Dichotomous table for gallers on Tilia

by Hans Roskam

1a Galls on leaves, inflorescences or flowers => 7

1b Galls on axial parts such as twigs, branches and stems => 2

2a Galls on young shoots => 4

2b Malformations on stems or branches => 3

3a Rimmed wounds caused by cancers on branches, rarely on younger stems. “Nectria-cancer”. T. cordata, platyphyllos: cf. Neonectria ditissima

3b Older axial parts often with well-developed, oblong-spindle-shaped or compact oval swellings: Viscum album

4a Gall causers live outside the malformations => 6

4b Gall causers develop inside the galls => 5

5a Up to 8 mm wide swellings on all sides or one-sided, ± globular on the one-year old twigs. Inside is an expanded tunnel containing a caterpillar with distinct head capsule. Tilia spp.: Unidentified lepidopteran

5b Galls on young shoots ± globular to acuminated, barrel-shaped, succulent, up to 10 (20) mm across; at various locations, usually on suckers, especially the buds, which are often ± extensively involved in the gall formation. Each chamber containing a single sulphur- to lemon-yellow larva. Tilia spp.: Contarinia tiliarum

5c Plurilocular swellings on young shoots. T. cordata, platyphyllos: Contarinia ramicola

6a Axial parts of the younger shoots with slightly rimmed depressions containing a pear-shaped, 2.5–3 mm scale: Chionaspis salicis

6b Furthermore, with similar biology: Diaspidiotus gigas

6c Depressed gall-like grooves, occurring predominantly in branch axils. Tilia spp.: Xylococcus filiferus

6d Spring shoots terminally twisted. Leaves clustered nest-like, leaf blades rolled, curved and curled round each other. T. cordata, platyphyllos: Patchiella reaumuri

7a On inflorescences or flowers => 23

7b On leaves => 8

8a On developing, already unfolding or mature leaves => 9

8b The more or less developed young leaf blades terminally on stunted shoots remain irregularly crumpled and upwardly folded. Venation undulately disfigured, slightly thickened, sometimes more pubescent. The folds contain several at first white, then orange-yellow to reddish larvae. Tilia spp.: Dasineura thomasiana

9a Leaf blades browned, curled or with rolled margins and sometimes with abnormally felt-like pubescence, on the petioles and even extending onto the shoot => 16

9b Leaves with different, more or less constant localised galls => 10

10a Galls semiglobular, nodular or horn-like, always often with only narrow opening, towards the underside of the leaf => 13

10b Galls closed, ± globular to egg-shaped or flat pustule-shaped => 11

11a Galls irregular rotund to acuminate rotund-oval => 12

11b Leaf blade usually with several to sometimes many flat, circle-shaped parenchyma galls, hardly protruding on the upper side, on the underside slightly arched, pustule-shaped, sometimes reddish or yellowish brown rimmed. Containing a single white larva. Tilia spp.: Physemocecis hartigi

12a Galls dispersed on the leaf blade, often many per leaf; tough-walled, rotund, up to 8 mm wide and about 4 mm high; on one side arched-conical, on the other side rather bulging disc-shaped; predominantly protruding more on the upperside; often yellowish or reddish rimmed later on. From the conical part separates centrally at maturity an often differently coloured, brownish, cylindrical-conical, longitudinally grooved inner gall, containing a glossy white to pale yellow larva. Tilia spp.: Didymomyia tiliacea

12b Galls on petioles or veins; acuminated, rotund-oval, about 4–6 mm long, succulent, pale green; one-, more rarely more-chambers; each chamber containing a single sulphur- to lemon-yellow larva. Tilia spp.: Contarinia tiliarum

13a Galls nodule-shaped or wart-like => 14

13b Leaf blade on upperside with slender, about 5 up to even 10 (15) mm long horn-like, so called “nail galls”. Galls scattered on leaf blade, at first green, eventually yellowish, reddened or browned, glabrous or ± pubescent, acuminate, partially also rounded. Underside with narrow, pubescent opening; inner wall with loose, cylindrical pointed hairs of various length. Similar galls with rather host-specific mites:

a On T. cordata, platyphyllos, tomentosa: Eriophyes tiliae

b On T. argentea: Aculus argenteae

14a Galls at any place on the leaf blade => 15/p>

14b Leaf blade often with many almost semiglobular upward protrusions in the vein axils. Galls at first often strongly pubescent, eventually ± glabrous. Cavity open on underside and clothed often with prominent tufts of 1-celled, cylindrical, acuminate hairs. Tilia spp.: Eriophyes exilis

