Spring Fieldcap (Agrocybe praecox)
Spring Fieldcap (Agrocybe praecox)
Spring Fieldcap (Agrocybe praecox) is a tan-capped, ring-bearing mushroom native to temperate Europe and North America, one of the earliest gilled fungi to emerge each spring. It grows independently of living trees, feeding on dead organic matter in woodchip beds, mulch, and garden borders. Researchers prize it for a distinctive enzyme system and a set of newly characterized plant-active compounds called agrocybynes.
Agrocybe praecox (Pers.) Fayod — Family Strophariaceae — Order Agaricales
Spring Fieldcap (Agrocybe praecox) is not a mushroom that makes headlines at the farmers' market — it is too bitter raw and too modest for commercial cultivation. What it is, though, is a genuinely remarkable organism: the type species of its entire genus, a confirmed producer of novel polyacetylene plant-growth regulators, a participant in the DOE's 1000 Fungal Genomes project, and one of the most enzymatically active litter-decomposers ever screened. It arrives in mulched garden beds almost as soon as winter loosens its grip, weeks before most gilled mushrooms dare to fruit — and it carries a serious lookalike warning that every forager and cultivator needs to understand before touching a specimen.
What Is the Spring Fieldcap (Agrocybe praecox)?
Spring Fieldcap (Agrocybe praecox) is a medium-sized saprotrophic (decay-feeding) mushroom in the family Strophariaceae, the same family that contains king stropharia, nameko, and pioppino. Saprotrophic means it eats dead organic matter — it has no relationship with the roots of living trees and requires no host plant to grow. This makes it, in principle, cultivable on simple dead substrate, and it explains why it thrives so vigorously in the woodchip-filled borders of parks and managed gardens.
The species has been known to science since 1800, when Dutch mycologist Christiaan Hendrik Persoon first described it as Agaricus praecox — praecox being the Latin word for "precocious" or "early." That name was prophetic: the Spring Fieldcap consistently emerges before most competing fungi have started to fruit, a phenological trait so reliable it anchors the species' common name in every language that has one. In 1889 Swiss mycologist Victor Fayod used it as the definitive reference point for his newly proposed genus Agrocybe, making it the type species — the biological anchor against which all other Agrocybe species are formally defined.
The defining biology in one sentence: Spring Fieldcap is saprotrophic, which means it requires no living host — instead it colonizes dead lignocellulosic substrate (wood, straw, bark chips) via a powerful enzyme system dominated by manganese peroxidase, a lignin-degrading enzyme that has attracted serious industrial research interest.
The Spring Fieldcap is not a well-known culinary mushroom. Sources consistently describe it as marginally edible at best — the raw flesh is distinctly bitter, and even when cooked the bitterness does not fully disappear. It has a characteristic mealy, flour-like odor that some find appealing and others do not. It is eaten opportunistically in parts of Europe and Japan (where it is called Fumizukitake), but it has never been developed into a commercial food crop. Its scientific value and its enzyme chemistry are the areas where it genuinely stands apart.
Interested in this species? Out-Grow carries a liquid culture.
Spring Fieldcap (Agrocybe praecox) Liquid CultureHow Is Spring Fieldcap (Agrocybe praecox) Classified?
| Rank | Name |
|---|---|
| Kingdom | Fungi |
| Phylum | Basidiomycota |
| Class | Agaricomycetes |
| Subclass | Agaricomycetidae |
| Order | Agaricales |
| Family | Strophariaceae |
| Genus | Agrocybe |
| Species | Agrocybe praecox (Pers.) Fayod |
| MycoBank ID | #356699 |
| NCBI Taxonomy ID | 71668 |
Naming History and Synonyms
Persoon's 1800 description as Agaricus praecox followed a convention of the era: nearly every gilled mushroom was initially assigned to the catch-all genus Agaricus, which has since been broken into hundreds of more precise genera. Independent botanists across Europe collected and named the same organism under different binomials — Agaricus togularis, Agaricus gibberosus, and several others — before its synonymy was resolved. The move to its own genus came in 1889 when Fayod not only created Agrocybe but designated A. praecox as its type species, giving the Spring Fieldcap permanent definitional authority over the entire genus.
