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alkali aster, Chiricahua Mountain tansy-aster

Habit Annuals, 25–60 cm; taproots slender to thick.
Stems

1–12+, erect or ascending, straight and rigid, sometimes sprawling from base, branching from base and distally, glabrous, glaucous.

Leaves

mostly cauline;

sessile (± appressed);

blades oblanceolate, 20–30 × 3–5 mm, reduced distally, (thick, succulent) bases broadened, margins entire (incised to dentate in hybrids with A. parviflora) eciliate or with 1–8 cilia per side, apices linear, spiny-mucronate, glabrous;

distal subulate, entire.

Involucres

hemispheric, 10–12 × 10–16 mm (fresh).

Ray florets

50–80+;

laminae bluish purple to lavender, 10–12 mm, coiled after flowering.

Disc florets

45–100+;

corollas yellow, 3.5–5 mm.

Phyllaries

in 4–5 series, appressed, linear-lanceolate, 2–8 mm, bases whitish to tan, margins entire to laciniate, apices green, acute to acuminate, glabrous.

Heads

borne singly (terminal), often in loose, leafy, cymiform arrays.

Cypselae

oblanceoloid, 2.5–3 mm, 11–13-nerved per face, faces sparsely sericeous;

pappi: white, setose;

ray 3–3.5 mm;

disc 3–4 mm.

2n

= 10.

Arida riparia

Phenology Flowering Apr–Sep.
Habitat Low valleys, saline soils on mudflats, edges of playas
Elevation 1300–1400 m (4300–4600 ft)
Distribution
from FNA
AZ; NM; Mexico (Chihuahua, Coahuila, Durango, Zacatecas)
Discussion

Arida riparia is a distinctive species recognized by its V-shaped branching, narrow, succulent, somewhat appressed, spiny-tipped leaves, and relatively large heads. It is known to hybridize with A. parviflora in southeastern Arizona and adjacent New Mexico. Specimens with dentate leaf margins usually represent hybrids.

(Discussion copyrighted by Flora of North America; reprinted with permission.)

Source FNA vol. 20, p. 405.
Parent taxa Asteraceae > tribe Astereae > Arida
Sibling taxa
A. arizonica, A. blepharophylla, A. carnosa, A. mattturneri, A. parviflora
Synonyms Aster riparius, Machaeranthera riparia, Machaeranthera sonorae
Name authority (Kunth) D. R. Morgan & R. L. Hartman: Sida 20: 1414. (2003)
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