1a On above-ground parts => 3

1b On roots => 2

2a Roots close to the surface with an expanded weak swelling, centrally with a wide canal, protruding into the stem and containing a caterpillar. Jacobaea erucifolia, J. vulgaris: Epiblema scutulana

2b Root with small, nodule- or spindle-shaped, cylindrical galls, up to 6 mm long S. vulgaris: Meloidogyne hapla

3a On capitula => 23

3b On vegetative organs => 4

4a Extensive malformations of plant parts; or galls on shoot tips, buds or leaves => 8

4b Galls on stems => 5

4c Stem and leaves greatly swollen and distorted by vivid orange aecia; long, dark brown to black telia may rarely be found at the same time; frequent. Jacobaea vulgaris, Pallenis maritima, Pericallis hybrida, Senecio spp.: Puccinia lagenophorae

4d Stem and leaves slightly swollen and distorted; with powdery orange uredinia and waxy reddish telia; rarely recorded. Senecio s.lat.: Coleosporium senecionis

5a Swelling elongate, situated at different positions. A caterpillar with distinct head capsule lives in a canal in the pith, extending beyond the swelling. Stem close to the gall considerably stunted or completely degenerating, overgrown later on by lower lateral shoots => 7

5b Galls plump, inhabited by larvae lacking a distinct head capsule => 6

6a Stem with padding, often developed on one side, distinctly curved swelling. Galls predominantly in upper stem part, sometimes with several, ± amalgamating. Several yellowish-white jumping larvae. Jacobaea aquatica, erratica, erucifolia, paludosa, vulgaris; Senecio leucanthemifolius subsp. vernalis, sylvaticus, viscosus, vulgaris: Contarinia jacobaeae

= White, non-jumpin, larvae of the gall midge Jaapiella crinita develop as inquilines in galls of Contarinia jacobaeae

6b Stem swollen immediately under the inflorescence. One yellow larva. Jacobaea vulgaris, Senecio sylvaticus: Unidentified dipteran

6c Several rotund galls, up to 10 mm long variously shaped and situated terminally on main- and lateral shoots; also in the inflorescences as well as in buds, petioles and capitula; often extending into neighbouring organs. Centrally one or several large larval chambers with pale yellow to flesh-coloured larvae. Jacobaea vulgaris; Senecio nemorensis, ovatus incl. subsp. stabianus, sarracenicus, sylvaticus: Contarinia aequalis

7a Stem over the galled part ± irregularly thickened, with spindle- to almost nodule-shaped bulges. Galls up to 30 mm long, predominantly on apical sites, with an ejection hole for frass, sometimes bursting. Leaves degenerating. One ivory- to dirty olive-green, black-headed caterpillar. Jacobaea aquatica; Senecio nemorensis, ovatus incl. subsp. stabianus, sarracenicus, sylvaticus: Platyptilia nemoralis

7b Stem in upper third, sometimes immediately below the inflorescence, over a length of 25–35 mm, spindle-shaped to cylindrically swollen. One reddish-yellow caterpillar, the underside paler, with pale brown head capsule. Jacobaea erucifolia, vulgaris; ? Senecio sylvaticus.: Cochylis atricapitana

7c Similar stem gall, in Jacobaea aquatica, vulgaris; Senecio nemorensis, sarracenicus: Platyptilia isodactylus

8a Wart- bulge- or cup-shaped galls on leaves, induced by fungi or psyllids => 16

8b Malformations of large plant parts or galls on shoot tips or lateral buds => 9

9a Malformations on buds or on shoot tips => 15

9b Extensive malformation of the complete plant or malformation of several leaves on the shoot tips => 10

10a Malformations by aphids or cercopids => 11

10b Early infected stems markedly stunted; basally over large extension spongy, swollen, pale green, with rugose, partially undulating surface. Later infestation results in locally expanded one- or often all-sided stem swellings, in conjunction with twisting and curving. Involved organs severely stunted; sometimes also irregularly thickened at the base. Senecio vulgaris, viscosus: Ditylenchus dipsaci

11a Malformations of various kind, usually not specific for the inducer; aphids => 12

11b Large areas on the intensively green site of infestation, strongly bent at leaf apex and ± deflected at margin, curled. Infestation of young stem parts results in stunting and bending of the internodes with ± clustering of disfigured leaves. Senecio s.lat.: Philaenus spumarius

12a Aphids dark green to black => 14

12b Aphids brighter => 13

13a Leaves ± stunted, margins loosely deflected or rolled, curled. Often many per plant, resulting sometimes in conspicuous malformations. Aphid 1.1–2 mm long, bright- to yellow-green. Senecio s.lat.: Brachycaudus helichrysi

13b Leaf blades curled, margins deflected; similar malformations on often many, ± clustered leaves on tips of shoots. Aphid 2–2⅓ mm, greenish to yellowish with large glossy black dorsal patch. Jacobaea aquatica, vulgaris; Senecio spp: Brachycaudus cardui

14a Leaves clustered at tips of shoots and young inflorescence compact, strongly malformed. Leaf blades bent, loosely rolled or curled; capitula ± stunted and disfigured. Aphid 1.5–2 mm long, dirty green to black. Antennae a little longer than half the body length; tibiae black. Jacobaea aquatica, vulgaris; Senecio gallicus, ovatus subsp. stabianus, vulgaris: Aphis jacobaeae

