Morchella frustrata is a later synonym of Morchella tridentina, a species originally described by Giacomo Bresadola from north Italy in 1898. It is a species of fungus in the family Morchellaceae referred to as the mountain blond or western blond morel in North America, but commonly found throughout the Mediterranean basin. It has conical, grey to buff fruit bodies that grow up to 20 cm (7.9 in) tall and 5 cm (2.0 in) wide. Recent molecular and morphological studies have also shown Morchella frustrata to be conspecific to M. quercus-ilicis, M. elatoides, M. elatoides var. elegans and M. conica var. pseudoeximia (Richard et al. 2014, Loizides et al. 2015). So far, this cosmopolitan species is known from California and Oregon in North America, from Argentina and Chile in South America, from Spain, France, Cyprus, Italy and Turkey in Europe, and has also been reported from Israel and India.
Morchella frustrata was described as new to science in a 2012 publication by Michael Kuo and colleagues. The report resulted from the Morel Data Collection Project, which aimed to clarify aspects of the biology, taxonomy and distribution of North American Morchella, and described 14 new morel species. The type locality was in Placer County, California. The morel was previously referred to as phylogenetic species (i.e., defined by DNA sequence rather than morphological characteristics) Mel-2 in a study the year before, and informally as the "mountain blond morel". Despite its light color, M. frustrata belongs to the Elata clade along with other black morels, including M. tomentosa and M. angusticeps. The specific epithet frustrata refers to the "frustrating combination of black and yellow morel features that characterize the species."
In two subsequent studies, however, Richard et al. (2014) and Loizides et al. (2015) used DNA analysis to determine that this species is identical to morels collected in southern Europe, matching the original description of Morchella tridentina by Bresadola. This name therefore takes precedence over M. frustrata.
The fruit bodies are often rufescent and 9–20 cm (3.5–7.9 in) high. The conical cap is 4–6 cm (1.6–2.4 in) high and 2.5–4 cm (1.0–1.6 in) wide at the widest point. The cap surface features pits and ridges, which are formed from the intersection of 16–22 primary vertical ridges and few shorter, secondary vertical ridges, with frequent, sunken, horizontal ridges. The cap is attached to the stipe with a distinct sinus about 2–4 mm deep and 2–4 mm wide. The smooth, splitting ridges remain persistently pale throughout the maturity process, easily distinguishing this species from other species in section Elata, or black morels, which have ridges that typically darken with age. Pits are usually elongated vertically. They are smooth, dull grayish to pale yellowish or nearly whitish when young, later becoming pale tan to pale pinkish tan. The stipe is 2–6 cm (0.8–2.4 in) high by 1–4 cm (0.4–1.6 in) wide and is more or less equal in width throughout its length or sometimes thicker at the base. Its whitish surface is smooth or finely mealy with whitish granules. The flesh is whitish and measures 1–2 mm thick in the hollow cap. The sterile inner surface of the cap is whitish and pubescent (having soft, short and erect "hairs").
The ascospores are smooth, elliptical, and measure 20–26 by 13–18 µm. Asci (spore-bearing cells) are cylindrical, eight-spored, hyaline (translucent) when mounted in dilute (2%) potassium hydroxide (KOH), and measure 225–330 by 15–25 µm. Paraphyses are cylindrical to capitate or moniliform, measuring 95–250 long by 10–25 µm wide, and are septate. Their tips are rounded to somewhat club-shaped or infrequently somewhat fuse-shaped. Elements on the sterile ridges are 50–175 by 12.5–20 µm, and septate. The terminal cells are club-shaped or nearly so.
Although the edibility of M. frustrata was not mentioned in the original description, Kuo has elsewhere written of the edibility of North American Morchella. In general, morels should not be eaten raw, as they can trigger allergic reactions in susceptible individuals. Their flavor is enhanced after they are fried, stuffed, or dried.
This species is very similar to Morchella rufobrunnea, another rufescent, cosmopolitan species with pale colours, which is nonetheless found in urban and suburban areas. The latter is distinguished by an adnate cap lacking a sinus and a distinct dark pruinescence on the stem, more pronounced in young fruit bodies. Due to its similar light coloration, M. frustrata may also be confused with Morchella esculentoides; as Kuo states, "it looks like a black morel with the colors of a yellow morel." The vertically arranged pits and ridges, as well as the slight indentation where the cap meets the stem on M. frustrata, however, more closely resemble the black morels such as M. elata. M. snyderi is somewhat similar in appearance to young specimens of M. frustrata, but mature specimens of the former species can be distinguished by the brown to black ridges on the cap, and the ridged and pocketed stipe.