| Synonym | Authority | Notes |
|---|---|---|
| Agaricus praecox | Pers., 1800 | Basionym — original description |
| Agaricus togularis | Bull. ex Pers., 1801 | Independent early description |
| Agaricus gibberosus | Fr., 1838 | Fries description, later sunk |
| Pholiota praecox | (Pers.) P. Kumm., 1871 | Transfer to Pholiota |
| Togaria praecox | (Pers.) W.G. Sm., 1908 | Short-lived genus Togaria |
| Agrocybe gibberosa | (Fr.) Fayod / Singer | Now sunk into A. praecox |
Family Placement — A Common Error in Older Guides
Many older British and European field guides assign Agrocybe praecox to the family Bolbitiaceae, following Rolf Singer's 1975 classification. Modern molecular phylogenetic analyses — including Matheny et al. (2006) and He et al. (2019) — place Agrocybe definitively within Strophariaceae. GBIF, Index Fungorum, and MushroomExpert.com all reflect the current placement. A 2013 multilocus study in PLOS ONE (Tóth et al.) independently confirmed that Agrocybe falls outside core Bolbitiaceae alongside Panaeolus. References to Bolbitiaceae in guides published before 2010 should be treated as outdated.
How Do You Identify Spring Fieldcap (Agrocybe praecox)?
The Species Complex — A Critical ID Caveat
In 1990, mycologists Flynn and Miller conducted mating compatibility experiments on Spring Fieldcap collections from across North America and Europe. Their finding was striking: what everyone called Agrocybe praecox was actually four morphologically indistinguishable biological species — organisms that look identical under any standard morphological examination but are reproductively isolated from one another. A fifth species, A. molesta (the Bearded Fieldcap), separates on habitat: it prefers open grassland rather than woodchip beds. Conventional spore measurements, gill counts, cap color, and even microscopic features cannot reliably separate these biological species. For practical purposes, any field identification of "Spring Fieldcap" from North American material should be understood as A. praecox sensu lato — the broader species complex — unless molecular or mating data are available.
Lookalike Species
⚠ Critical Safety Warning — Galerina marginata (Deadly Galerina)
Galerina marginata grows in exactly the same woodchip habitat as Spring Fieldcap, at the same season, with a similar brown-capped, ring-bearing appearance and brown spore print. It contains α-amanitin and γ-amanitin — the same amatoxins found in the Death Cap. Approximately 5 grams fresh weight has been estimated as potentially lethal for an adult. The poison causes delayed symptoms: gastrointestinal distress 6–24 hours after eating, followed by a deceptive remission, then acute liver failure 2–7 days later. Do not eat any ring-bearing brown mushroom from woodchip beds without a careful spore print and microscopic confirmation.
Galerina marginata — Deadly Galerina
Danger: Contains lethal amatoxins. Co-occurs in woodchip beds.
Key differences: Cap smaller (1.5–5 cm), ochre to rusty-orange (not pale tan). Spore print is rusty/ochre brown — not chestnut brown. Spores roughened/warted under microscope (vs. smooth in A. praecox). Stem often narrow (<6 mm), darkening toward near-black base.
Test: Take a spore print on white paper — rusty orange means danger.
Agrocybe molesta / A. dura — Bearded Fieldcap
Risk: Low — not toxic; part of the same species complex.
Key differences: Virtually identical macroscopically. Slightly larger spores (10–14 × 6.5–7.5 µm). Tends to favor open grassland over woodchip beds. Microscopy and habitat are the most useful separators.
Cyclocybe cylindracea — Poplar Fieldcap (Pioppino)
Risk: None — edible and popular.
Key differences: Typically larger with a more robust, persistent ring. Darker, more firmly brown cap. Found on or around poplar and willow wood, not mulch beds. The pioppino is a well-known cultivated mushroom.
Agrocybe acericola
Risk: Low — edibility unclear; not a target species.
Key differences: Darker yellow-brown cap. More persistent, better-developed ring. Prefers logs and buried wood rather than woodchip mulch.