14b Terminal leaves clustered on stunted shoots, deformed, loosely curved downwards and curled. Young plants sometimes completely disfigured. Aphid about 2.5 mm long, dark grey-green to dull black. Antennae half the body length. Legs yellowish annulated. Jacobaea maritima, vulgaris; Senecio spp.: Aphis fabae

15a Shoot tips or lateral buds stunted; Leaves markedly stunted in their development. ± wrinkled and discoloured, heavily whitish pubescent, clustered into an elongated, bud-like shoot. Jacobaea aquatica, vulgaris; Senecio sylvaticus, vulgaris: Aceria leioprocta

15b Terminal- or lateral buds transformed into an irregular, rotund-barrel-shaped, succulent gall. A large chamber inside containing pale-yellow to flesh-coloured larvae. Jacobaea vulgaris; Senecio nemorensis, ovatus incl. subsp. stabianus, sarracenicus, sylvaticus: Contarinia aequalis

16a Wart- or bulge-shaped fungus galls => 17

16b Leaf blade curled, with weak embossment protruding on the upper side. S. nemorensis, ovatus: Trioza senecionis

17a Galls conspicuous; occupied at an early stage by a dusting of sori => 18

17b Galls wart-shaped, coalesced, almost 1 mm long; golden yellow; often many on the underside of basal leaves or on the base of young stems. Senecio vulgaris: Synchytrium aureum

18a Sori ± clearly thickened, bearing aecia => 20

18b Leaf blade often with rotund, bulging pads on the underside or leaf veins, petioles and axial parts with ± spindle-shaped, telia bearing elevations => 19

19a Dark brown, small sori, often occurring on the underside of the leaves, sometimes clustering into larger groups, in that case clearly cecidogenic. Jacobaea alpina, aquatica, subalpina, vulgaris; Senecio spp.: Puccinia expansa

19b Rotund, only slightly- or not thickened, ± yellowish margined sori, 5–10 mm wide, on leaf underside. Senecio ovatus, sarracenicus: Puccinia uralensis

20a Host-alternating fungi, which develop yellowish swellings on Senecio species, bearing their aecia and partially pycnidia => 21

20b Fungus host-specific; on the host only sori with telia develop, besides aecia. Swellings often insignificant. Aecia with whitish peridium; in irregular, loose, smaller groups, rarely extended, on the leaf underside. Jacobaea alpina, aquatica, subalpina, vulgaris; Senecio spp.: Puccinia expansa

21a Aecia on Tephroseris spp. => 22

21b Various rust fungi; recorded from:

a Senecio viscosus, vulgaris: Puccinia opizii

b Jacobaea vulgaris; Senecio viscosus, vulgaris: Puccinia schoeleriana

c Senecio nemorensis, ovatus: Puccinia silvatica

d Jacobaea alpina, aquatica, erucifolia, paludosa, vulgaris; Senecio ovatus, sylvaticus, viscosus, vulgaris: Puccinia senecionis-acutiformis

22a Aecia on the leaf undersides in rotund, often yellow-brown, violet-margined spots. Tephroseris longifolia subspp. brachychaeta, gaudini: Puccinia baldensis

22b Aecia usually on the leaf underside in rotund yellow spots. Tephroseris helenitis, palustris: Puccinia eriophori

= Aecidium senecionis-crispati has been described from Tephroseris crispa.

23a Swollen capitula on otherwise normally developed plants => 24

23b Clustered, shortened, leafy and greened capitula on ± atrophied plants. Jacobaea aquatica, J. erucifolia, J. vulgaris, Senecio sylvaticus, vulgaris: Unidentified ? gall mite

= Stunted but not greened flowers of Jacobaea vulgaris are caused by an unidentified thrips

24a Larvae inside the galls => 25

24b Larvae between the achenes. Capitula not opening, markedly swollen, rotund to broad ovoid, the base especially succulent thickened and yellowish to ± reddened there. Several yellowish-white, jumping larvae. Mainly on Jacobaea vulgaris; less frequent on Jacobaea aquatica, erratica, erucifolia, paludosa, vulgaris; Senecio leucanthemifolius subsp. vernalis, sylvaticus, viscosus, vulgaris.: Contarinia jacobaeae

24c Thickened capitula of S. ovatus containing yellowish, non-jumping larvae of Dasineura senecionis

24d Flower head only inconspicuously swollen bearing a cone of froth which covers a fly maggot. Jacobaea aquatica, incana subsp. carniolica, vulgaris; Senecio ovatus; Tephroseris crispa: Botanophila seneciella

25a Capitula usually only slightly swollen. Larvae in the thickened receptacle => 26

25b Major part of the flower head deformed to form a succulent gall. All organs more or less incorporated in the gall formation, which may extend to the stalk. Inside a large cavity containing pale yellow to succulent-red larvae. Jacobaea vulgaris; Senecio nemorensis, ovatus incl. subsp. stabianus, sarracenicus, sylvaticus: Contarinia aequalis

26a Larvae lacking distinct head capsule and legs => 27

26b Larvae with head capsule and thoracic legs in the slightly enlarged receptacle. S. viscosus: Unidentified lepidopteran

27a Capitula at base often heavily swollen on all sides and discoloured yellow-green, not opening, usually large cone-shaped. Fruits usually withered. Containing a single larva. Senecio s.lat.: Sphenella marginata

27b Receptacle externally only weakly swollen, often on one side, and hardened; later bulging upwards locally. Capitula not opening, mostly cylindrical to narrow cone-shaped. Containing a single larva. Senecio s.lat.: Trupanea stellata