Plant Parasites of Europe

leafminers, galls and fungi

gallers on Thymus

Dichotomous table for gallers on Thymus

by Hans Roskam

1a On parts above ground => 2

1b Roots with small swellings, nodule- to spindle-shaped. Thymus spp.:
Meloidogyne hapla

2a On inflorescences or flowers => 17

2b Malformations on vegetative parts, sometimes encroaching onto inflorescence => 3

3a On leaves, stems or terminally on single shoots => 4

3b Witches’ broom-like malformation of complete shoot systems caused by a perennial mycelium. Internodes abnormally elongated, erect, sometimes ± distorted; distal leaves diminished in size. Formation of flowers often aborted. Stem slightly thickened close to nodes, with brown telia. Thymus spp.: Puccinia thymi

4a Galls on axial parts, occasionally encroaching onto lateral organs => 14

4b Malformations on leaves, terminally on shoots without conspicuous swelling of the sometimes ± stunted internodes => 5

5a Terminally on shoots => 9

5b On leaves => 6

6a Causers occur inside galls => 8

6b Malformations covered with sori of fungi => 7

7 Rotund- to oblong-oval flat yellowish-brown bulges on ± curved midribs or stalks of leaves, sometimes on severely distorted stem parts with scattered or crowded sori, bearing ± circularly arranged aecia. Thymus spp.: Puccinia thymi-stipae

7b Black-brown, compact pads bearing telia on swollen, deflected petioles or sometimes almost circular distorted stems, rarely on leaf blades. Sori on inner side of distortions. T. fallax, fedtschenkoi, kotschyanus, serpyllum: Puccinia serpylli

8a Leaves disfigured, succulent; galls compact. Thymus spp.: Ditylenchus sp.

8b Elliptical, 2–2.5 mm long galls on underside of arched leaves; containing a single beetle larva. T. pulegioides & subsp. montanus, serpyllum: Squamapion serpyllicola

8c Leaf blades, especially on undersides, with many warts, occasionally joining, hardly 1 mm long, golden-yellow, later on browned, multi-cellular. Galls also on petioles and stems. T. pulegioides & subsp. chamaedrys, serpyllum: Synchytrium aureum

9a Accumulation of buds or rosette- to tuft-like clustering of leaves, flower primordia on severely stunted shoots or lateral buds => 10

9b Many leaves on ± shortened shoot tips rolled upwards- or inwards at margin; bearing colonies of deep dark-green aphids, about 1 mm long. Siphunculi black like the equally long cauda. Thymus spp.: Aphis serpylli

10a Galls with conspicuous pubescence => 13

10b Galls glabrous or weakly pubescent => 11

11a Causers occur inside galls => 12

11b Heavily infected shoot tips stunted, sometimes large parts reddened, ± disfigured as well as the inserted leaves. The causer, covered with a ± arched scale, lives on the outside of the malformations. T. pulegioides & subsp. chamaedrys, serpyllum: Rhizaspidiotus canariensis

12a Both apical leaf pairs amongst the terminal leaves, which are not involved in the gall formation, develop into a globular to oblong-oval gall up to about 4 mm long. Leaves shortened, swollen hemispherical to boat-shaped, thickened at base; outside glabrous, greenish-yellow or also conspicuously reddened. Between the pale inner leaf pair lives a yellowish-red larva. Thymus spp.: Janetiella thymi

12b Shoot tip with a tuft of reduced, disfigured, often vivid red coloured, sometimes slightly pubescent leaves or clustered abnormal flower buds. Thymus spp.: Aculus minor

13a Rotund or often bell- to barrel-shaped, ± rosette-like shoot consisting of shortened and broadened leaves, or stunted and disfigured, sometimes ± greened flower buds; occasionally with similarly disfigured, compact branchings. Leaves, especially on outside, strongly whitish and long pubescent. Terminally on vegetative or generative shoots, also on lateral buds. Thymus spp.: Aceria thomasi

13b Gall similar; many shortened and broadened, the exterior ones broad heart-shaped, inner ones becoming more slender. Abnormal pubescence restricted to inner leaf blades and marginal parts of leaf blades. Galls 5–10 (12) mm broad and up to 6–10 mm high. Terminally on shoots, smaller also on lateral buds. Containing single, rarely several red larvae. Thymus spp.: Bayeriola thymicola

14a Causers occur inside galls => 15

14b Stem locally swollen, spindle-shaped to irregularly bulging, often variously curved; with single or several walled depressions containing causer. Thymus spp.: Planchonia arabidis

= Regarding stem galls caused by rust fungi, see lead 7

15a Stem with rotund or oblong-oval swellings, up to about 4 mm long, containing a single larva => 16

15b Stem, especially at base, swollen over several internodes about double its normal girth. Leaves and lateral buds at infestation site stunted and swollen, especially the basal parts. Eelworms present in the broadened loose pith and rind parenchyma. Thymus spp.: Ditylenchus sp.

16a Usually upper part of stem, more rarely on a node, with swelling, up to 4 mm long and 2 mm thick, covered by the glabrous, not ruptured, rind. Containing a single yellow larva. T. praecox subsp. polytrichus, pulegioides, serpyllum, vulgaris: Squamapion atomarium

16b Stem with very small, one-sided, rotund swelling, up to 2 mm high, rupturing the rind. Containing a single larva. T. serpyllum: Squamapion atomarium

17a Malformation of single or several flowers; the vegetative organs usually remain unchanged => 19

17b Malformation includes flowers as well as other parts of inflorescence => 18

18a Primordia of inflorescence transformed into ± bud-like, conspicuously white pubescent tufts. Thymus spp.: Aceria thomasi

18b In stunted parts of inflorescence shortened, broadened and thickened, mussel-shaped arched, often conspicuously reddened bracts develop. A single yellow-red larva lives between bract and disfigured flower in a chamber-like cavity at base of never abnormally haired galls. Thymus spp.: Janetiella thymi

19a Flowers swollen, unopened. Galls not conspicuously haired; caused by gall midge larvae => 20

19b Flowers disfigured, with weak, abnormal pubescence. Calyx 2–3 times as large as normal. Corolla swollen, unopened, ± reddish. Stamens and ovaries leaf-like. T. serpyllum: cf. Aculus minor

20a Flowers severely disfigured => 21

20b Flower unopened; weakly swollen; calyx at base slightly thickened, about two or three times as large as normal, 2.5–3 mm long, broader than long, ± violet discoloured. Corolla as long as calyx, hardly visible. Stamens and ovaries aborted. Inner wall lined with mycelium. Containing a single red larva. Thymus spp.: Asphondylia serpylli

21a Flowers unopened, hardly recognisable, transformed into little gall. Inner wall lacking mycelium. Containing a yellowish-red larva. Thymus spp.: Janetiella thymi

21b Flowers unopened, completely disfigured, transformed into an oblong-oval gall. Calyx twice as large as normal, longer than broad; corolla enclosed. Stamens and ovaries aborted. Inner wall with mycelium. Containing a single red larva. Thymus spp.: Asphondylia serpylli

Last modified 30.iv.2020