Identification of species in Lactarius ranges from very easy to very difficult. Over 200 species have been described from North America, and the authoritative monograph (Hesler & Smith, 1979; see below) is a bear to work with. "Lactariologists" have developed a suite of characters that are used in Lactarius identification--but many of these characters demonstrate considerable variability, so you will definitely need to collect several fresh mushrooms, representing different stages of development, to get very far in identifying most of the milky caps. Especially important in traditional Lactarius identification is the color of the milk, and any color changes in the milk after it is exposed to air. Additionally, Lactarius milk frequently stains the gills or flesh of the mushroom, and the color of staining reactions can be critical to identification. Slice your Lactarius specimen in half and damage the gills with your knife point in order to observe the milk and any staining reactions. Patience is often required to observe staining, however, since reactions can take up to an hour to develop.
Contemporary Lactarius studies, armed with evidence from DNA analysis, have begun to elucidate the murky picture of North American Lactarius species previously painted with morphological analysis; in particular, the species with colored milk (forming section Deliciosi) have been recently investigated and described (Nuytinck and collaborators, 2006). The bulk of the genus, however, remains to be studied with contemporary methods. I suspect that specific mycorrhizal association will eventually turn out to be a much more important identification character than it has been in the past, and I recommend that anyone collecting Lactarius specimens for scientific study take pains to thoroughly document the trees and woody plants in the collection site (see this page for help with this effort).
(Incomplete) Key to (about 50) North American Lactarius Taxa
NOTE: This key is incomplete; it is a work in progress. It currently treats some of the trufflelike and "malformed" species (formerly known as species of Arcangeliella); the species with colored milk (section Deliciosi); the small group of funky species centered around Lactarius sordidus; and those species possessing milk that turns yellow on exposure to air (not a natural group of related species, but a handy grouping for identification). Well over 100 North American species not belonging to these groups remain untreated. An extensive references list follows the key.
| 1. | Found primarily in western North America; growing underground, trufflelike--or growing above ground, mushroomlike but with gills poorly formed ("Archangeliella"). | 2 |
| 2. | Growing more or less completely underground. | 3 |
| 2. | Growing primarily above ground. | 5 |
| 3. | Outer surface reddish brown to brown, discoloring and staining green. | |
| 3. | Outer surface differently colored; not discoloring green. | 4 |
| 4. | Mushroom usually measuring 1 cm or less across; surface pinkish to orangish or pinkish brown; spores 5.5-8 µ long. | Arcangeliella saylori |
| 4. | Mushroom up to 3 cm across; surface whitish to yellowish; spores 7.5-9.5 µ long. | Arcangeliella parva |
| 5. | Milk staining tissues brown to reddish; cap brownish. | |
| 5. | Milk not staining tissues; cap variously colored. | 6 |
| 7. | Cap 2-3 cm across, pale yellowish; spores elliptical. | Arcangeliella lactarioides |
| 7. | Cap 4-8 cm across, dull olive with yellow spots; spores round or nearly so. | |
| 8. | Cap color varying from yellowish to orangish or bluish (especially when young), discoloring green and becoming often sordid green overall at maturity; milk scant, yellowish to brownish or vaguely bluish (but not orange); gills crowded, yellowish before discoloring greenish; stem without potholes; spores 7-9 x 5-7 µ, with scattered connecting lines forming, at most, partial reticula; found under conifers in eastern North America. | |
| 8. | Not completely as above. | 9 |
| 9. | Milk colored as exuded (slice young specimens and check the flesh in the stem apex and near the gills); green stains often developing on surfaces. | 10 |
| 9. | Milk watery, white or whitish as exuded--sometimes becoming yellow or yellowish after exposure to air; green stains rarely developing (though cap and stem may be colored green, or milk may dry faintly greenish). | 21 |
| 10. | Fresh cap whitish or buff (aside from staining). | 11 |
| 10. | Fresh cap more highly colored. | 13 |
| 11. | Gills bright salmon orange before staining; distributed in the southeastern United States and in Mexico. | |
