste.

Spore print white to pale cream.

A forest species of the warm-temperate to subtropical montane zone, found in the pine-oak and mixed broadleaved forests characteristic of Yunnan province at 1500-2800 m elevation.

It is ectomycorrhizal, meaning it forms an obligate underground partnership with the roots of living trees - primarily oaks (Quercus), stone oaks (Castanopsis, Lithocarpus) and Yunnan pine (Pinus yunnanensis). As a result it always grows on the forest floor beneath or near these trees, never on dead wood.

It favours the well-drained but moisture-retaining red and yellow clay soils of the Yunnan highlands.

The fruiting season coincides precisely with the East Asian summer monsoon. In Yunnan this means heavy rains from June onwards, and the mushroom fruits prolifically from late June through September, with stragglers into October as rains taper.

It is a warm-season species: cool or dry conditions suppress fruiting entirely. Peak market availability in Yunnan is July and August.

Grows singly or in scattered individuals on the forest floor, never clustered or in tight rings, and never on wood.

New fruit bodies appear within about one week of heavy monsoon rains once the soil has warmed to at least 15 °C.

Because it is mycorrhizal it will not grow away from its host trees - finding it in the open or on cultivated land would be a strong signal that something is wrong with the identification.

Monsoon-driven: fruits after sustained heavy rainfall when soil temperatures reach 15-24 °C. Ectomycorrhizal with oaks, Castanopsis and Yunnan pine in montane forest. New fruit bodies appear roughly 5-10 days after a soaking rain.

The most dangerous confusion is not with another russula but with a deadly Amanita.

Several green-tinged or bicoloured Amanita species grow in the same Yunnan forests, most notably Amanita phalloides s.l. and related amatoxin-containing species. These have:

• A membranous volva at the stem base
• Usually a ring on the stem
• Free (not attached) gills
• Fibrous (not chalky) flesh

The bicoloured green-to-red cap of R. viridirubrolimbata is distinctive within the genus, but a hasty picker could overlook the colour pattern and simply see 'a white-gilled woodland mushroom', at which point the base of the stem becomes the sole safety check.

Within the genus Russula, the dangerous confusion is with Russula subnigricans, which causes rhabdomyolysis (severe skeletal muscle breakdown) and is lethal.

R. subnigricans is a dull brownish-white to greyish mushroom without the striking green-red bicolour, and its flesh slowly reddens then may darken when cut - but both features require careful observation, and the two species share the same forest and fruiting season.

Any russula in Yunnan whose flesh reddens when broken should be treated as potentially R. subnigricans and must not be eaten.

Other russulas with reddish cap tones (e.g. Russula sanguinea, R. emetica-group species) are acrid and peppery - a chewed-and-spat taste test would confirm acridity - but acridity alone does not indicate safety, and many look-alike species should simply be left alone unless verified by an expert.

When harvesting, always extract the full stem by gently rotating and lifting, or by digging carefully with a knife, so that the very base of the stem is exposed.

This step is not optional: it is the only way to confirm the absence of a volva (membranous sac or girdled bulb at the base), which - if present - would indicate a deadly Amanita rather than a russula.

Confirm that:

• The gills are brittle and crumbling (not flexible or greasy)
• The stem is solid-to-hollow and white (not fibrous)
• There is no ring

Choose young to middle-aged specimens; old ones become soft, watery and attractive to larvae. Transport in a breathable container.

If any feature does not match - especially a volva, a ring, or gills that do not snap - discard the specimen and seek expert advice.

Prepared in the standard Yunnan style:

• Stir-fried with garlic, chili and oil
• Added to hot-and-sour soups
• Sauteed in a mixed mushroom dish with other forest finds

The firm, mild flesh holds texture well during cooking. Fully cook the mushroom through - it should never be eaten raw or only lightly heated.

The mild taste makes it a background player rather than the star of a dish; it benefits from bold seasoning.

Store fresh specimens in a breathable bag in the refrigerator and use within two days.

Russula viridirubrolimbata is regarded as an edible species and is sold in the Yunnan wild mushroom markets. It is not among the premium-priced elite (such as Matsutake, boletes, or the highly prized Russula griseocarnosa and R. virescens), but it is collected and consumed without reported problems when properly identified.

The safety case rests entirely on correct identification. The distinctive bicoloured green-red cap is the primary field character, and it must be backed up by confirming:

• Brittle gills
• White, unchanging flesh
• No ring
• Critically, no volva at the stem base

The lethal amatoxins in Amanita phalloides cause a clinically silent latency period of 6-24 hours before liver failure; the mild taste means no warning is given at the time of eating.

Never eat a white-gilled woodland mushroom without inspecting the full stem base.

Additionally, never eat any wild Russula raw - mild-tasting russulas, including this species, can cause gastrointestinal upset when raw and should always be cooked thoroughly.