Eastern and Southern United States
These collections have been sequenced and are very close to Lactarius yazooensis, but not exactly. So, along with many other collections, they have been given the temporary code Lactarius sp. ‘yazooensis-IN01’. And, as Stephen Russell explains,
“1.) A temp code does NOT imply that a species is new to science nor undescribed. It MAY be undescribed, but a temp code being utilized is making no claim to that effect. The temp code only implies that more work needs to be done on the taxon to be able to properly apply a name.
2.) A temp code does not inherently imply “species” boundaries – although it certainly can delimit them. The general taxonomic analog for the most temp codes is species, but temp codes are also used to annotate work that needs to be done at infraspecific ranks – subspecies, varieties, forms. Sometimes they annotate sequence variants that will need to be conflated as we get more data. I think of temp codes as most frequently representing a taxon at some taxonomic rank (typically species), which needs further work to resolve, rather than all of them being a “species” by default.”
Here is Alexander Smith’s description of Lactarius yazooensis:
Pileus 5-15 cm broad, convex-depressed, the margin inrolled and
at first minutely pubescent, soon becoming broadly infundibuliform and
margin naked, surface viscid, glabrous, zonate (conspicuously so),
the darker zones orange-ochraceous to rusty orange or dull orangered, gradually becoming paler and more ochraceous, in age with
cinnamon-buff and paler zones alternating. Context firm and rigid,
pallid, unchanging, taste excruciatingly acrid. Latex milk-white, unchanging, exceedingly acrid, copious.
Lamellae crowded, moderately broad finally, adnate becoming
decurrent, pallid to pale vinaceous-cinnamon at first, passing through
vinaceous-cinnamon tones to near “fawn color” (~ vinaceous), slowly
staining brownish.
Stipe short thick and hard, 2-6 cm long, 1-2.5 cm thick, surface
dry, + equal, whitish to pallid or in age somewhat discolored.
Spore deposit buff-yellowish….”.
“Observations.-The horribly acrid taste, changing color of the
gills from pallid to dull vinaceous by old age, unchanging latex, and
(so far at least) no (or very few) scrobiculi on the stipe, distinguish it.”
Lactarius sp. ‘yazooensis-IN01’ may be a variant of Lactarius yazooensis or a new species. Worth noting, from having the luxury of looking at 75 sequenced collections on iNaturalist with four of my own, they differ from Smith’s description in being paler (almost white), having heavy pitting (scrobiculi) and, in my experience, some have a mild taste.
Name comes from having been first described from Yazoo, Mississippi.
Resources:
North American species of Lactarius, p. 264, University of Michigan Library Digital Collections, University of Michigan Herbarium Fungus Monographs
iNaturalist observations of Lactarius sp. ‘yazooensis-IN01’