Senecio
Sp. Pl. 2: 866. 1753.
Gen. Pl. ed. 5, 373. 1754.
Annuals, biennials, perennials, subshrubs, or shrubs, 5–100(–250+) cm (perennating bases taprooted, fibrous-rooted, branched caudices, or suberect to creeping rhizomes; roots often fleshy, seldom branched; herbage glabrous or hairy, often glabrescent at flowering). Stems single or clustered, erect to lax (simple or branched). Leaves basal and/or cauline; alternate; petiolate or sessile (bases sometimes clasping); blades subpalmately to pinnately nerved, mostly ovate or deltate to oblanceolate, lanceolate, linear, or filiform (and most intermediate shapes), rarely suborbiculate (sometimes palmately or pinnately lobed to 2–3-pinnatifid), ultimate margins entire or denticulate to serrate or toothed (sometimes with relatively many callous denticles or teeth), faces glabrous or hairy (usually arachnose to tomentose, often glabrescent). Heads (sometimes nodding) usually radiate or discoid (rarely quasi-disciform), usually in corymbiform to cymiform, sometimes paniculiform or racemiform, arrays (sometimes from axils of distal leaves), sometimes borne singly. Calyculi usually of 1–8+ bractlets (bractlets often intergrading with distal peduncular bracts, mostly 1/5–1/2+ times phyllaries), sometimes 0. Involucres mostly cylindric or turbinate to campanulate, 5–15(–40) mm diam. Phyllaries persistent, usually ± 5, 8, 13, or 21 [34] in (1–)2 series, distinct (margins interlocking), erect (often reflexed in fruit), mostly oblong to lanceolate or linear, subequal or equal, margins usually scarious. Receptacles flat to convex, foveolate, epaleate. Ray florets usually ± 5, 8, 13, or 21 [34], pistillate, fertile, sometimes 0; corollas usually yellow, sometimes ochroleucous or white, rarely reddish to purplish (laminae sometimes barely surpassing phyllaries; peripheral pistillate florets usually 0, sometimes 1–8+; corollas usually yellow, sometimes ochroleucous or white). Disc florets (5–)13–80+, bisexual, fertile; corollas usually yellow, rarely ochroleucous, white, reddish, or purplish, tubes shorter than to equaling campanulate throats, lobes 5, erect to recurved, usually ± deltate; style branches stigmatic in 2 lines, apices usually truncate-penicillate. Cypselae cylindric or prismatic, usually 5-ribbed or -angled, glabrous or hairy (especially on ribs or angles, hairs sometimes myxogenic); pappi usually persistent (fragile), sometimes readily falling, of 30–80+, white to stramineous, barbellulate to smooth bristles. x = 10.
Distribution
Nearly worldwide, mostly in warm-temperate, subtropical, and tropical regions at mid and upper elevations.
Discussion
Species 1000+ (55 in the flora).
The concept of Senecio in traditional North American floristics stems from nineteenth century botanists who saw the genus as a diverse assemblage held together by similar morphologies of the heads and florets. Studies in the past two decades have shown Senecio in the broad sense to be a collection of separate lineages; a better taxonomy is to be had by treating the lineages as genera. Some of the lineages were recognized in the past as infrageneric assemblages. A treatment of Senecio by T. M. Barkley (1978) reflected the traditional circumscription of the genus; a narrower circumscription is used here. Present concepts, plus a catalogue of genera, were presented by Barkley (1999).
The “species-groups” recognized here are given names purely as a matter of convenience; the groups and their names are intentionally given no formal taxonomic status (T. M. Barkley 1978). Some of the groups may represent natural evolutionary alliances; that remains to be clarified.
The following taxa are not established members of the flora but are nonetheless noteworthy:
Senecio brasiliensis (Sprengel) Lessing var. tripartitus (de Candolle) Baker is a South American weed of disturbed sites, introduced on the Gulf Coast near Pensacola, Florida, in 1893–1894. Its presence was discussed by J. M. Greenman (1917) and by L. J. Uttal (1982), both of whom treated it as Senecio canabinaefolius Hooker & Arnott. It is toxic to livestock; it seems not to have persisted in the flora.
Senecio bicolor (Willdenow) Viviani (S. cineraria de Candolle) is one of the plants called “dusty miller” in the horticultural trade. It occasionally persists in the flora after cultivation.
