Calvatia booniana, commonly known as the Western Giant Puffball, is an extraordinary mushroom species belonging to the Puffball family that grows predominantly in the Rocky Mountains of western North America. This remarkable mushroom species possesses several distinctive attributes such as an astonishingly large fruiting body growing up to 60 cm in diameter, a sculpted cap surface that resembles a tortoise shell, and an exceptional ability to produce a massive amount of spores.
C. booniana was initially identified and classified as a unique species in 1964 by Dr. Alexander H. Smith, a celebrated mycologist from the University of Michigan. Smith gave the newly identified species its epithet in honor of William Judson Boone, an esteemed botanist and the inaugural president of the College of Idaho. [i]
Identification and Description[ii] [iii] [iv]
The identification of this species is very easy based on its striking outward appearance.
Fruiting Body: Calvatia booniana is predominantly characterized by a rounded or lobed spore case, which is typically flattened or depressed at the top and firmly attached to its substrate through root-like rhizomorphs. The fruiting body of this species exhibits exceptional size, with widths ranging from 15 to 60 cm or even larger, and heights ranging from 7 to 30 cm or more. The outer skin layer, known as the (exo)peridium, envelops the internal contents of the fruiting body and possesses significant thickness, measuring up to 0.5 mm. The surface peridium of young fruiting bodies appears smooth or tomentous, and has at first a whitish coloration, that later transitions to a grayish-white or grayish-tan color. As the mushroom matures, it develops large, raised, and irregularly shaped warts with brownish centers. Over time, these warts either separate to form flattened scales or plates that will fall away to reveal a pale grayish, glabrous to felty endoperidium, or dehisce to reveal an underlying solid spore-bearing mass (gleba).
Flesh: The flesh of Calvatia booniana is comprised by a spore-bearing mass, called a gleba. Initially, the spore-bearing mass is white, but it soon transitions to yellowish-green, olive-brown, and finally brown, as it progresses through the aging process. Eventually, the spore mass becomes powdery, at which time the mature spores may be released.
Stem: C. booniana does not possess a distinct stem or basal stem-like region. Instead, the fruiting bodies of this species are directly connected to the underlying ground substrate through basal cords known as rhizomorphs. These small cords serve as the anchor, firmly attaching the fruiting bodies to their substrate.
Spores: The spores of C. booniana measure 3.5-5.5 µm in diameter. They are round or nearly round, smooth or minutely spiny. The capillitilia, which are filamentous threads that retain spores, are septate, wavy, and thick-walled with round pits, narrowed at tips, measuring 2-9 µm in diameter.
Spore Print: Spore prints of this species are olive-brown to brown in deposit.
Smell: C. booniana does not typically have a distinctive odor, however, very old specimens may develop an unpleasant smell.
Edibility: This mushroom specie is considered edible, but only when its “flesh” is still firm and white. When the internal flesh begins to exhibit any change in color, such as yellow, olive, brown, or similar colors, it is no longer suitable for consumption. It is essential to thoroughly check all specimens for the presence of maggots or any signs of infestation before consumption.
Habitat and Ecology: C. booniana can be found growing solitarily, scattered, or in gregarious clusters in grassy fields or beneath sagebrush within arid or semi-arid regions of western North America. In addition the growth pattern mention, this species is also known for its ability to form fairy rings
Range: This species is known to grow in states located west of the Rockies, encompassing regions such as Colorado, Idaho, Montana, Nevada, New Mexico, and the mountainous areas of Southern California.
Fruiting season: The fruiting season of the Western Giant Puffball Mushroom, Calvatia booniana, exhibits variations depending on its geographical location. In the coastal zones of western North America, this species is known to fruit from mid-winter to spring. On the western slopes of the Sierra Nevada, the fruiting season typically occurs in late spring. Conversely, in the Eastern Sierra Nevada, giant puffball mushroom tends to fruit during the summer months.
Look-A-Likes [v]
While Calvatia booniana is a unique and distinctive mushroom species, there are a few look-alike species that may resemble it in certain aspects. The following are a few species that may resemble Calvatia booniana:
- Calvatia gigantea – this species serves as the eastern counterpart of Calvatia booniana, but it may also be found in the western regions, particularly during wet years. Its most notable distinguishing characteristic is the smooth and relatively featureless cap surface, which starkly contrasts with the sculpted and tortoise shell-like cap of Calvatia booniana.
- Calvatia polygonia – this is a similar species found in western regions. It can be differentiated from C. booniana by its prominently ornamented spores and generally smaller dimensions, typically ranging from 5 to 16 cm in diameter.
- Calbovista subsculpta – this species can be distinguished from C. booniana by its smaller size, typically ranging from 10 to 15 cm in diameters; an (exo)peridium that features broader and less prominent pyramidal warts; a well-developed base below the gleba called the subgleba; and a distinctive capillitium composed of individual elements with short antler-like side branches.
- Calvatia sculpta – this species is also smaller than C. Booniana, typically growing from 5 to 20 cm in diameter. Additionally, C. sculpta has large, hooked warts and a usually well developed pseudostipe.
- Calvatia pachyderma – this species can be differentiated from C. booniana by a nearly smooth exoperidium and fruiting body that tends to open by large vertical splits.
Toxicity and Safety[vi]
Calvatia booniana is generally considered to be non-toxic and edible when it is young and its flesh is firm and white. However, it is important to exercise caution when consuming any wild mushroom, as there is always a risk of misidentification and potential toxicity.
Furthermore, it is important to note that some individuals may have individual sensitivities that can result in gastrointestinal discomfort and disturbances when consuming Calvatia booniana. These effects can include a mild laxative effect due to the mushroom’s potential to mildly stimulate the digestive system, potentially causing increased bowel movements or loose stools.
References:
[i] McKnight, K. H., McKnight, V. B., & Peterson, R. T. (1998). Giant Puffball A Field Guide to Mushrooms: North America (Peterson Field Guides) Houghton Mifflin
[ii] Kuo, M. (2017, December). Calvatia booniana.
[iii] D. Arora (1986) Calvatia booniana (Western Giant Puffball) In “Mushrooms Demystified: A Comprehensive Guide to the Fleshy Fungi,” Ten Speed Press, Berkeley (pp. 682)
[iv] Wood, M. (2010). California Fungi – Calvatia booniana.
[v] Lincoff, G. (1981). Western Giant Puffball. In National Audubon Society Field Guide to North American mushrooms (pp. 821–822). Knopf.
[vi] Richter, D.L., & Morse, B.L. (2008). The Western Giant Puffball (Calvatia Booniana A. H. Smith) In Northern Michigan. The Michigan Botanist, 47.
