Reviewed by Elena Ramirez, Mold Remediation & Drying Specialist, IICRC AMRT #327506, October 2026.
Short answer: The mold species that show up most often in Utah homes are Cladosporium, Aspergillus, Penicillium, Alternaria, Stachybotrys chartarum, and Chaetomium. Visual identification cannot reliably distinguish them — what looks like “black mold” could be any of several species. A lab test is the only way to confirm. The good news: the remediation process under the IICRC S520 standard is similar regardless of species, so remediation can start without a lab result in hand.
Why six species, and why these six
There are tens of thousands of mold species in the world, but only a few dozen grow indoors with any regularity, and six of those account for the vast majority of what we see in Spanish Fork, Mapleton, Payson, Salem, Saratoga Springs and Springville. These are the species that thrive on common building materials (drywall paper, cellulose insulation, wood, carpet backing), tolerate the humidity swings of a Utah home, and spore readily enough to show up on a visual inspection.
None of what follows is medical advice. Specific health questions belong with your doctor — especially if anyone in your household has asthma, mold allergies, or a compromised immune system. These descriptions are meant to help you recognize what you may be looking at, understand why identification matters less than most people think, and know when to call for a professional inspection.
The six species we see most in Spanish Fork and Utah County
1. Cladosporium
Cladosporium is probably the mold you have seen the most without realizing it. It grows on painted surfaces, especially around windows where condensation forms, in bathrooms on grout and caulk, inside damp HVAC drip pans, and on fabrics in basements. It thrives in both warm and cool conditions, which is why we find it year-round in Utah homes. Spots are usually small, dark, and slightly raised. Under a microscope the spore chains look like dark branching trees. In a home it looks like black speckling spreading outward from a seed point. Cladosporium is often the first mold a homeowner notices, because it tolerates the lower humidity that other species need more of.
2. Aspergillus
Aspergillus is a huge genus with dozens of species that look very different from each other. Aspergillus niger is black and often mistaken for Stachybotrys. Aspergillus flavus is yellow-green. Aspergillus fumigatus is grey-green. In Utah homes, Aspergillus commonly grows on walls after a water loss, in insulation that got wet and was not dried properly, in attic dust, and in HVAC systems. It is one of the few species where identification matters at a clinical level — some Aspergillus species produce mycotoxins and some do not — but the remediation process is the same.
3. Penicillium
Penicillium is the mold most strongly associated with post-water-damage growth. Within 48 to 72 hours of unaddressed water, Penicillium can colonize carpet pad, wet drywall, and the paper backing of insulation. It looks blue-green or grey-green, often with a powdery texture. The genus includes the species that gives us penicillin (Penicillium notatum) and the species that produces blue cheese veining, but the indoor-mold species we deal with are not the medicinal or culinary ones. If you had a leak this week and now see blue-green dots on drywall, it is almost certainly Penicillium.
4. Alternaria
Alternaria shows up in showers, around tubs, under sinks, around windows that condense, and on damp basement walls. It is dark green to brown and often has a slightly velvety texture. Alternaria produces a lot of airborne spores and is one of the most common outdoor molds, which means spores enter homes through doors, windows, and HVAC intakes constantly. It only grows indoors where there is moisture to feed it. Common Alternaria growth sites: the top of the inside of a toilet tank, the silicone seal around a tub, the window track under a slider.
5. Stachybotrys chartarum (“black mold”)
Stachybotrys chartarum is the species people mean when they say “black mold” or “toxic mold.” The term “toxic mold” is a popular shorthand — molds themselves are not toxic, but some species including Stachybotrys produce mycotoxins under certain conditions. Stachybotrys needs sustained moisture over days to weeks to grow — it does not colonize a surface that dries out between wettings. It is slimy or dark greenish-black when wet, and dry chalky black when old. It grows on cellulose-based materials: paper-faced drywall, cardboard, fiberboard, cellulose insulation. In Utah homes we see it where water sat for a week or more before anyone noticed — a slow pinhole leak behind a wall, a flooded basement that was not fully dried, a crawlspace with chronic groundwater. Visual identification alone cannot confirm Stachybotrys; a lab test is required.