= In the vein axils of many woody plants occur hair formations, tuft-like, or arranged in rows, which may sometimes be even slightly bulged on the upperside of especially young leaves of lime trees. These “acarodomatia” or “mite pubs” may secondarily be inhabited by free-living mites, but are not true galls

15a Scattered nodular pouch galls; occurring on both sides of leaf; often many per leaf blade. Up to 3 mm long, up to 1.5 mm wide. Outside at first finely haired, eventually becoming glabrous, often with only some rigid hairs at base. Opening slit-like, densely pubescent. Cavity with tufts of simple hairs. T. platyphyllos: Phytoptus bursarius

15b Similar, flatter wart-shaped pouch galls, densely haired inside. T. cordata, platyphyllos: Phytoptus stenoporus

16a Leaves and additionally sometimes also the petioles with abnormal pubescence => 20

16b Leaf blades arched and curled or rolled at their margins => 17

16c Leaf blade browned. True gall? T. platyphyllos, cordata: Aculus ballei

17a Rolls of leaf margin => 18

17b Leaf blade variously ± irregular spoon- or trowel-like downwardly deflected, curled and locally coloured dark green. Tilia spp.: Philaenus spumarius

18a Roll in cross section larger than 2 mm; of varied length => 19

18b Roll narrow, compact, undulately-nodular thickening; ± pale green, usually rolled downward, occasionally upward. They often occur either with several per leaf blade and only a few mm long, or are sometimes coalescing and widely expanded. The inside is clothed with simple, pointed hairs. Tilia spp.: Phytoptus tetratrichus

19a Margin rolled upwards. Roll compact, succulent-cartilaginous thickening, brittle, wall almost glabrous, ± pubescent, yellow-green or often crimson- to violet red. Inside glabrous; often with several yellow-red larvae. Tilia spp.: Dasineura tiliae

19b Margin often on both sides of leaf with widely expanded, loose, not thickened, usually distantly-undulate upward roll. The leaf parenchyma is blotch-like mined inside the rolls up to both epidermises. Containing a single larva. Tilia spp.: Parna tenella

20a Erinea at various locations on the leaf blade => 22

20b Abnormal hair formations in the vein axils or along the venation => 21

21a Erinea flaky, white, sometimes slightly reddened, extending along the veins. On the upperside often coalescing at the branching of the veins; on the underside usually developed more sparsely. Tilia spp.: Eriophyes exilis and/or: Eriophyes nervalis

21b On the upper side in the vein axils almost semiglobular arched, haired protrusions, which eventually become glabrous. The cavities on the underside are often clothed with projecting dense tufts of 1-celled acuminate cylindrical, soon browned hairs. Tilia spp.: Eriophyes exilis

22a Densely pubescent erinea, situated between the veins, at first whitish to reddish to violet, finally brownish. Making oblong-oval patches on the upperside and/or underside, which may coalesce in various ways. Hairs cylindrical, at top often club-shaped, also bent or slightly twisted. T. cordata, platyphyllos: Eriophyes exilis

22b Similar erinea on the underside consisting of cylindrical hairs, rarely on upperside. Occur in distinctly margined, up to 5 mm, rotund- to oblong-oval patches which are clearly arched on the opposite side. T. tomentosa: Phytoptus erinotes

23a Bracts with horn-like, or felt-like galls or with rolled margins => 24

23b Globular or ± acuminated, oval, 5–8 mm, succulent swellings of flower buds, on midrib of the bracts or on the stalks of the inflorescence. Tilia spp.: Contarinia tiliarum

24a Leaf blades with erinea or horn-like- to nodular galls => 26

24b Leaf rolls => 25

25a Roll arched upward, succulent, brittle; often extending onto midrib; with uniform surface, glabrous or haired, often conspicuously reddened. Larvae yellow-red. Tilia spp.: Dasineura tiliae

25b Margin with narrow, leathery, undulate-nodular galls caused by mites These are pale green, up to 1 mm high, about 2–10 mm long, may coalesce into larger stripes, glabrous or haired rolls. Tilia spp.: Phytoptus tetratrichus

26a Leaf blades with erinea of various expansions. Erinea sometimes extending onto galls of other origin. Tilia spp.: Eriophyes exilis and/or: Eriophyes nervalis

26b Leaf blade with horn-like galls. Tilia spp.: Eriophyes tiliae

mod 30.iii.2020