Habitat and distribution
Morchella frustrata fruit bodies grow solitary, scattered, or in small groups in spring, in mountainous forests and maquis. The exact ecological preferences of the fungus are not yet known with certainty, but it is suspected to be fucaltitive mycorrhizal or biotrophic. Tree species associated with the fungus include pacific madrone (Arbutus menziesii), oaks (Quercus spp.), Douglas fir (Pseudotsuga menziesii), ponderosa pine (Pinus ponderosa), sugar pine (Pinus lambertiana), and white fir (Abies concolor).  In Europe it is often found with holm oak (Quercus ilex), strawberry trees (Arbutus andrachne), olive trees (Olea europaea), Spanish fir (Abies pinsapo), Silver fir (Abies alba) and Scot's pine (Pinus sylvestris). Although it was originally hypothesized that collections of M. frustrata from Turkey might have been recently introduced from North America, numerous collections reported since from remote and undisturbed areas in the Mediterranean and the Alps (including Bresadola's original collection from Trentino), suggest a long-time and well-established presence of this species in Europe.  Kuo suggests that it might be also widely distributed in western North America, but so far has only been confirmed to be present in Oregon and California.
- Kuo M. "The Morchellaceae: True Morels and Verpas". MushroomExpert.com. Retrieved 2013-12-16.
- Kuo M, Dewsbury DR, O'Donnell K, Carter MC, Rehner SA, Moore JD, Moncalvo J-M, Canfield SA, Stephenson SL, Methven AS, Volk TJ. (2012). "Taxonomic revision of true morels (Morchella) in Canada and the United States". Mycologia 104 (5): 1159–77. doi:10.3852/11-375. PMID 22495449.
- O’Donnell K, Rooney AP, Mills GL, Kuo M, Weber NS, Rehner SA. (2011). "Phylogeny and historical biogeography of true morels (Morchella) reveals an early Cretaceous origin and high continental endemism and provincialism in the Holarctic". Fungal Genetics and Biology 48 (3): 252–65. doi:10.1016/j.fgb.2010.09.006. PMID 20888422.
- Pilz D, McLain R, Alexander S, Villarreal-Ruiz L, Berch S, Wurtz TL, Parks CG, McFarlane E, Baker B, Molina R, Smith JE. (March 2007). Ecology and management of morels harvested from the forests of western North America. General Technical Report PNW-GTR-710. Portland, Oregon: U.S. Forest Service Pacific Northwest Research Station.
- Richard, Franck; Bellanger, Jean-Michel; Clowez, Philippe; Courtecuisse, Regis; Hansen, Karen; O'Donnell, Kerry; Sauve, Mathieu; Urban, Alexander; Moreau, Pierre-Arthur (30 December 2014). "True morels (Morchella, Pezizales) of Europe and North America: evolutionary relationships inferred from multilocus data and a unified taxonomy". Mycologia (Preliminary version published online). doi:10.3852/14-166. PMID 25550303. 14-166.
- Kuo M. (2005). Morels. Ann Arbor, Michigan: University of Michigan Press. p. 173. ISBN 978-0-472-03036-1.
- Kuo M. (November 2012). "Morchella frustrata". MushroomExpert.com. Retrieved 2013-12-15.
- Taşkın H, Büyükalaca S, Hansen K, O’Donnell K. (2012). "Multilocus phylogenetics analysis of true morels (Morchella) reveals high levels of endemics in Turkey relative to other regions of Europe". Mycologia 104 (2): 446–61. doi:10.3852/11-180. PMID 22123659.
- Loizides, Michael; Alvarado, Pablo; Clowez, Philippe; Moreau, Pierre-Arhtur; de la Osa, Luis Romero; Palazón, Antonio (14 March 2015). "Morchella tridentina, M. rufobrunnea, and M. kakiicolor: a study of three poorly known Mediterranean morels, with nomenclatural updates in section Distantes". Mycol Progress (published online). doi:10.1007/s11557-015-1030-6. 14:13.
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