Trans. Amer. Philos. Soc., n. s.7: 336. 1840
Calif., nw Mexico.
Species 6 (6 in the flora).
Five of the Pentachaeta species are restricted to California; the sixth occurs in southern California and adjacent Baja California. The plants are small, slender annuals with linear, entire, ciliate leaves, mostly yellow-rayed heads on long peduncles, and pappus bristles in multiples of five. D. D. Keck (1958) united Pentachaeta with Chaetopappa; G. S. Van Horn (1973) maintained it as a separate genus. Chaetopappa differs in various ways, including its consistently white (to bluish) rays, triangular to deltate style appendages (disc), and base chromosome number of 8. Pentachaeta is most closely related to the chiefly Californian annuals Rigiopappus and Tracyina (G. L. Nesom 1994).
|1||Ray florets 0, or pistillate florets 1–6, corollas either reduced to filiform, essentially elaminate tubes, or with inconspicuous, white laminae||> 2|
|1||Ray florets 5–70, laminae conspicuous, white or yellow||> 3|
|2||Stems diffusely branched; pistillate florets (4–)5(–6), corollas elaminate; disc corollas linear-tubular, lobes 3||Pentachaeta alsinoides|
|2||Stems simple to few branched; pistillate florets 0 or 1–3, corollas with or without laminae; disc corollas club-shaped, widened through limbs, abruptly contracted at lobes, lobes 5||Pentachaeta exilis|
|3||Ray laminae white, sometimes purplish-tinged; San Francisco Bay region||Pentachaeta bellidiflora|
|3||Ray laminae yellow; s California||> 4|
|4||Ray florets 7–12; largest leaves to 25 mm||Pentachaeta fragilis|
|4||Ray florets 14–52; largest leaves to 50+ mm||> 5|
|5||Pappus bristles 5–8; phyllaries ovate-elliptic to oblong-elliptic, glabrous or sparsely short-strigose; leaves 1(–3) mm wide||Pentachaeta aurea|
|5||Pappus bristles 8–12; phyllaries narrowly lanceolate, hirsuto-pilose; leaves 3–6 mm wide||Pentachaeta lyonii|
|Author||Guy L. Nesom +|
|Etymology||Greek pente, five, and chaite, long hair, alluding to 5 pappus bristles of type species, Pentachaeta aurea +|
|Illustrator||Barbara Alongi +|
|Reference||horn1973a + and nelson1975a +|
|Taxon name||Pentachaeta +|
|Taxon parent||Asteraceae tribe Astereae +|
|Taxon rank||genus +|
|Volume||Volume 20 +|