Species of the African genus Euryops are commonly cultivated in California and Florida and, to a lesser extent, in other warm areas of the flora. They would key here to Senecio. They are shrubs with leaves dissected or prominently toothed, phyllaries connate for the proximal third of their lengths, and yellow corollas. Apparently none persist for long after cultivation.
Relatively recent collections from low-lying (50–100 m), seasonally wet, disturbed areas in Orange and San Diego counties, California, have included semi-weedy perennial herbs or subshrubs 100–200 cm that are initially arachnose to tomentose, soon glabrescent, and have oblanceolate to linear or filiform leaves (2–7 cm), notably small heads in corymbiform arrays, ± 13 phyllaries 3–4 mm, and 7–8 ray florets with corolla laminae 2–3 mm. G. L. Nesom (pers. comm.) has suggested that these plants are Senecio linearifolius A. Richard, a native of Australia and Tasmania.
References to shapes, sizes, bases, margins, induments, etc., of “leaves” in keys and descriptions refer to principal (largest, most conspicuous) leaves at flowering unless otherwise indicated.
Selected References
Lower Taxa
Keys
Key to Groups of Senecio Species, Exceptional Species, and Segregate Genera
| 1 | Corollas deep reddish to purplish (California) | Senecio elegans |
| 1 | Corollas usually yellow, rarely orange, ochroleucous, or whitish | > 2 |
| 2 | Leaves (basal usually present at flowering, mid and distal leaves usually progressively smaller, mid-stem leaves sometimes equaling basal) | > 3 |
| 2 | Leaves (basal usually withering before flowering, cauline leaves ± equal in size, usually evenly distributed or concentrated distally) | > 7 |
| 3 | Heads (usually nodding, at least in bud, if erect, mid-stem leaves clasping and phyllary tips black) | Group 1. Amplectentes |
| 3 | Heads (usually erect or nearly so; if nodding, plants not with both clasping mid-stem leaves and black-tipped phyllaries) | > 4 |
| 4 | Perennials (usually with rhizomes or erect caudices, sometimes taprooted; lateral roots fibrous, branched); basal and proximal leaves entire or dentate to pinnate, ultimate margins rarely with callous denticles (chromosome numbers: 2n = 44 or 46, or numbers derived therefrom) | Packera |
| 4 | Perennials (with lateral to suberect rhizomes or abruptly shortened, buttonlike caudices; lateral roots mostly fleshy-fibrous, seldom branched); basal and proximal leaves entire or repand-dentate, margins often with callous denticles (chromosome numbers: mostly 2n = 40 or numbers derived therefrom) | > 5 |
| 5 | Perennials (caudices buttonlike) | Group 3. Integerrimi |
| 5 | Perennials (caudices branched or plants rhizomatous) | > 6 |
| 6 | Phyllaries (adaxially glabrous or sparsely puberulent) | Group 2. Lugentes |
| 6 | Phyllaries (adaxially villous) | Tephroseris |
| 7 | Involucres (20–)25–40 mm diam. (northern beaches and shorelines) | Senecio pseudoarnica |
| 7 | Involucres 3–15+ mm diam. (typically mesic to xeric sites) | > 8 |
| 8 | Subshrubs or shrubs (if but weakly woody, with upward-branching aspects of shrubs) | > 9 |
| 8 | Annuals, biennials, or perennials (caudices sometimes ± woody) | > 10 |
| 9 | Leaves sessile or obscurely petiolate (bases not clasping), linear-filiform or pinnately parted into linear-filiform lobes | Group 4. Suffruticosi |
| 9 | Leaves petiolate (proximal) or sessile, lanceolate to lance-linear (bases of at least mid leaves expanded, clasping) | Senecio lemmonii |
| 10 | Herbage viscid-pubescent | > 11 |
| 10 | Herbage glabrous or hairy, not viscid | > 12 |
| 11 | Leaves petiolate (pinnatisect to pinnatifid), 20–70 cm | Senecio viscosus |
| 11 | Leaves weakly petiolate (not pinnatisect to pinnatifid, margins dentate), 8–12 cm | Senecio parryi |
| 12 | Annuals, biennials, or perennials (without prominent caudices or rhizomes) | Group 5. Annui |
| 12 | Perennials (with well-developed caudices or rhizomes) | > 13 |
| 13 | Leaves 2–3-pinnatifid | Senecio jacobaea |
| 13 | Leaves 0–1-pinnatifid (ultimate margins entire to lacerate, lobes sometimes toothed) | > 14 |
| 14 | Leaves not lobed (margins dentate to serrate or subentire) | Group 6. Triangulares |
