Plant Parasites of Europe

leafminers, galls and fungi

gallers on Taraxacum

Dichotomous table for gallers on Taraxacum

by Hans Roskam

1a On above-ground parts => 3

1b On root and root collar => 2

2a Roots with spindle-shaped to slightly nodular swellings, bearing isolated lateral roots. T. officinale: Meloidogyne hapla

2b Considerable tuft-like proliferations on root collar. T. officinale:
Agrobacterium tumefaciens

3a On inflorescences or capitula => 16

3b On leaves => 4

4a Exclusively or predominantly on petiole, midrib and main veins => 12

4b Extensive malformation, or localised galls on leaf blade => 5

5a Galls local, sometimes clustering into larger groups => 8

5b Leaf blade with extensive malformations of irregular composition => 6

6a Malformations caused by aphids or cercopids => 7

6b Leaf blade ± shrivelled, converging, curled, twisted or rolled upwards, roll may be haired; leaflets narrowed, margin sometimes lacerate. T. officinale: Aculus rigidus

6c Curled leaves, contain froth-covered nymphs. T. officinale: Philaenus spumarius

7a Leaf blades sometimes spirally twisted; contain dark brown aphids. T. officinale: Uroleucon taraxaci

7b Leaf blade curled, with bladder-like swellings. Aphid green. T. officinale: Aulacorthum solani

7c Little indentation of the leaf blade. T. officinale, palustre: Trioza dispar

8a Single galls more than 4 mm long => 11

8b Single galls smaller => 9

9a Leaf blades with many bulges or yellowish-white spots on the upper side caused by smut fungi => 10

9b Leaf blade on under-, more rarely on upperside, with many reddish-yellow to dark orange-red multicellular warts, up to 1 mm long; solitary or sometimes coalescing to expanded crusts. Also occurring on inflorescence stalks or even the involucre. T. officinale: Synchytrium taraxaci

10a Leaf blades with usually several rotund or irregularly margined, yellowish-green, later pale brownish spots, up to about 3 (4) mm across, sometimes slightly thickened. Containing yellowish spores. T. officinale: Entyloma picridis

10b Leaf blade often with many small protruding swellings on the upperside; containing flat larvae in the depressions on the underside. T. officinale, palustre: Trioza dispar

11a Leaf blade with flat circular blister, up to 5 mm across, usually several in a leaf; rim of gall becomes dark red or purple; containing a yellow-red larva under a translucent epidermis. T. campylodes, officinale: Cystiphora taraxaci

11b Swellings protruding on the leaf underside, bearing clustered yellow sporulating aecia; rotund to oblong-oval, up to about 10 (15) mm long, including the main venation, irregularly margined; often with yellowish or reddish discoloured rim. T. officinale: Puccinia dioicae

12a Galls glabrous, confined to the midrib or a main lateral vein; possible malformations of the leaf blade develop as secondary growth disturbances => 13

12b Spongy, soft swellings, visible on both sides, the surface undulate rugose, often pale green, sometimes ± reddened, extending variously from the mid- and lateral veins to the neighbouring, sometimes ± arched leaf blades. T. officinale: Ditylenchus dipsaci

13a Malformations remaining closed. Inducers inside the galls => 14

13b Swellings inconspicuous, ± elongate-oval, 2–3 mm long, predominantly bulging on the underside of the leaf; on the midrib with yellow rim; on the surface bearing 1-celled, brown spores. T. officinale: Puccinia hieracii

13c Minor bulges in the midrib caused by primary uredina, spermogonia lacking. T. officinale, serotinum: Puccinia taraxaci

14a Galls about 12 (15) mm long, causing localised swellings of the venation, predominantly on the central and apical part of the leaf blade => 15

14b Midrib swollen at the leaf base; swelling fading away into the central and apical part of disfigured leaf blade which is sometimes undulate in the galled area. Gall most prominent on the underside. A mining larva in the galled tissue, making a round exit hole which protrudes into the upper epidermis just before pupation. T. officinale: Phytomyza wahlgreni

15a Swellings abruptly discontinued; especially conspicuous on the underside, ± rotund to oblong-oval, about 2–6 mm across; often several partially or completely fused into a bulge up to 4 cm long; pale green or often reddened; soon tough-walled. individual swellings develop, each with one chamber and containing one white larva or pupa. T. officinale: Phanacis taraxaci

15b Galls gradually terminating, flat spindle-shaped, initially yellowish-green, later on reddened to dark brown, of very different size, 2‒7 (15) cm long; also on the sometimes strongly curved inflorescence stalks and main leaf venation; in case of abundant occurrence secondarily also disfiguring the leaf blade. With many, spores situated in and on the vascular bundles. T. officinale: Protomyces pachydermus

16a On inflorescence stalks => 17

16b On capitula. Receptacle of the externally often hardly disfigured flower head weakly swollen; containing a larva with conspicuous mandibles. T. officinale: Campiglossa producta

17a Swellings several mm long => 17

17b Single galls multicellular, only up to about 1 mm long, yellow- dark orange, sometimes additionally coalescing into disfigured, tubercular ridges or crusts. T. officinale: Synchytrium taraxaci

18a The inducer is situated inside the galls => 19

18b Spindle-shaped yellowish swellings bearing aecia. T. officinale: Puccinia dioicae

19a Galls locally confined, with tough, glabrous surface => 20

19b Galls without cavities, of different sizes and situations; spongy soft, yellowish-green, the surface ± undulately rugose; strongly curving the inflorescence stalk; also sometimes extending from the stem into the receptacle of the swollen and ± curved flower head. T. officinale: Ditylenchus dipsaci

20a Inflorescence stalk usually with many massive bulges over its complete length, spindle-shaped ± vitreous, yellow-green, which sometimes cause slight bending of the stem. T. officinale: Protomyces pachydermus

20b Base of inflorescence stalk slightly swollen over a length of several cm, close to the ground with several irregular humped protruding bulges, conspicuous when compared with unaffected shoots by their more compact structure. In the proliferated, more compact pith are 1‒2 (3) tunnelling larvae. T. officinale: Phytomyza wahlgreni

20c Localised tough-walled unilocular galls, 2–4 mm long, distinctly defined, pale green or also conspicuously reddened, often coalesced into much larger 25 mm long and 10 mm thick, ± tuberculate structures. Containing one white larva per chamber. T. officinale: Phanacis taraxaci

Last modified 26.iv.2020