| 11. | Gills yellowish to orangish before staining. | 12 |
| 12. | Western in distribution; growing under pines; milk red; stem without potholes. | |
| 12. | Known from Florida; growing under pines or oaks; milk orange; stem with potholes (cap whitish when young; later often yellowish to pinkish before staining). | |
| 13. | Associated with Northern White-Cedar in northeastern North America; cap orange; green staining and bruising absent throughout development. | |
| 13. | Range and mycorrhizal associations various; cap colors various; green stains developing, at least by maturity. | 14 |
| 15. | Fresh cap pinkish to purplish pink; milk red to purple-red. | 16 |
| 15. | Not completely as above. | 17 |
| 16. | Associated primarily with Eastern Hemlock in northeastern and eastern North America; spores 8-11 µ long. | |
| 16. | Associated with pines (species of Pinus); known from the Veracruz region of Mexico; spores 7-8 µ long. | Lactarius miniatosporus |
| 18. | Western in distribution; associated with pines (species of Pinus) or with Douglas-fir; gills orange or orangish before discoloring; cap brownish orange. | |
| 18. | Southern and eastern in distribution; associated with pines or with oaks; gills pinkish before discoloring; cap bluish to greenish or grayish, usually with a silvery sheen. | |
| 19. | Known from Florida under pines and oaks; cap pale, becoming yellowish; spores 7-9 µ long. | |
| 19. | Not as above; cap more or less orange, spores slightly or substantially longer than above, range and mycorrhizal associations various. | 20 |
| 20. | Known from California in association with spruce; cap small (2-5.5 cm across); green staining extensive; basidia, basidioles, and cystidia with dark contents. | Lactarius aurantiosordidus |
| 20. | Range and mycorrhizal association various; cap generally larger than above when mature; green staining slight or extensive; hymenial elements lacking dark contents. | |
| 21. | Cap dark green, olive, brown, or olive brown; KOH producing a magenta reaction on cap surface; stem with potholes. | 22 |
| 21. | Not completely as above. | 24 |
| 22. | Found in eastern North America in association with hardwoods (especially oaks); cap green; fresh gills pinkish. | |
| 23. | Western in distribution; cap olive; spores 7-10 x 6-9 µ, with ornamentation over .5 µ high. | |
| 23. | Widely distributed; cap yellow brown to brown, with olive hues; spores 5.5-7.5 x 5.5-6.5 µ, with ornamentation generally shorter than above. | |
| 24. | Milk white or creamy as exuded but changing quickly (within 30 seconds) to yellow (the milk itself changing color, independently of color changes, including yellowing, in tissues; if uncertain, try isolating the milk on white paper). | 25 |
| 24. | Milk watery, white, or creamy as exuded, not changing quickly to yellow (but possibly becoming slightly and/or slowly yellowish, or changing to another color). | 56 |
| 25. | Fresh, young cap white, whitish, or nearly so--sometimes developing pinkish or yellowish hues. | 26 |
| 25. | Fresh, young cap more highly colored. | 33 |
| 26. | Associated with birch (possibly also with aspen) or northern/montane conifers; young cap margin often bearded or hairy. | 27 |
| 26. | Associated with oaks (possibly with other hardwoods) in eastern, oak-based forests; young cap margin not bearded or hairy. | 30 |
| 27. | Cap with pinkish hues. | 28 |
| 27. | Pinkish hues absent from cap. | 29 |
| 28. | Spores 8-11 x 6.5-8 µ. | |
| 28. | Spores 6.5-8 x 5.5-6.5 µ. | |
| 29. | Stem without potholes or with a few vague spots at maturity; pleurocystidia not projecting substantially beyond basidia. | |
| 29. | Stem with prominent potholes; pleurocystidia projecting. | |
| 30. | Stem without potholes. | 31 |
| 31. | Cap and stem with a downy, sub-velvety feel; gills bruising and discoloring cinnamon to brownish. | |
| 31. | Neither cap nor stem downy or sub-velvety; gills discoloring or not. | 32 |
| 32. | Milk changing from white to pale yellow; gills crowded, staining yellowish brown; spore print white. | |
| 32. | Milk changing from white to darker yellow; gills close, not staining or spotting; spore print yellowish. | |
| 33. | Associated with Coast Live Oak or Tanoak on the West Coast; cap grayish orange becoming brownish orange. | |
| 33. | Not completely as above. | 34 |
| 34. | Cap pink; young margin bearded; associated with birch. | 28 (above) |
| 34. | Cap not pink; young margin smooth to minutely hairy but not bearded; mycorrhizal associations various. | 35 |
| 35. | Stem without potholes. | 39 |
| 36. | Cap dark reddish brown. | |