Where Does Spring Fieldcap (Agrocybe praecox) Grow?
| Region | Range Notes | Season |
|---|---|---|
| UK & Ireland | Widespread; common in managed parks, roadside verges, wood-chipped borders | April–September, peak spring |
| Continental Europe | Northern, central, and southern Europe; documented in Germany, France, Netherlands, Scandinavia | Spring through early summer |
| Eastern North America | Illinois, Indiana, East Coast; moderately documented | Late spring, early summer; also fall in warm climates |
| Pacific Northwest | Documented in herbarium collections (Burke Herbarium) | Spring–early summer |
| Japan | Niigata and other temperate zones; known as Fumizukitake | Spring |
| Oceania | Also documented; range boundaries unclear | Austral spring |
Spring Fieldcap (Agrocybe praecox) is a consistent inhabitant of disturbed, nutrient-rich environments where lignocellulosic debris accumulates. Its primary urban habitat is woodchip and bark-chip mulch — the material spread beneath ornamental plantings in parks, garden borders, and streetscapes. It also colonizes compost-enriched soil, roadside verges with woody debris, and woodland edges where leaf litter and decaying wood intermingle. Notably, it thrives in greenhouse growing media with bark-based compost, which is how the specimens that led to the discovery of the agrocybyne compounds were first encountered — fruiting in a strawberry greenhouse in Niigata, Japan.
Because it prefers managed urban habitats that have increased globally in extent, the Spring Fieldcap is not a species under ecological pressure. The Burke Herbarium (Pacific Northwest) assesses it as "not of concern," and it does not appear on the IUCN Red List. Urbanization appears to benefit rather than threaten it.
Can You Cultivate Spring Fieldcap (Agrocybe praecox)?
Spring Fieldcap (Agrocybe praecox) is saprotrophic, which means it eats dead organic matter — not living roots or a living tree. That makes it cultivable in principle: unlike a mycorrhizal species such as a chanterelle or porcini, it needs no host to complete its life cycle. Published peer-reviewed work confirms that liquid culture of A. praecox is well-established in research settings. Fruiting under controlled conditions has not yet been standardized in any published protocol — but the biological groundwork exists, and the experimental path is reasonably clear.
What the Published Research Shows
The most detailed peer-reviewed cultivation data comes from a 2012 study by Fushimi et al. (Shizuoka University), which needed to produce large quantities of A. praecox mycelium to isolate the newly characterized agrocybyne compounds. Their liquid fermentation protocol used dextrose broth (Difco, 24 g/L) in a 30-liter jar fermenter, at 25°C with agitation (100 rpm) and aeration (1 L/min), over three weeks. The team processed 175 liters of culture broth to isolate enough material for structural analysis and bioactivity testing.
A second published line of culture work — from Steffen et al. (2002) in Enzyme and Microbial Technology — grew A. praecox in liquid culture specifically to purify manganese peroxidase (MnP), the lignin-degrading enzyme the species produces in quantity. MnP activity peaked at approximately 400 U/L in manganese-supplemented cultures. The same research group also confirmed successful colonization of straw substrate in solid-state culture, where A. praecox mineralized roughly 25% of radiolabeled synthetic lignin to CO₂ over 12 weeks — demonstrating real metabolic activity on a lignocellulosic substrate.
Why no published fruiting protocol? Three factors explain the gap: (1) there is no commercial incentive — the species is marginally edible and bitter; (2) the species complex identity issue means any protocol developed for one biological species may not replicate for another; and (3) research interest in A. praecox has centered on its enzyme system and secondary metabolite chemistry, not food production. The biology is not the limiting factor — the motivation has been.
The Experimental Cultivation Framework
Based on ecological data and the cultivation behavior of close relatives, the most plausible framework for experimental fruiting of Spring Fieldcap (Agrocybe praecox) involves pasteurized hardwood sawdust with a wheat bran supplement (analogous to the 8:2 ratio used for Cyclocybe aegerita, the Pioppino). Spring ecology suggests a fruiting trigger of a temperature drop to 12–16°C with high humidity above 85% RH — mimicking the cool-soil conditions of its natural spring emergence. These parameters are extrapolated from ecology and related species, not from published A. praecox-specific data, and should be treated as working hypotheses.
Inoculate from Liquid Culture
Use the Out-Grow liquid culture syringe to inoculate sterilized grain (rye, wheat, oat). Liquid culture provides pre-colonized mycelium for clean, fast spawn run.
Colonize Substrate
Transfer grain spawn to pasteurized hardwood sawdust + bran substrate (approx. 8:2 ratio by mass). Maintain 20–25°C. Full colonization expected in 2–4 weeks based on related species.
Initiate Fruiting
Drop temperature to 12–16°C (spring analogue). Maintain RH >85%. Introduce fresh air exchange. Spring Fieldcap ecology suggests a temperature differential as the primary fruiting trigger.
