Symphyotrichum potosinum

The leaves are thin and grass-like, hairless or nearly so. Those at the base have long, sheathing, sparsely ciliate petioles, and they are from 4 to 11 cm (1.6 to 4.3 in) in length and usually 5–7 millimeters in width. By the time the plant flowers, the basal leaves are usually withered, yet the stem leaves usually remain. The leaves along the stem range in length from 5 to 12 cm (2 to 5 in) and sometimes up to 18 cm (7 in). They are also grass-like and typically not as wide as those at the base, with width measurements from 1–6 mm. The leaves highest on the stem are either grass-like or awl-shaped with a tapering point, shorter from 1 to 5 cm (0.4 to 2.0 in), and very thin at only 1–2 mm wide.[3]

S. potosinum flower heads, pressed and dried

The inflorescences of S. potosinum consist of a usual range of 3 to 20 flower heads in paniculiform arrays with their branches growing at 45–50° angles to the stem. Each head has a 1–4 cm (0.4–1.6 in) hairless peduncle with 1–4 bracts. The involucres are cylindric to hemispheric in shape and 5–7.3 mm in length. The phyllaries are in 2–3, sometimes up to 5, series, and awl-shaped to lanceolate.[3]

Its flowers have 14–27 white ray florets that are from 4.6 to 10.3 mm in length and 1.3–2 mm wide. There are usually 18–35 yellow disk florets with triangular spreading lobes when they bloom.[3]

Symphyotrichum potosinum has a base number of five chromosomes (x = 5)[5] with a diploid count of 10.[3]

S. potosinum specimen stored at Deaver Herbarium, Northern Arizona University. Collected 11 June 2016, Garden Canyon, Fort Huachuca, Huachuca Mountains, Cochise County, Arizona, at 1,844 m (6,050 ft).

The basionym (original scientific name) of Symphyotrichum potosinum is Aster potosinus A.Gray.[6] Its name with author citations is Symphyotrichum potosinum (A.Gray) G.L.Nesom.[2] The species was formally described in 1880 by American botanist Asa Gray from a specimen collected by E.Palmer and C.C.Parry,[lower-alpha 1] now the holotype and housed in the Gray Herbarium.[11] It is a member of the genus Symphyotrichum classified in the subgenus Astropolium.[12]

The word Symphyotrichum has as its root the Greek symphysis, which means "junction", and trichos, which means "hair".[13] The specific epithet potosinum is a Latinization of the Spanish word potosino for the Mexican state of San Luis Potosí where the holotype was found.[14]

The species' former genus, Aster, comes from the Ancient Greek word ἀστήρ (astḗr), meaning "star", referring to the shape of the flower. The word "aster" was used to describe a star-like flower as early as 1542 in De historia stirpium commentarii insignes, a book by the German physician and botanist Leonhart Fuchs. An old common name for Astereae species using the suffix "-wort" is "starwort", also spelled "star-wort" or "star wort". An early use of this name can be found in the same work by Fuchs as Sternkraut, translated from German literally as "star herb" (Stern Kraut).[15]