''Agaricus abramsii'' is a species of

mushroom A mushroom or toadstool is the fleshy, spore-bearing Sporocarp (fungi), fruiting body of a fungus, typically produced above ground on soil or another food source. ''Toadstool'' generally refers to a poisonous mushroom. The standard for the n ...

-forming

fungus A fungus (: fungi , , , or ; or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and mold (fungus), molds, as well as the more familiar mushrooms. These organisms are classified as one ...

in the family

Agaricaceae The Agaricaceae are a family of basidiomycete fungi and include the genus ''Agaricus'', as well as basidiomycetes previously classified in the families Tulostomataceae, Lepiotaceae, and Lycoperdaceae. Taxonomy The family Agaricaceae was publishe ...

. It is

endemic Endemism is the state of a species being found only in a single defined geographic location, such as an island, state, nation, country or other defined zone; organisms that are indigenous to a place are not endemic to it if they are also foun ...

to the Santa Cruz Mountains of

California, USA California () is a state in the Western United States that lies on the Pacific Coast. It borders Oregon to the north, Nevada and Arizona to the east, and shares an international border with the Mexican state of Baja California to the sout ...

. It was first described described by mycologist William A. Murrill in 1912. It is notable for its irregular, thick, and fleshy cap.

Description

The pileus (cap) of ''Agaricus abramsii'' is irregular in shape due to the position of the plant, measuring approximately 6 cm in

diameter In geometry, a diameter of a circle is any straight line segment that passes through the centre of the circle and whose endpoints lie on the circle. It can also be defined as the longest Chord (geometry), chord of the circle. Both definitions a ...

. The surface is dry, finely

imbricate Aestivation or estivation is the positional arrangement of the parts of a flower within a flower bud before it has opened. Aestivation is also sometimes referred to as praefoliation or prefoliation, but these terms may also mean vernation: the ar ...

-scaly, and whitish with a rosy tint. The

lamellae Lamella (: lamellae) means a small plate or flake in Latin, and in English may refer to: Biology * Lamella (mycology), a papery rib beneath a mushroom cap * Lamella (botany) * Lamella (surface anatomy), a plate-like structure in an animal * Lame ...

(gills) are free, crowded, narrow, and plane, with a pallid coloration.

Spores In biology, a spore is a unit of sexual (in fungi) or asexual reproduction that may be adapted for dispersal and for survival, often for extended periods of time, in unfavourable conditions. Spores form part of the life cycles of many plant ...

are

ovoid An oval () is a closed curve in a plane which resembles the outline of an egg. The term is not very specific, but in some areas of mathematics (projective geometry, technical drawing, etc.), it is given a more precise definition, which may inc ...

, smooth, and range from

hyaline A hyaline substance is one with a glassy appearance. The word is derived from , and . Histopathology Hyaline cartilage is named after its glassy appearance on fresh gross pathology. On light microscopy of H&E stained slides, the extracellula ...

to pale umbrinous under a microscope, measuring 6–7 × 3.5–4 μm. The stipe (stem) is eccentric and fusiform, white, polished, and hollow, measuring approximately 6 cm in length and 2 cm in thickness. The annulus is located near the base, white, and not conspicuous.

Habitat

''Agaricus abramsii'' was discovered growing on a clay bank by the roadside at an elevation of 800 feet in the

Santa Cruz Mountains The Santa Cruz Mountains ( Mutsun Ohlone: Mak-sah-re-jah, "Sharp Ridged Mountain of the Eagle" or "People of the Eagle Mountain") are a mountain range in central and Northern California, United States, constituting a part of the Pacific Coast R ...

near

Palo Alto, California Palo Alto ( ; Spanish language, Spanish for ) is a charter city in northwestern Santa Clara County, California, United States, in the San Francisco Bay Area, named after a Sequoia sempervirens, coastal redwood tree known as El Palo Alto. Th ...

. The type specimen was collected by W. A. Murrill and L. R. Abrams on November 25, 1911. The irregular shape of the pileus is attributed to its position on the side of the bank.

References

abramsii Taxa named by William Alphonso Murrill Fungi described in 1912 Fungus species {{Fungi-stub