Research / Experimental Documentation
Document colonization rate, mycelium morphology, and any primordia (the first pin-stage structures). No validated biological efficiency data exists — contribute to what is known.
Liquid Culture Applications
For biochemistry or enzyme research: expand liquid culture as per the Fushimi protocol (25°C, agitation, 3 weeks). Supplement with Mn²⁺ for MnP production studies. Isolate agrocybyne metabolites from culture broth.
About the Out-Grow Spring Fieldcap Liquid Culture
The Out-Grow liquid culture for Spring Fieldcap (Agrocybe praecox) contains viable mycelium suspended in a nutritive medium, professionally prepared in a 12cc syringe for clean inoculation. Liquid culture is the validated research delivery format for this species — it is how both the Fushimi agrocybyne isolation and the Steffen/Hildén MnP characterization work were conducted.
For researchers: liquid culture provides the starting point for fermenter-scale production of agrocybyne compounds or MnP enzyme. For hobbyist cultivators: it provides a reliable foundation for experimental fruiting work on straw or hardwood sawdust substrate. For educators: it offers a fast-colonizing, spring-fruiting saprotroph well-suited to demonstrating fungal succession and decomposer ecology.
View Spring Fieldcap Liquid Culture →What Bioactive Compounds Does Spring Fieldcap (Agrocybe praecox) Contain?
Spring Fieldcap (Agrocybe praecox) has attracted genuine research interest for its secondary metabolite chemistry and enzyme production — these are not speculative attributes but characterized compounds with published structural data and measured bioactivity.
Agrocybynes A–E (Plant Growth Regulators from Culture Broth)
In a 2012 study in Phytochemistry, Fushimi et al. isolated five novel polyacetylenic amide compounds — named agrocybynes A through E — from the liquid culture broth of A. praecox strain F450. These are the first natural polyacetylene compounds of this structural class characterized from a mushroom. Agrocybyne B showed the most potent activity, inhibiting lettuce hypocotyl (seedling stem) growth by 70.4% at 1 micromole concentration. Agrocybyne D was notable as the first natural isolation of a compound previously known only from synthetic chemistry. The crystal structure of agrocybyne A was confirmed by X-ray crystallography (CCDC deposit 851177). Bioactivity in mammalian systems has not yet been tested — that gap is explicitly identified as a priority for future research.
Agrocybyne A
Octa-2,4-diynamide (C₈H₉NO). 29.6% hypocotyl inhibition at 1 µmol. Crystal structure confirmed by X-ray.
In vitro — plant bioassayAgrocybyne B
(E)-oct-4-en-2-ynamide (C₈H₁₁NO). Strongest plant-growth activity of the group: 70.4% hypocotyl inhibition at 1 µmol.
In vitro — plant bioassayAgrocybyne D
(E)-octa-6-en-2,4-diynamide (C₈H₇NO). First natural isolation of this compound — previously only synthetic.
In vitro — plant bioassayo-Orsellinaldehyde
From culture broth. IC₅₀ = 3.6 µg/mL (Hep 3B hepatoma cells). Known cytotoxic compound from Aspergillus research. DNA fragmentation suggests apoptosis mechanism.
In vitro — cell culture onlyManganese Peroxidase (MnP)
Extracellular enzyme; two isoforms (pI 6.3–7.0; MW ~42 kDa). Peak activity ~400 U/L in Mn²⁺-supplemented liquid culture. MnP1 isoform characterized as "atypical" by Hildén et al. 2014.
Biochemical characterizationFruiting Body Polysaccharides
Han et al. 2023: extraction rate 5.08% of dry mass. DPPH radical scavenging IC₅₀: 1.03 mg/mL. ABTS⁺ scavenging IC₅₀: 0.28 mg/mL.
In vitro — antioxidant assayPhenolic Compounds
Including ferulic acid, gallic acid, quercetin, and rutin (identified by LC-ESI-MS/MS in Iraqi study 2023). TPC: 49.7–52.7 mg GAE/g in water and ethanol extracts.
In vitro — antifungal / antioxidantAntifungal Activity
Ethanol extract inhibited seven Candida species and two Cryptococcus species in disc diffusion and broth dilution assays (Korkmaz & Bal 2023; Iraqi 2023 study).