| 36. | Cap yellow to orange. | 37 |
| 37. | Associated with hardwoods; distributed east of the Rocky Mountains. | 38 |
| 37. | Associated with conifers; distribution various. | |
| 38. | Cap yellow to yellowish, often with a pinkish center. | |
| 39. | Cap otherwise colored. | 44 |
| 40. | Mature cap small (under 4 cm across), pale tan to yellowish. | |
| 40. | Mature cap small or medium-sized; darker than above. | 41 |
| 41. | Fresh cap dark red-brown to red or dark brown, turning olive with KOH; stem colored like the cap; associated with conifers. | |
| 41. | Not completely as above. | 42 |
| 42. | Mature cap small (under 4 cm across); taste mild; associated with cedar and alder in western North America. | |
| 42. | Mature cap larger than above; taste variable; associated with hardwoods in eastern North America. | 43 |
| 43. | Cap initially brown to brownish, with paler zones, becoming brown overall; taste slowly acrid but sometimes mild in older specimens; sliced flesh staining brownish; gills developing cinnamon to brown spots. | |
| 43. | Cap pinkish tan to brown or cinnamon brown, without zones, from the beginning; taste bitter, then peppery; sliced flesh staining yellow; gills developing brownish spots. | |
| 44. | Gills yellow, distant and thick; cap small (usually under 4 cm across), yellowish olive; apparently southern in distribution. | |
| 44. | Not completely as above. | 45 |
| 45. | Cap otherwise colored. | 49 |
| 46. | Associated with conifers in California and the Pacific Northwest; cap scarlet, fading to orange; spore print yellowish. | |
| 46. | Not completely as above. | 47 |
| 47. | Associated with birch; fresh cap dull orange to rusty orange, 3-8 cm across. | |
| 47. | Mycorrhizal associations various; fresh cap bright orange, variously sized. | 48 |
| 48. | Mature cap 5-10 cm across; found in dry hardwood forests east of the Rocky Mountains; flesh turning yellow (before the milk turns yellow) when sliced; spore print yellowish. | |
| 48. | Mature cap 2-6 cm across; found in wet woods across northern North America; flesh remaining whitish when sliced; spore print white. | |
| 49. | Mature cap small (under about 5 cm across). | 50 |
| 49. | Mature cap larger than above. | 52 |
| 50. | Cap pale tan to yellowish. | |
| 50. | Cap otherwise colored. | 51 |
| 51. | Cap pale when young, becoming brownish red; distribution eastern. | |
| 51. | Cap red, red-brown, or orange-brown, fading with age; distribution western. | |
| 52. | Associated with hardwoods. | 53 |
| 52. | Associated with conifers. | 54 |
| 53. | Flesh turning yellow when sliced (apart from the yellowing milk); taste slowly acrid; spores 6-9 µ long, with ornamentation 1 µ or shorter. | |
| 53. | Flesh remaining white when sliced; taste mild; spores 9-11 µ long, with ornamentation 2-2.5 µ high. | |
| 54. | Cap initially pale (pinkish to pale cinnamon), darkening with age; gills developing pinkish to reddish brown spots; probably eastern in distribution. | |
| 54. | Cap red to reddish brown from the beginning; gills not spotting; distribution various. | 55 |
| 55. | Cap dark brownish red to brown; KOH on cap surface olive; milk staining white paper yellow; widely distributed. | |
| 55. | Cap red to orange-red (not brownish red); KOH reaction not recorded; milk-to-paper reaction not recorded; California and the Pacific Northwest. | |
| 56. | This portion of the key is not yet developed. I apologize to collectors whose milky caps I have not yet covered (there are over 100 species remaining). The Hesler & Smith monograph (1979) is online, for those who are comfortable working with technical mycological treatments. A list of this site's Lactarius pages--many of which are not treated in the key above--is below, followed by an extensive Lactarius references list. | |
L. argillaceifolius
L. argillaceifolius var. megacarpus
L. atroviridis
L. camphoratus
L. chelidonium
L. chrysorrheus
L. controversus
L. deceptivus
L. deliciosus
L. fragilis
L. fumosus
L. gerardii
L. glyciosmus
L. hepaticus
L. helvus
L. hygrophoroides
L. imperceptus
L. indigo
L. lignyotellus
L. lignyotus
L. lignyotus var. nigroviolascens
L. luculentus var. laetus
L. maculatipes
L. olympianus
L. payettensis
L. piperatus
L. psammicola
L. quietus var. incanus
L. repraesentaneus
L. rubidus
L. scrobiculatus
L. subplinthogalus
L. subpurpureus
L. subvellereus var. subdistans
L. subvernalis var. cokeri
L. thyinos
L. uvidus
L. vinaceorufescens
L. volemus
L. xanthogalactus
L. zonarius
References
Arora, D. (1986). Mushrooms demystified: A comprehensive guide to the fleshy fungi. Berkeley: Ten Speed Press. 959 pp.