| 14 | Leaves pinnatifid or subpalmately lobed (ultimate margins entire or dentate to serrate) | > 15 |
| 15 | Plants (50–)100–150 cm (rhizomes fibrous-rooted); ray florets ± 5, corolla laminae ca. 10 mm (Aleutian Islands) | Senecio cannabifolius |
| 15 | Plants 30–80(–120) cm (caudices branched); ray florets ± 13, corolla laminae 12–15 mm | Senecio erucifolius |
Group 1. Amplectentes
| 1 | Ray florets usually 0 (if present, corolla laminae barely surpassing phyllaries) | > 2 |
| 1 | Ray florets ± 8 or 13 (corolla laminae well surpassing phyllaries, sometimes 0 in S. taraxacoides) | > 5 |
| 2 | Plants relatively robust, (20–)40–80(–120+) cm (involucres 10–15 mm diam.) | Senecio bigelovii |
| 2 | Plants seldom robust, (5–)20–50(–80+) cm (involucres to 10 mm diam.) | > 3 |
| 3 | Leaves narrowly lanceolate to lance-linear (lengths ca. 5 times widths, bases tapered to weakly defined petioles) | Senecio pudicus |
| 3 | Leaves lanceolate to triangular-ovate or suborbiculate (lengths mostly 1.5–2 times widths, bases contracted to distinct petioles) | > 4 |
| 4 | Leaves 3–10(–15) × 1.5–4 cm (herbage sparsely pubescent to tomentose, especially on abaxial leaf faces and among heads) | Senecio sacramentanus |
| 4 | Leaves 2–4(–5) × 2.5–3 cm (herbage glabrous) | Senecio spribillei |
| 5 | Heads usually erect (weakly, if at all, nodding) | > 6 |
| 5 | Heads usually nodding (at least in bud) | > 7 |
| 6 | Plants 10–20(–30) cm, glabrescent (with at least some indument at flowering; stems in semi-cespitose clumps from trailing, branching rhizomes) | Senecio elmeri |
| 6 | Plants (15–)20–50(–70) cm, glabrous (stems single or in loose clusters from ± woody caudices) | Senecio crassulus |
| 7 | Leaf margins dentate to incised (at least abaxial faces floccose-tomentose) | Senecio taraxacoides |
| 7 | Leaf margins subentire to dentate (if dentate, faces glabrous) | > 8 |
| 8 | Leaves ovate to ovate-orbiculate, 2.5–4.5 cm (lengths nearly equaling widths) | Senecio soldanella |
| 8 | Leaves lanceolate, oblanceolate, or ovate, 2–20+ cm (lengths 1–3 times widths) | > 9 |
| 9 | Herbage glabrous or sparsely, unevenly hairy (especially in and near leaf axils); leaves broadly lanceolate or lanceolate to oblanceolate, 10–20+ × 2–4(–5) cm | Senecio amplectens |
| 9 | Herbage floccose-tomentose, sometimes unevenly glabrescent; leaves lanceolate to oblanceolate or ovate, 4–8+ × 1.5–3 cm | Senecio neowebsteri |
Group 2. Lugentes
| 1 | Heads 1(–3) | > 2 |
| 1 | Heads (8–)10–60+ | > 3 |
| 2 | Leaves 3–7(–10) × 1–2(–3+) cm; laminae of ray corollas usually 8–10 mm (sometimes tubular, not expanded); cypselae hairy | Senecio actinella |
| 2 | Leaves 10–18+ × 1–2(–3+) cm; laminae of ray corollas 10–20 mm; cypselae glabrous | Senecio megacephalus |
| 3 | Ray florets 0 | > 4 |
| 3 | Ray florets usually 3–13 (sometimes 0 in S. scorzonella) | > 5 |
| 4 | Herbage floccose-lanate to tomentose; phyllaries ± 21 | Senecio astephanus |
| 4 | Herbage glabrous (glaucous); phyllaries (± 5) ± 8 | Senecio rapifolius |
| 5 | Stems often closely clustered (cauline leaves prominent, some nearly as large as or larger than basal leaves); heads 20–60+ (involucres 5–6 + mm diam.); phyllaries (±5) ± 8 | Senecio atratus |
| 5 | Stems usually single (cauline leaves usually smaller than basal); heads 3–30+ (involucres 8–12 mm diam.); phyllaries (± 8) ± 13 (± 21) | > 6 |
| 6 | Herbage glabrous (unevenly glaucous) | Senecio wootonii |
| 6 | Herbage usually floccose to tomentose and/or glabrescent (never glaucous) | > 7 |
| 7 | Leaf bases tapered (to broad, indistinct petioles); phyllaries usually ± 13, tips black | Senecio lugens |
| 7 | Leaf bases contracted (to distinct petioles); phyllaries ± 13 or ± 21, tips green, sometimes with minute black dots | > 8 |
| 8 | Leaf margins dentate (cauline leaves relatively small, bractlike); phyllaries ± 13; ray florets usually ± 5, sometimes 0 | Senecio scorzonella |
| 8 | Leaf margins usually entire, sometimes minutely denticulate; phyllaries ± 21; ray florets ± 13 | > 9 |
| 9 | Leaves ovate to subelliptic (at least basal adaxially purple; lengths 1.5–2 times widths) | Senecio arizonicus |
| 9 | Leaves oblanceolate to elliptic (abaxially green; lengths 2–3 times widths) | Senecio sphaerocephalus |
Group 3. Integerrimi, etc.
