Xylorhiza

Nuttall

Trans. Amer. Philos. Soc., n. s. 7: 297. 1840.

Common names: Woody-aster
Etymology: Greek xylon, wood, and rhiza, root
Synonyms: Machaeranthera sect. Xylorhiza (Nuttall) Cronquist & D. D. Keck
Treatment appears in FNA Volume 20. Treatment on page 406. Mentioned on page 7, 19, 394.
 TaxonIllustrator 
FNA20 P43 Arida arizonica.jpegArida arizonica
Xylorhiza glabriuscula
Xylorhiza tortifolia var. tortifolia
Bee F. Gunn
Barbara Alongi
Barbara Alongi
FNA20 P44 Xylorhiza wrightii.jpegXylorhiza wrightii
Pyrrocoma crocea var. crocea
Barbara Alongi
Linny Heagy

Perennials, subshrubs, or shrubs, 10–80 (–150) cm (taproots woody, branched, caudices persistent). Stems (often white-barked) erect, branched, glabrous or villous to tomentose, sometimes stipitate-glandular. Leaves cauline; alternate; sessile or subpetiolate; blades mostly 1-nerved, linear to lanceolate or oblanceolate, oblong, or narrowly elliptic, margins entire or dentate-spinulose (apices acute), faces glabrous or sparsely tomentose to villous, sometimes stipitate-glandular. Heads radiate, borne singly (terminal on ebracteate peduncles). Involucres campanulate to hemispheric, 7–20 × 12–40 (–48) mm. Phyllaries 25–45 in 3–6 series, 1-nerved (keeled), narrowly lanceolate, unequal, proximally white-indurate, margins scarious (apices green, erect or spreading), abaxial faces glabrous or sparsely tomentose to villous, sometimes stipitate-glandular. Receptacles flat, pitted, epaleate. Ray-florets (4–) 12–60 (–85), pistillate, fertile; corollas white to light blue or purple (coiling at maturity). Disc-florets 30–140, bisexual, fertile; corollas yellowish, tubes slightly shorter to longer than narrowly funnelform throats, lobes 5, spreading, triangular; style-branch appendages lanceolate. Cypselae (brownish) fusiform to linear or ovoid, ± compressed to subterete, 4-ribbed, faces sericeous (hairs subappressed, long, silky); pappi persistent, of 30–45 tawny, stout, unequal, often flattened, barbellate, apically attenuate bristles in 2–3 series. x = 6.

Distribution

sw United States, nw Mexico

Discussion

Species 10 (9 in the flora).

Xylorhiza species were considered by A. Cronquist and D. D. Keck (1957) to be primitive members of the genus Machaeranthera, where they were recently maintained (Cronquist 1994). T. J. Watson (1977) and other contemporary botanists, however, have recognized Xylorhiza as a distinct genus characterized by the following features: perennial herbs, subshrubs, and shrubs from large, woody taproots with woody, branched, persistent caudices; large, single heads; long phyllaries with erect or spreading apices; white or bluish rays; large cypselae; and vernal flowering. The base chromosome number of Xylorhiza (x = 6) also contrasts with that of Machaeranthera (x = 4 or 5). Two sections were recognized by Watson: sect. Xylorhiza (subshrubs or perennial herbs) and sect. Californica T. J. Watson (shrubs, including X. cognata, X. orcuttii, and the Mexican endemic X. frutescens).

Key

1 Leaf margins (many of them) toothed > 2
1 Leaf margins all or nearly all entire > 5
2 Leaf blades mostly 1–2.5 mm wide, margins involute Xylorhiza confertifolia
2 Leaf blades mostly (2–)2.5–15 mm wide, margins flat > 3
3 Leaf blades linear-oblong to linear-lanceolate, bases truncate or rounded-auriculate Xylorhiza linearifolia
3 Leaf blades oblanceolate to oblong-spatulate, bases tapering > 4
4 Stems leafy for 2/3 + their lengths; peduncles 2–6 cm; involucres 7–14 × 12–25 mm Xylorhiza glabriuscula
4 Stems leafy in proximal 1/2 – 2/3; peduncles 5–20 cm; involucres 12–20 × 20–35 mm Xylorhiza venusta
5 Shrubs; stems branched to near apices; style-branch appendages shorter than stigmatic lines; s California > 6
5 Subshrubs or perennials; stems branched mostly in proximal 3/4; style-branch appendages longer or shorter than stigmatic lines; various regions > 7
6 Younger stems and branchlets stipitate-glandular; phyllaries loosely appressed, out-ermost stipitate-glandular (at least margins), innermost shorter than mid Xylorhiza cognata
6 Younger stems and branchlets eglandular; phyllaries tightly appressed; outermost glabrous, innermost equaling or longer than mid Xylorhiza orcuttii
7 Leaf blades spatulate to obovate or oblong, rarely elliptic; Texas Xylorhiza wrightii
7 Leaf blades linear-lanceolate to lanceolate, oblanceolate, or elliptic-oblong; n to w of Texas > 8
8 Leaf blades 2.5–6 mm wide, usually shallowly spinulose-toothed, sometimes entire; rays 13–17, white Xylorhiza cronquistii
8 Leaf blades 3–20(–25) mm wide, sharply spinulose-toothed; rays (15–)18–60(–85), usually lavender, seldom white Xylorhiza tortifolia
... more about "Xylorhiza"
stipitate-glandular +, sparsely tomentose +  and villous +
not tailed +, rounded +  and obtuse +
distinct +
subequal +
scarious +
usually triangular +  and linear +
usually deltate +  and lanceolate +
spiciform +, racemiform +, paniculiform +  and corymbiform +
indeterminate +  and determinate +
Guy L. Nesom +
Nuttall +
decurrent +
linear;lanceolate or oblanceolate oblong or narrowly elliptic +
rugulose +  and muricate +
Woody-aster +
not 2-lipped +  and actinomorphic +
yellowish +, white +  and light blue or purple +
fusiform +  and linear or ovoid more or less compressed +
fertile +  and bisexual +
fertile +  and bisexual +
sw United States +  and nw Mexico +
Greek xylon, wood, and rhiza, root +
sericeous +, stipitate-glandular +, sparsely tomentose +  and villous +
pistillate +, staminate +  and neuter +
winged +  and beaked +
dispersed +
indeterminate +
heterogamous +  and homogamous +
each +  and sessile +
4 cm40 mm <br />0.04 m <br /> (4.8 cm48 mm <br />0.048 m <br />) +
0.7 cm7 mm <br />0.007 m <br /> (2 cm20 mm <br />0.02 m <br />) +
campanulate;hemispheric +
1.2 cm12 mm <br />0.012 m <br /> (4 cm40 mm <br />0.04 m <br />) +
subpetiolate +  and sessile +
triangular +
dentate-spinulose +  and entire +
2-carpellate +
persistent +
lanceolate +
Trans. Amer. Philos. Soc., n. s. +
bearing subulate enations +, hairy +  and bristly +
concave;usually flat;conic +
watson1977b +
exalbuminous +
stipitate-glandular +, villous +  and tomentose +
appendaged +  and truncate +
papillate +  and smooth +
Machaeranthera sect. Xylorhiza +
Xylorhiza +
Asteraceae tribe Astereae +
shorter to longer +
80 cm800 mm <br />0.8 m <br /> (150 cm1,500 mm <br />1.5 m <br />) +
shrub +  and subshrub +