Flora of North America species comparison

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Senecio megacephalus

Senecio riddellii

large-head groundsel, rocky ragwort

Riddell's groundsel, Riddell's ragwort
Habit Perennials, (15–)30–50 cm (rhizomes woody, suberect or creeping). Subshrubs, 30–100 cm (taproots forming woody crowns).
Herbage

loosely arachno-tomentose, unevenly glabrescent.

glabrous.
Stems

single or clustered.

usually multiple (branching upward).
Leaves

progressively reduced distally; weakly petiolate;

blades lanceolate to narrowly oblanceolate, 10–18+ × 1–2(–3+) cm, bases tapered, margins entire or wavy (often with dark, cartilaginous denticles; mid leaves similar, smaller, sessile; distal leaves bractlike).

± evenly distributed (proximal often withering before flowering, pendulous);

sessile or obscurely petiolate;

blades linear-filiform (or irregularly pinnately divided into linear-filiform lobes), blades or lobes 4–9 cm × 1–5 mm, bases ± linear, ultimate margins entire.
Ray florets

± 13;

corolla laminae (5–)15–20 mm.

± 8;

corolla laminae (often falling early) 8–10 mm.
Phyllaries

± 21, 9–12(–14) mm, tips not notably blackened (short-hairy).

± 13, 7–10(–12+) mm, tips green.
Calyculi

of 5–8+ linear to filiform bractlets (lengths 1/2–7/8+ phyllaries).

usually of 3–8+ lance-linear to filiform bractlets (lengths 1/10–1/3 phyllaries).
Heads

usually 1 (sometimes subtended by 1–2 smaller heads).

5–20+ in close, corymbiform arrays (involucres campanulate, 7–10 mm diam.).
Cypselae

glabrous.

hirtellous.
2n

= 40.

= 40.

Senecio megacephalus

Senecio riddellii
Phenology Flowering summer. Flowering mostly mid summer–fall, occasionally spring.
Habitat Rocky, moist or drying sites, especially on mountain slopes Sandy or rocky open sites, especially drying, open, flood plains
Elevation 1500–2500 m (4900–8200 ft) 600–2500 m (2000–8200 ft)
Distribution
from FNA
ID; MT; WY; AB; BC
[BONAP county map]
from FNA
AZ; CO; KS; NE; NM; OK; SD; TX; WY
[WildflowerSearch map]
[BONAP county map]
Discussion

Senecio riddellii intergrades morphologically with S. spartioides. Typically, the former has larger heads with campanulate involucres 7–10 mm diam.; the latter has cylindric involucres rarely more than 6 mm diam.

Senecio riddellii is poisonous to livestock. It is now locally scarce because of efforts to eradicate it.

(Discussion copyrighted by Flora of North America; reprinted with permission.)
Source FNA vol. 20, p. 553. FNA vol. 20, p. 560.
Parent taxa Asteraceae > tribe Senecioneae > Senecio Asteraceae > tribe Senecioneae > Senecio
Sibling taxa
S. actinella, S. amplectens, S. ampullaceus, S. aphanactis, S. arizonicus, S. aronicoides, S. astephanus, S. atratus, S. bigelovii, S. blochmaniae, S. californicus, S. cannabifolius, S. clarkianus, S. crassulus, S. elegans, S. elmeri, S. eremophilus, S. ertterae, S. erucifolius, S. flaccidus, S. fremontii, S. hydrophiloides, S. hydrophilus, S. integerrimus, S. jacobaea, S. lemmonii, S. lugens, S. lyonii, S. mohavensis, S. multidentatus, S. neowebsteri, S. parryi, S. pattersonensis, S. pseudoarnica, S. pudicus, S. quaylei, S. rapifolius, S. riddellii, S. sacramentanus, S. scorzonella, S. serra, S. sheldonensis, S. soldanella, S. spartioides, S. sphaerocephalus, S. spribillei, S. squalidus, S. sylvaticus, S. taraxacoides, S. triangularis, S. viscosus, S. vulgaris, S. warnockii, S. wootonii
S. actinella, S. amplectens, S. ampullaceus, S. aphanactis, S. arizonicus, S. aronicoides, S. astephanus, S. atratus, S. bigelovii, S. blochmaniae, S. californicus, S. cannabifolius, S. clarkianus, S. crassulus, S. elegans, S. elmeri, S. eremophilus, S. ertterae, S. erucifolius, S. flaccidus, S. fremontii, S. hydrophiloides, S. hydrophilus, S. integerrimus, S. jacobaea, S. lemmonii, S. lugens, S. lyonii, S. megacephalus, S. mohavensis, S. multidentatus, S. neowebsteri, S. parryi, S. pattersonensis, S. pseudoarnica, S. pudicus, S. quaylei, S. rapifolius, S. sacramentanus, S. scorzonella, S. serra, S. sheldonensis, S. soldanella, S. spartioides, S. sphaerocephalus, S. spribillei, S. squalidus, S. sylvaticus, S. taraxacoides, S. triangularis, S. viscosus, S. vulgaris, S. warnockii, S. wootonii
Synonyms S. filifolius var. fremontii, S. riddellii var. parksii, S. spartioides var. fremontii, S. spartioides var. parksii, S. spartioides var. riddellii
Name authority Nuttall: Trans. Amer. Philos. Soc., n. s. 7: 410. (1841) Torrey & A. Gray: Fl. N. Amer. 2: 444. (1843)
Web links 
Unless otherwise noted, all data comes from the online version of the Flora of North America, who have made most of their content available via a Creative Commons license (CC BY 4.0).



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