6. Chaetomium
Chaetomium is a cottony mold that starts white, turns grey, and darkens to black as it ages. It has a distinctive musty, earthy smell — often described as the strong “basement smell.” Chaetomium grows on wet drywall after plumbing leaks, roof leaks, and chronically damp basements. Along with Stachybotrys, Chaetomium is one of the molds that indicates sustained moisture, so finding it is usually a sign of a water source that has been active for a while. Removal of the colonized material is required — cleaning Chaetomium off wet drywall does not work.
Which species we usually find where
This is a general pattern, not a rule. Any species can grow anywhere given moisture and food:
| Location | Most common species |
|---|---|
| Bathroom (grout, caulk, shower) | Cladosporium, Alternaria |
| Around windows that condense | Cladosporium, Alternaria |
| Attic sheathing (vent problem) | Cladosporium, Aspergillus |
| Basement walls (cold concrete) | Cladosporium, Alternaria, Chaetomium |
| Drywall after a recent water loss (less than a week) | Penicillium |
| Drywall after a prolonged leak (over a week) | Stachybotrys, Chaetomium |
| HVAC drip pan or ductwork | Cladosporium, Aspergillus, Penicillium |
| Crawlspace | Aspergillus, Chaetomium, Stachybotrys |
| Water-damaged carpet pad | Penicillium, Aspergillus |
| Wood framing (chronic moisture) | Chaetomium, Stachybotrys |
Why identification matters less than most people think
The IICRC S520 standard — the industry rulebook for professional mold remediation — treats all visible mold as something to remove, regardless of species. Containment with plastic sheeting and negative air pressure, removal of contaminated porous materials, HEPA air scrubbing, and antimicrobial treatment on remaining surfaces are the same whether the species is Cladosporium or Stachybotrys. Nothing about the remediation changes based on a lab result.
Species identification matters when:
- Legal documentation. Landlord-tenant disputes, real estate disclosures, insurance disputes, or liability cases where a specific species needs to be named on paper.
- Medical concerns. If a doctor needs the species to make treatment decisions for a patient with mold allergy, aspergillosis, or an immune condition.
- Insurance borderline cases. Where the carrier might deny coverage based on species, or where confirming Stachybotrys might trigger a different sublimit.
- Post-remediation clearance. After the work is done, independent air sampling confirms spore counts have returned to normal background levels.
For those situations, our $349 inspection includes air sampling with lab analysis, so you get documented results rather than a visual opinion. If a dispute calls for a consultant with no role in any remediation, you are free to hire one, and we will work from their findings.
What to do if you see any of these in your home
- Do not disturb it. Do not brush, wipe, bleach-spray or vacuum it. Those actions release spores into the air and spread the contamination.
- Find and stop the moisture source. Mold cannot grow without water. A plumbing leak, roof leak, condensation problem, or humidity issue is behind every colony.
- Close off the affected room. Keep interior doors closed to limit spore movement. If HVAC is involved, consider shutting off the system.
- Book a mold inspection. Our IICRC AMRT-certified technicians inspect visually, map the moisture, and give you a written scope and quote. If you need lab testing, our $349 inspection includes air sampling with lab analysis.
- Keep vulnerable people out. Children, elderly, pregnant, immunocompromised, asthmatic, and mold-allergic household members should stay out of the affected area until remediation is complete.
Related reading
- Is that dark spot mold or dirt? 5 ways to tell
- Mold remediation vs mold removal: what’s the difference?
- Mold cleanup: when DIY is fine and when to call a pro
- Black mold removal in Spanish Fork, UT
- Mold inspection and testing in Spanish Fork
Call (385) 247-9387. Mold inspections from $99 by IICRC AMRT-certified technicians Marcus Holloway (#263814) and Elena Ramirez (#327506). Free remediation estimate. 24/7 live-answered line.