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ASTERACEAE

SUNFLOWER FAMILY

David J. Keil, Family Editor and author, except as specified

Annual to tree
Leaves basal or cauline, alternate to whorled, simple to compound
Inflorescence: 1° inflorescence a head, each resembling a flower, 1–many, generally arrayed in cymes, generally subtended by ± calyx-like involucre; flowers 1–many per head
Flowers bisexual, unisexual, or sterile, ± small, of several types; calyx 0 or modified into pappus of bristles, scales, or awns, which is generally persistent in fruit; corolla radial or bilateral (rarely 0), lobes generally (0)4–5; stamens 4–5, anthers generally fused into cylinder around style, often appendaged at tips, bases, or both, filaments generally free, generally attached to corolla near throat; pistil 1, ovary inferior, 1-chambered, 1-seeded, style 1, branches 2, generally hair-tufted at tip, stigmas 2, generally on inside of style branches
Fruit: achene, cylindric to ovoid, generally deciduous with pappus attached
Genera in family: ± 1300 genera, 21,000 species (largest family of dicots): worldwide. Largest family in CA. Also see tribal key to CA genera: Strother 1997 Madroño 44(1):1–28. See glossary p. 25 for illustrations of general family characteristics.

XYLORHIZA

DESERT-ASTER

Perennial, subshrubs, shrubs
Stems generally white, glabrous or hairy
Leaves simple, alternate, entire or toothed; midrib white
Inflorescence: heads radiate, solitary, peduncled; involucre bell-shaped or hemispheric; phyllaries graduated in several series; receptacle convex, naked
Ray flowers generally many; corollas white to blue or purple
Disk flowers many; corolla yellow; style tips linear, acute
Fruit linear to club-shaped, weakly compressed, covered with long, appressed hairs; pappus of many, unequal bristles
Species in genus: 8 spp: w North America:
Etymology: (Greek: woody root)
Reference: [Watson 1977 Brittonia 29:199–216]

Native

X. cognata (H.M. Hall) T.J. Watson

MECCA-ASTER

Shrub < 1.5 m
Stems generally short-glandular, glabrous in age
Leaves 1–5 cm, oblanceolate to ovate, glabrous to glandular, obtuse or acute, ± spiny-dentate or entire, not reduced upward
Inflorescence: peduncles 0–11 cm; phyllaries 8–19 mm, 0.8–2.2 mm wide, subglabrous to densely glandular, innermost < immediately preceding series
Ray flowers 20–30; tube 5–8 mm; ligule 1.8–2.5 cm, light blue
Disk flowers 40–80; corolla 7–9 mm
Fruit 3–4.5 mm; pappus bristles < or = 9.5 mm
Chromosomes: 2n=12
Ecology: Arid canyons
Elevation: 20–240 m.
Bioregional distribution: n Sonoran Desert (Riverside Co.)
Flowering time: Jan–Jun
Synonyms: Machaeranthera c. (H.M. Hall) Cronquist & D.D. Keck

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