| 1 | Herbage arachnose, tomentose, or villous (at least when young; often glabrescent) | > 2 |
| 1 | Herbage usually glabrous (sometimes puberulent in leaf axils and among heads) | > 3 |
| 2 | Leaf margins repand-denticulate or laciniate to subentire; phyllaries ± 8 (± 13); ray florets 0 or 1–2 (disc florets 15–20) | Senecio aronicoides |
| 2 | Leaf margins mostly subentire; phyllaries usually (± 13) ± 21; ray florets usually ± 8 or 13, rarely 0 (disc florets 20–50) | Senecio integerrimus |
| 3 | Heads 4–12 (some proximal and mid-stem leaves about as large as the basal, bases usually clasping) | Senecio crassulus |
| 3 | Heads 20–80+ (proximal and mid-stem leaves smaller than the basal; distal leaves sessile, bases not clasping) | > 4 |
| 4 | Plants 40–100(–200) cm (herbage glaucous); leaves (fleshy-turgid): margins entire or denticulate (swamps, alkaline sites) | Senecio hydrophilus |
| 4 | Plants 30–100(–140) cm (herbage green, not glaucous); leaves (often firm, not fleshy-turgid): margins dentate to denticulate (wet hillsides and meadows, not swamps or alkaline sites) | Senecio hydrophiloides |
Group 4. Suffruticosi
| 1 | Calyculi: bractlets prominent (usually lengths of at least some to 1/2 phyllaries, if lengths less than 1/4 phyllaries, herbage woolly-tomentose to floccose, sometimes unevenly) | > 2 |
| 1 | Calyculi: bractlets 0 (or lengths less than 1/4 phyllaries; herbage glabrous or indument sparse and uneven, especially on adaxial leaf faces, in leaf axils, and among heads, never woolly-tomentose) | > 3 |
| 2 | Plants usually 40–120+ cm (leaves evenly distributed, seldom recurved, not subsucculent) | Senecio flaccidus |
| 2 | Plants usually 20–40 cm (leaves crowded distally, often recurved, ± thickish-turgid; gypseous soils of w Texas and adjacent New Mexico) | Senecio warnockii |
| 3 | Phyllaries ± 8 (involucres cylindric to narrowly campanulate, 3–6 mm diam.) | Senecio spartioides |
| 3 | Phyllaries ± 13 (involucres campanulate, 7–12 mm diam.) | > 4 |
| 4 | Leaves seldom lobed (linear-filiform, 3–12 cm × 1–3 mm) | Senecio blochmaniae |
| 4 | Leaves (some or all) usually pinnately lobed (lobes linear) | > 5 |
| 5 | Herbage sparsely hairy to glabrate, persistently hairy on abaxial leaf faces;phyllaries (± 13) ± 21, (5–)6–8 mm, tips black (California Channel Islands) | Senecio lyonii |
| 5 | Herbage glabrous; phyllaries ± 13, 7–10(–12+) mm, tips green | Senecio riddellii |
Group 5. Annui, etc.