In vitro — microbiology assayEvidence quality: All bioactivity results for Agrocybe praecox are currently in vitro only — conducted in laboratory cell cultures and biochemical assays. No animal model studies and no human clinical trials have been conducted. In vitro activity is hypothesis-generating, not clinically actionable, and these findings should not be interpreted as health claims.
Is Spring Fieldcap (Agrocybe praecox) Safe to Eat?
Spring Fieldcap (Agrocybe praecox) is generally classified as a marginally edible species — technically edible when well cooked, but not a recommended or enjoyable culinary mushroom for most people. The raw flesh is described as distinctly bitter, and at least one UK foraging authority describes it as "slightly poisonous raw," suggesting mild gastrointestinal risk from uncooked consumption. The bitterness diminishes but does not necessarily disappear with cooking. No specific toxin has been isolated from the species, and no documented cases of serious poisoning from correctly identified A. praecox appear in the literature reviewed.
The absence of documented poisonings does not mean the species is comprehensively safe. It is a minor, rarely consumed mushroom with limited safety data from large populations — "no known toxic cases" reflects limited consumption history, not a validated food safety record. Anyone choosing to eat it should cook it thoroughly and take a careful spore print first to exclude the co-occurring Galerina marginata.
A note on a dangerous mislabeling: At least one online vendor has labeled Agrocybe praecox as "hallucinogenic edible" with a "low to non-psychoactive potency level." This is factually false. Agrocybe praecox contains no documented hallucinogenic or psychoactive compounds. It is not related to psilocybin-containing species. Do not act on this mislabeling.
What Makes Spring Fieldcap (Agrocybe praecox) Remarkable?
Spring's Earliest Gilled Mushroom
The epithet praecox — Latin for "early" or "precocious" — was earned. Spring Fieldcap (Agrocybe praecox) consistently appears among the first gilled mushrooms to fruit each year, emerging as soon as soil temperatures become sufficient in spring. This is not merely a phenological curiosity: it implies specific adaptation to low-temperature substrate colonization and fruiting triggers that differ from summer and autumn species. For cultivators interested in temperature-driven fruiting biology, it is a genuinely instructive study subject.
The Species Complex Paradox
Flynn and Miller's 1990 mating study revealed a remarkable biological situation: four completely distinct, reproductively isolated biological species — confirmed as separate by mating incompatibility — that no standard morphological examination can distinguish. Identical cap color, spore measurements, gill density, and microscopic anatomy conceal the genetic boundaries. This kind of morphological stasis with reproductive divergence is relatively rare in fungi. Whether these biological species are in the process of speciating (recent divergence) or under stabilizing selection that preserves morphology despite genetic separation remains an open question. A modern multilocus molecular phylogeny of the complex has not been published.
The Strawberry Mystery
In 2007, A. praecox appeared in a Niigata, Japan greenhouse where nearby strawberry plants were displaying abnormal fruit enlargement. An earlier 1980 Japanese report had documented an Agrocybe species causing the opposite effect — strawberry fruit shrinkage. These opposing effects from the same or closely related fungus prompted Fushimi et al. to investigate the chemistry, leading to the discovery of the agrocybynes as diffusible plant-growth regulators. How a saprotrophic wood-decomposer interacts chemically with living crop plants via secreted compounds is not yet understood — it is a genuinely novel research dimension with no published explanation.
An Atypical Manganese Peroxidase
Manganese peroxidase (MnP) is the primary enzyme class that allows white-rot and litter-decomposing fungi to break down lignin — the tough, aromatic polymer that makes wood resistant to decay. Agrocybe praecox produces MnP in high quantity in liquid culture, and its MnP1 isoform was characterized by Hildén et al. (2014) in Fungal Genetics and Biology as "atypical" — structurally or functionally deviating from canonical MnP biochemistry in ways that make it a reference point in comparative fungal peroxidase research. This is an organism that has earned a place in the industrial enzyme literature on its own terms.
Genome in the 1000 Fungal Genomes Project
The U.S. Department of Energy's Joint Genome Institute (JGI) sequenced the A. praecox strain OKM6292 genome as part of the 1000 Fungal Genomes initiative, an international effort to build a comprehensive genomic reference library for fungal diversity. The annotated draft assembly is available through JGI MycoCosm. This genome provides the raw material for comparative PCWD (plant cell wall-degrading) enzyme analysis, biosynthetic gene cluster identification for the agrocybyne pathway, and phylogenomic reconstruction — most of which remains unpublished work waiting for researchers.