Bills, G. F. (1986). Notes on Lactarius in the high-elevation forests of the southern Appalachians. Mycologia 78: 70-79.
Coker, W. C. (1918). The Lactarias of North Carolina. Journal of the Elisha Mitchell Scientific Society 34: 1-61.
Desjardin, D. E. (2003). A unique ballistosporic hypogeous sequestrate Lactarius from California. Mycologia 95: 148-155.
Heilmann-Clausen, J., A. Verbeken & J. Vesterholt. (1998/2000). The genus Lactarius. (Fungi of Northern Europe, Vol. 2). Denmark: The Danish Mycological Society. 287 pp.
Hesler, L.R. and Smith, A. H. (1979). North American species of Lactarius. Ann Arbor: U of Michigan P. 841 pp. An online version of this monograph is available here, at the University of Michigan Herbarium.
Kauffman, C.H. (1918). The gilled mushrooms (Agaricaceae) of Michigan and the Great Lakes region, Volumes I and II. New York: Dover. 924 pp. (1971 Reprint.) An online version of this publication is available here, at the Michigan DEQ.
Leuthy, C. S. (1997). Key to species of Lactarius in the Pacific Northwest. Retrieved from the Pacific Northwest Key Council Web site: http://www.svims.ca/council/Lactar.rtf
Methven, A. S. (1985). New and interesting species of Lactarius from California. Mycologia 77: 472-482.
Methven, A. S. (1992). An introduction to the infrageneric classification of Lactarius. McIlvainea 10: 29-40.
Methven, A. S. (1993). Contributions to a study of the North American species of Lactarius. McIlvainea 11: 26-34.
Methven, A. S. (1997). Agaricales of California: Volume 10, Lactarius. Berkeley: Mad River Press, 78 pp.
Miller, S. L. et al. (2001). A molecular phylogeny of the Russulales including agaricoid, gasteroid and pleurotoid taxa. Mycologia 93: 344-354.
Montoya, L. & Bandala, V. M. (2004). Lactarius subgenus Piperites: A new species and a new name. Mycotaxon 89: 47-54.
Nuytinck, J. & A. Verbeken. (2005). Morphology and taxonomy of the European species in Lactarius sect. Deliciosi (Russulales). Mycotaxon 92: 125-168.
Nuytinck, J., S. L. Miller & A. Verbeken (2006). A taxonomical treatment of the North and Central American species in Lactarius sect. Deliciosi. Mycotaxon 96: 261-307.
Nuytinck, J. & A. Verbeken. (2007). Key to the European species of Lactarius sect. Deliciosi. Retrieved from the Russulales News Web site: http://www.mtsn.tn.it/russulales-news/id_deliciosi.asp
Saylor, H. (n.d.). Key to the genus Arcangeliella in California. Retrieved from the MykoWeb Web site: http://www.mykoweb.com/CAF/keys/Arcangeliella_key.pdf
Smith, A. H., Smith, H. V. & Weber, N. S. (1979). How to know the gilled mushrooms. Dubuque, Iowa: Wm. C. Brown. 334 pp.
Thiers, H. D. (1984). The genus Arcangeliella Cav. in the western United States. Sydowia 37: 296-308.
Verbeken, A., et al. (2000). On Lactarius ruginosus and L. romagnesii s. str. In: Associazione Micologica Bresadola, ed. Micologia 2000. Brescia, Italy: Grafica Sette, 569-576.
Zeller, S. M. (1947). More notes on gasteromycetes. Mycologia 39: 282-312.
Cite this page as:
Kuo, M. (2007, September). Lactarius: The milky caps. Retrieved from the MushroomExpert.Com Web site: http://www.mushroomexpert.com/lactarius.html
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