| 1 | Herbage usually persistently villous; heads in dense, corymbiform arrays (Iowa, Minnesota, and northward) | Tephroseris (Tephroseris palustris) |
| 1 | Herbage usually glabrous or arachno-tomentose, floccose, puberulent, or viscid-glandular (seldom villous); heads usually in open, corymbiform or cymiform arrays | > 2 |
| 2 | Ray florets usually 0 (if 1–13+, corolla laminae 0.1–2+ mm, barely surpassing phyllaries, often recurved, coiled) | > 3 |
| 2 | Ray florets (± 8) ± 13 (corolla laminae 5–10+ mm, patent, seldom coiled) | > 7 |
| 3 | Herbage densely glandular-viscid | Senecio viscosus |
| 3 | Herbage glabrous or hairy (not glandular-viscid) | > 4 |
| 4 | Calyculi: bractlets 2–6 (tips black) | Senecio vulgaris |
| 4 | Calyculi: bractlets 0 or 1–5+ (tips green) | > 5 |
| 5 | Leaves (mid-stem) sessile (bases cordate-clasping, 1–2 cm wide) | Senecio mohavensis |
| 5 | Leaves (mid-stem) petiolate or sessile (bases weakly clasping) | > 6 |
| 6 | Plants (15–)40–80 cm (relatively coarse); phyllaries usually ± 13 or ± 21 | Senecio sylvaticus |
| 6 | Plants 5–20+ cm (relatively delicate); phyllaries usually ± 8, sometimes ± 13 | Senecio aphanactis |
| 7 | Leaves (all or some) lyrate-pinnatifid | > 8 |
| 7 | Leaves not lyrate-pinnatifid (margins subentire to dentate or incised) | > 9 |
| 8 | Calyculi: bractlets inconspicuous; phyllary tips green or lightly pink Genus | Packera (Packera tampicana, Packera glabella) |
| 8 | Calyculi: bractlets prominent (1–2 mm, tips black); phyllary tips black | Senecio squalidus |
| 9 | Heads (1–)10–40+ (taproots 1–3 cm, surrounded by branched, fibrous roots) | > 10 |
| 9 | Heads 3–20+ (taproots prominent) | > 11 |
| 10 | Plants 30–70+ cm; herbage loosely arachno-tomentose, unevenly glabrate or glabrescent; mid-stem leaves lanceolate, 3–10 cm (bases tapered or truncate, distal sometimes clasping) | Senecio ampullaceus |
| 10 | Plants 80–120 cm; herbage glabrous or glabrate; mid and distal leaves ovate to broadly lanceolate, 10–20 cm (bases clasping) | Senecio quaylei |
| 11 | Herbage glabrous or sparsely arachnose; phyllary tips often, not always, black; ray corolla laminae ca. 10 mm | Senecio californicus |
| 11 | Herbage permanently (sometimes unevenly) villous-tomentose (silvery); phyllary tips green; ray corolla laminae 5–6 mm | Senecio ertterae |
Group 6. Triangulares
| 1 | Plants to 10 cm (rhizomatous); leaves oblanceolate to lance-linear (2–4 cm) | Senecio pattersonensis |
| 1 | Plants 10–250 cm; leaves lanceolate, oblong, oblanceolate, obovate, ovate, spatulate, sublinear, suborbiculate, or triangular (mostly 4–25 cm). | > 2 |
| 2 | Plants (taprooted or caudices subrhizomatous, surmounting taproots); stems often lax andarching upwards | Senecio fremontii |
| 2 | Plants (fibrous-rooted; sometimes with persistent caudices, without evident taproots); stems mostly erect | > 3 |
| 3 | Leaves (at least mid cauline) pinnately lobed to irregularly incised or laciniate | > 4 |
| 3 | Leaves subentire to dentate (not lobed, incised, or laciniate) | > 5 |
| 4 | Herbage glabrous or glabrate (proximal leaves mostly withering before flowering) | Senecio eremophilus |
| 4 | Herbage tomentose, sometimes unevenly glabrescent (proximal leaves persistent) | Senecio clarkianus |
| 5 | Leaves ± triangular (bases usually ± truncate, sometimes tapered in acid-bogpopulations) | Senecio triangularis |
| 5 | Leaves ovate or lanceolate to sublinear (bases tapered or slightly rounded) | > 6 |
| 6 | Leaves narrowly lanceolate to sublinear (lengths 4.5–5 times widths; bases not clasping) | Senecio serra |
| 6 | Leaves ovate to lanceolate (lengths usually 2–3 times widths; bases of distal leaves clasping) | > 7 |
| 7 | Leaves usually 4–10 cm; heads 1–6 (British Columbia, Yukon) | Senecio sheldonensis |
| 7 | Leaves (7–)10–20+ cm; heads 4–12 (Arizona, New Mexico) | Senecio multidentatus |