PAH Bioremediation Potential
In a soil-straw experimental system, A. praecox mineralized 4–6% of radiolabeled benzo[a]pyrene — a Class 1 human carcinogen — over 12 weeks. While this rate is lower than Stropharia rugosoannulata, the most efficient PAH (polycyclic aromatic hydrocarbon) degrader in the same study, A. praecox has a practical advantage: it colonizes urban woodchip beds naturally and prolifically. A decomposer already present in contaminated urban green spaces — one capable of mineralizing carcinogenic soil pollutants — represents a bioremediation asset that does not require deliberate large-scale inoculation.
Within a screening of 27 litter-decomposing basidiomycetes by Steffen et al. (2000), Spring Fieldcap (Agrocybe praecox) ranked among the most enzymatically active species, alongside Stropharia coronilla and S. rugosoannulata — fungi that have attracted considerable research interest in their own right. The Spring Fieldcap's place on that list is not incidental.
Also available as a culture plate from Out-Grow.
Spring Fieldcap (Agrocybe praecox) Culture PlateFrequently Asked Questions About Spring Fieldcap (Agrocybe praecox)
Is Spring Fieldcap (Agrocybe praecox) edible?
Technically yes, but it is classified as a marginal edible. The raw flesh is bitter and potentially mildly irritating — at least one UK foraging authority describes it as "slightly poisonous raw." Cooked, the bitterness diminishes but may not fully disappear. It is not a choice edible, and foraging for it carries meaningful risk of mistaking it for the deadly Galerina marginata, which grows in the same woodchip habitat. A spore print on white paper is an essential step: Spring Fieldcap leaves a medium chestnut-brown print; Galerina marginata leaves a rusty/ochre print.
How do I tell Spring Fieldcap apart from Galerina marginata?
The most reliable field-accessible test is the spore print: place the cap gill-side-down on white paper for at least an hour. Spring Fieldcap leaves a medium to dark chestnut-brown print. Galerina marginata leaves a rusty, ochre-brown print — distinctly more orange. Under a microscope, the difference is definitive: A. praecox spores are smooth and thick-walled; G. marginata spores are roughened or warted. Cap size is also a rough guide — Galerina caps are typically smaller (1.5–5 cm). When in doubt, do not eat it.
Can Spring Fieldcap (Agrocybe praecox) be cultivated at home?
It is saprotrophic and in principle cultivable on dead lignocellulosic substrate — no living host is required. Liquid culture and straw colonization have been confirmed in peer-reviewed research settings. A reliable fruiting protocol for home or laboratory settings has not been published. The most plausible experimental approach uses pasteurized hardwood sawdust with wheat bran, a temperature drop to 12–16°C to mimic spring conditions, and high humidity above 85%. The Out-Grow liquid culture provides a research-ready starting point for this work.
What are the agrocybynes, and why do they matter?
Agrocybynes A–E are novel polyacetylenic amide compounds first isolated from Agrocybe praecox culture broth by Fushimi et al. in 2012. They are plant-growth regulators — compounds that inhibit seedling stem and root growth at micromolar concentrations. Agrocybyne D was the first natural isolation of a compound previously only known from synthetic chemistry. Their bioactivity in mammalian systems has not been tested yet. The discovery came after A. praecox appeared in a Japanese strawberry greenhouse where fruits were abnormally enlarged — the agrocybynes were part of the scientific investigation into that interaction.
Is Spring Fieldcap psychoactive or hallucinogenic?
No. Agrocybe praecox contains no documented psychoactive or hallucinogenic compounds. It is not related to psilocybin-producing species. At least one online vendor has incorrectly labeled it as hallucinogenic — this claim has no scientific basis and should be disregarded entirely. The species is a wood-decomposing saprotroph with documented polyacetylene and phenolic chemistry; none of those compounds has any documented psychoactive mechanism.
What is the Agrocybe praecox species complex?
Research by Flynn and Miller (1990) demonstrated through mating compatibility experiments that what mycologists call "Agrocybe praecox" is actually four reproductively isolated biological species that cannot be distinguished by any standard morphological character — spore measurements, cap color, gill density, or microscopy. A fifth related species, A. molesta, is separated primarily by habitat (grassland vs. woodchip). For practical identification purposes, a Spring Fieldcap from North American material should be understood as belonging to the A. praecox sensu lato complex unless molecular data are available.