Plant Parasites of Europe

leafminers, galls and fungi

gallers on genus Lactuca

Dichotomous table for gallers on Lactuca

(incl. Cicerbita, Mulgedium, Mycelis)

by Hans Roskam

1a On above-ground parts => 2

1b Mostly terminal parts of root with nodular swellings. L. perennis, sativa, serriola: Meloidogyne hapla

2a Malformations of inflorescences or capitula => 11

2b Galls on shoots or leaves => 3

3a Malformations almost exclusively on leaves => 6

3b Malformations on stems, with or without involvement of leaves => 4

4a Localised galls on shoots => 5

4b The overwintering mycelium causes a systemic infection, largely deforming the plant and inhibiting the formation of flowers. Internodes lanky, often excessively elongated, diseased stems ± prostrate; affected leaves pale green, shortened and on the underside, like the stems, with spermogonia and isolated aecia on expanded areas. Lactuca sibirica, Mulgedium tataricum: Puccinia minussensis

5a Shoots with spindle-shaped to oval or elongated bulges, with single to many depressions containing the gall causer. L. serriola, viminea: Planchonia arabidis

5b Conspicuous stem galls, about 30–45 mm long, 10–20 wide tuber- to spindle-shaped, tough. L. saligna, viminea: Timaspis phoenixopodos

6a Malformations mainly of the leaf blades => 8

6b Galls exclusively or preferentially on the petiole or on the midrib => 7

7a Conspicuous swelling of the midrib of basal leaves, especially protruding on the underside, glabrous on the surface, broad at the base, gradually narrowing, usually extending into the upper third of the leaf blade. Containing a single larva. L. serriola: Phytomyza penicilla

7b Spongy, ± spindle-shaped swellings of the midrib in different sites and of various expansion. Surface mostly rugose, inside massive. Occasionally extending into the leaf blade, which is often swollen and disfigured. L. serriola: Ditylenchus dipsaci

7c Midrib of leaf over a length of 8–15 mm swollen, blister-like and slightly bent; on the underside with dense rows of aecia and pycnidia, which may also appear scattered on the upper side. L. alpina, aurea, macrophylla: Puccinia mulgedii

8a Local, ± conspicuous swellings on the leaves caused by rust fungi => 10

8b Expanded malformations of the leaf blade => 9

9a Compact, narrow upward roll of the leaf margin. L. perennis: Unidentified gall mite

9b Leaf blade ± curled and discoloured. L. sativa, serriola: Nasonovia ribisnigri

= Sometimes occurring together with the aphid Aulacorthum solani

10a Leaf blade with 5–10 (15) mm long rotund, pale green to reddish spots, usually on the underside with a vivid yellowish hardly swollen pad bearing cup-shaped aecia; with a corresponding depression on the upper side. L. perennis, quercina, sativa, serriola, virosa, etc.: Puccinia opizii

10b Aecia with pore-shaped opening, unlike the cup-shaped opening of the preceding species, the peridium very loose, rudimentary. Sori on the underside of the leaves, on the leaf blades usually rather small and little swollen; on the venation, petioles and stems united in larger groups on bulge-like swellings. L. perennis, serriola, rarer on L. perennis, quercina, sativa, serriola, viminea: Puccinia lactucarum

10c On L. viminea with similar aecia to the preceding species: Puccinia maculosa

11a Stalks of young inflorescences or the basal parts of older inflorescences markedly stunted in longitudinal direction; ± thickened; budding inflorescences in various numbers at their base ± globular or mostly obtuse cone-shaped swollen; not opening. On later infected inflorescences the stalks are less stunted; finally only some to many disfigured capitula are distributed over the inflorescences. Containing many white, jumping larvae. L. serriola: Contarinia cf. salatica

11b Capitula often completely transformed into small tufts of irregular, curved leaflets. L. saligna, sativa, serriola, virosa: Aculus lactucae

11c Flower head remaining closed, swollen and longitudinal-ovoid. L. viminea: Hypenidium graecum

Last modified 18.xi.2023