Citation: L., Sp. Pl. 866 (1753).

Derivation: Latin senex, an old man; referring to the white pappus.

Synonymy: Not Applicable

Common name: Senecios.

Description:
Erect annual or perennial herbs or shrubs, rarely climbers; stems solitary or many from a common base; leaves alternate, simple, petiolate or sessile, entire or variously divided.

Capitula few to many usually in a terminal corymbose panicle, homogamous discoid or heterogamous and then radiate or discoid (erechthitoid); involucres uniseriate, cylindrical or campanulate, usually with a calyculus of few to many bracteoles crowded around the base; involucral bracts free or interlocking, rarely fused, usually subequal, alternating bracts with broad scarious margins; receptacle flat, pitted, the pit margins naked or variously raised and scaly; marginal florets fertile, either undifferentiated, bisexual and tubular, or female and then ligulate or filiform; ligules usually 4- or 5-veined, bright-yellow, rarely purple or white; disk florets bisexual, fertile, usually 5-merous, corolla yellow, distally campanulate; anthers obtuse, acute or shortly tailed basally, with a triangular to ovate-deltoid apical appendage; staminal filaments each pear-shaped distally; style branches broadly linear, flattened; style apices truncate or rarely domed, partially or completely encircled by spreading marginal papillae; stigmatic surface of 2 marginal lines, rarely superficially continuous.

Achenes usually subcylindrical, variously pubescent or rarely glabrous; pappus white or sometimes straw-coloured, usually of numerous deciduous capillary bristles that are uniform or dimorphic (all barbs erect or some with retrorse barbs at the apex), sometimes of uniform stout persistent bristles.

Distribution:  An estimated 1,500 species throughout the world and reputed to be the largest genus of flowering plants, approximately 50 species native and at least 7 adventive in Australia, occurring throughout the continent but most frequent and diversified in southern and eastern regions.

Biology: No text

Taxonomic notes: Recent treatments of the tribe Senecioneae recognise 2 broad groups of genera allied either to Cacalia or Senecio (Jeffrey (1979) Kew Bull. 34:49-58; Jeffrey et al. (1977) Kew Bull. 32:47-67; Nordenslam (1977) in Heywood et al. The biology and chemistry of the Compositae, vol. 2, pp. 799-830; Nordenslam (1978) Opera Bot. 44:1-84). Several Australian species of Senecio possess one or more cacalioid characteristics, but resolution of the generic status of these species, with perhaps the exception of Senecio gregorii, must await a more precise definition of Senecio sensu stricto.

Key to Species:

