The species is distinguished by a rimose pileus, a margin that is initially fimbriate and apendiculate, a narrow stipe that is concentrically squamulose to rimulose-squamulose, up to farinose, but no forming bands. It was compared to Macrolepiota procera by Singer (1951) [1949] but the latter species is not found in Argentina.

Description are available from Singer (1951) [1949] and Spegazzini (1880).

An outstanding agaric in the Lepiotoid fungi with a saprophyte habitat. Reported only on grassy habitats in Central East Argentina, around the Buenos Aires area. Based on recent collections compared to previous herbarium records its population is diminishing due to habitat loss..

Criteria:
C2ai EN: based on the poor number of species found
D1 EN: based on the number of mature individuals found

Only known from two localities in spite of persistent search:
Macrolepiota bonaerensis was described from Buenos Aires province near Buenos Aires city and afterwards recorded only from Parque Nacional El Palmar, Entre Rios (31°51′11″ S, 58°19′21″ W) (see map)

Based on recent collections compared to previous herbarium records its population is diminishing. Ongoing studies show that M. bonaerensis herbarium materials spanned along years 1888-2008 sum up 21 specimens among Lepiotaceous fungi (246 collections of Lepiotaceous fungi, 39 of Macrolepiota, 21 of M. bonaerensis). A specific ongoing research on Lepiotaceous fungi from Argentina (geographic region) carried along 5 years has only recovered 2 specimens of M. bonaerensis out of 27 Macrolepiota specimens recovered from 200 new collection in these 5 years period.
A poorer finding of the species in spite of a special focusing on Lepiotaceous indicates a diminishing trend of this taxon; mainly when one considers that findings in the 120 years period did not specially focused on M. bonaerensis.

A grassland species but apparently rejecting human labored lands.

Solitary and eventually gregarious. Saprotrophic and terrestrial in open places, always outside woodland, in grasslands, and along roadsides.

Habitat loss.
Slow mycelial growth and weakness (difficult to keep them after replication).

Need of ecological studies in order to set the species requirements.

A manuscript entitled The genus Macrolepiota in Argentina is being elaborated that shows molecular based support of the species.
The species needs a deeper ecological characterization .
Knowledge on specific requirements for fruiting is needed in order to understand the diminishing trend of its population.

Singer, R.; Digilio, A.P.L. (1952). Prodromo de la flora agaricina Argentina. Lilloa, Revista de Botánica 25: 5-461.
Spegazzini, C.L. (1880). Fungi Argentini. Pugillus 2. Anales de la Sociedad Científica Argentina 9 (6):  278.