1. Capitula radiate, heterogamous; marginal florets female, with conspicuous and spreading ligules (ligules reduced in S. glossanthus and some hybrids); disk florets bisexual, distally campanulate, more numerous than the female florets	GROUP A.
1. Capitula non-radiate
2. Florets all bisexual, distally campanulate, exserted several mm beyond the involucre and conspicuously yellow at anthesis	GROUP B.
2. Florets not all bisexual, scarcely exserted and inconspicuous at anthesis; those towards the margin female or with non-polliniferous staminodes, filiform; central florets bisexual, distally campanulate, usually fewer than the female florets	GROUP C.
GROUP A (species 1-11, capitula radiate)
1. Calyculus of 6 or more bracteoles, rarely 4 or 5 in some but not all capitula
2. Ligules purplish or reddish, rarely white	S. elegans 3.
2. Ligules yellow
3. Leaves sparsely or densely white-tomentose beneath; bracteoles of the calyculus linear or narrowly triangular
4. Involucral bracts more than 17; involucre more than 4 mm wide; ligules 4-7 mm long, entire	S. pterophorus 11.
4. Involucral bracts fewer than 17; involucres less than 4 mm wide; ligules 1-5 mm long, entire to deeply lobed apically . S. pterophorus hybrids 11
3. Leaves glabrous or with scattered hairs on both surfaces; bracteoles of the calyculus lanceolate to ovate-deltoid
5. Capitulum, including the ligules, more than 1 cm diam.; ligules 7-12 mm long, spreading	S. lautus 7.
5. Capitulum, including the ligules, less than 1 cm diam.; ligules 2-4 mm long, usually recurved	S. xorarius 10.
1. Calyculus of 5 or fewer bracteoles, rarely 6 or 7 in some but not all capitula
6. Ligules less than 5 mm long
7. Slender ephemeral herb	S. glossanthus 4.
7. Perennial shrubs
8. Leaves linear, margins strongly revolute; low plants from a horizontal rhizome	S. behrianus 2.
8. Leaves narrowly to broadly oblanceolate; tall plants from a single rootstock	S. pterophorus hybrids 11.
6. Ligules more than 5 mm long
9. Involucre of fused membranous bracts, splitting irregularly to release the achenes	S. gregorii 5.
9. Involucre of free usually interlocking bracts
10. Leaves spathulate or oblanceolate, sessile, glaucous
11. Inflorescence of 10-50 capitula, rarely fewer; bracts of the peduncles broadly clasping; ligules 7-15 mm long, usually 4-8-nerved	S. magnificus 8.
11. Inflorescence of 1-3 rarely 4-10 capitula; bracts of the peduncles narrowed basally; ligules 15-25 mm long, usually 14-18-nerved	S. megaglossus 9.
10. Leaves petiolate and rhombic or subpetiolate and pinnatisect
12. Leaf blade dentate, rhombic	S. angulatus l.
12. Leaf blade pinnatisect, oblong-ovate	S. jacobaea 6.
GROUP B (species 12-18, capitula homogamous discoid)
1. Involucral bracts 7-10, usually 8; florets 9-14, rarely 15 or 16
2. Leaves palmately veined, petiolate, with reniform stipules	S. mikanioides 16.
2. Leaves pinnately veined
3. Leaves petiolate, blade denticulate, white-tomentose, below	S. hypoleucus 15.
3. Leaves sessile, entire, toothed or pinnatisect, glabrous, cobwebby or hoary below
4. Leaves pinnatisect into filiform or linear segments	S. anethifolius 12.
4. Leaves entire or toothed
5. Venation of leaves intricately reticulate, often dark when dry, leaves glaucous or dark-green above, glabrous or sparsely cobwebby below	S. odoratus 17.
5. Venation of leaves not conspicuous, rarely dark when dry, leaves green or becoming glaucous, glabrous or hoary above and below	S. cunninghamii 13.
1. Involucral bracts 11-23; florets 15-70
6. Involucral bracts 11-14, rarely 16; woody perennial shrub	S. gawlerensis 14.
6. Involucral bracts 18-23; rather succulent annual herb.	S. vulgaris 18.
GROUP C (species 19-29, capitula heterogamous discoid)
1. Involucral bracts 16-20; leaves narrow
2. Lower leaves usually remotely toothed, sometimes entire or denticulate, acute; involucral bracts 7-8.5 mm long; achenes c. 2 mm long, blackish with white hairs	S. squarrosus 28.
2. Lower leaves usually entire, sometimes remotely toothed, apiculate; involucral bracts 10-13 mm long; achenes 4.2-6 mm long, brownish densely and minutely hairy	S. macrocarpus 23.
1. Involucral bracts 8-14; leaves various
3. Involucral bracts 8 or 9, rarely 10 or 11 in some but not all capitula
4. Leaves subentire or evenly denticulate	S. minimus 24.
4. Leaves coarsely lobed or irregularly toothed
5. Stems and often the leaves a dark reddish-purple, hispidulous; leaves lobed with the axes essentially perpendicular to the midrib; lobes denticulate	S. picridioides 25.
5. Stems and leaves green, glabrate; leaves lobed with the axes inclined forward at 35-40º from the midrib; lobes serrulate	S. biserratus 19.
3. Involucral bracts 11-14, rarely 10 in some but not all capitula
6. Leaves c. 3 times as long as broad, margins irregularly lacerate; plants glabrous	S. laceratus 22.
6. Leaves more than 3 times longer than broad, margins not lacerate; pubescence various
7. Leaves glabrous or sparsely hairy when young, runcinately pinnatifid, the segments retrorse	S. runcinifolius 27.
7. Leaves pubescent, not runcinately pinnatifid
8. Mid-stem leaves linear or narrowly lanceolate, entire, denticulate or remotely toothed
9. Hairs of the leaves and the stems without a multicellular base, long and slender, closely appressed to the plant surface; achenes slender, attenuate-rostrate apically, 2.5-4 mm long	S. quadridentatus 26.
9. Hairs of the leaves and the stems with a multicellular base, the long slender apices somewhat elevated from the plant surface; achenes plump, cylindrical, 2.2-2.5 mm long	S. tenuiflorus 29.
8. Mid-stem leaves oblanceolate or obovate, toothed or irregularly lobed
10. Upper leaf surface scabrous, hairs mainly short, stout, tuberculate; inflorescence lax at maturity; involucre glabrous or glabrescent	S. hispidulus 21.
10. Upper leaf surface not scabrous, hairs softly cobwebby or woolly; inflorescence dense at maturity; base of the involucre woolly	S. glomeratus 20.

Author: Prepared by M. E. Lawrence and R. O. Belcher