Plant Parasites of Europe

leafminers, galls and fungi

gallers on Galium

Dichotomous table for gallers on Galium

(incl. Asperula, Cruciata, Crucianella)

by Hans Roskam

1a On parts above ground => 2

1b Subterranean buds transformed into a brownish gall, up to 4 mm long, tapering to a short tip, sometimes single, sometimes several united into larger complexes. Containing a single whitish larva. G. mollugo: Ametrodiplosis auripes

2a Galls in inflorescence primordia, inflorescences, or single flowers, or, fruits => 57

2b Galls on vegetative organs => 3

3a Galls compact, on shoot tips, axillary buds; bud-like or tuft-like => 36

3b Axial parts of leaves with localised to extensive galls or malformations on many leaves, which are more densely accumulated on ± stunted stems, but not in tuft-like clusters => 4

4a Malformations involve either shoot parts and leaves simultaneously, or organs with localised sori of fungi, curled leaves, leaf rolls, erinea => 13

4b Gall formation confined to minor or extensive parts of stems; leaves usually not involved => 5

5a Malformations usually restricted to a part of internode, or a node, rarely larger than 10 mm => 7

5b Malformations variable in extent, usually over several internodes => 6

6a Basal shoot parts, especially on seedlings, severely stunted and spongy. Axial parts of older plants over ± expanded areas spongy thickened, sometimes distorted; galls on surface ± wrinkled; inserted leaves ± reduced and often with stalks and basal vein parts similarly swollen. G. aparine, verrucosum: Ditylenchus dipsaci

6b Several internodes usually swollen on all sides, with glabrous surface, constricted at nodes. Black sori developing in rind gleam lead-grey. G. mollugo, verum: Melanotaenium endogenum

7a Galls mostly of definite shape, caused by gall midge larvae => 8

7b Rotund-oval to elongate spindle-shaped, pale-green swellings, slightly protruding, on one side in various positions on internodes. Containing lighter spores. G. palustre: Physoderma vagans

8a Single galls smaller than 3 (4) mm => 9

8b One-chambered, rotund to oval swellings, about 4–10 mm long, fleshy-succulent to spongy, whitish or ± reddish especially on upper stem parts, also on inflorescences, often above a node; occasionally only overtopped by the final, distorted whorl of leaves. Often with several together and variously joined. At maturity ± star-shaped, rupturing with broad lobes. Aperture inside pubescent. Containing yellow to orange-coloured larvae. G. mollugo, sylvaticum, verum etc.: Geocrypta galii

9a Gall body ± enveloped by rind tissue, or protruding parts thin-walled => 11

=Some of following stem galls, reported for unidentified gall midges, might be confused with immature stages or galls of Geocrypta galii, disfigured by inquilines or parasitoids

9b Galls protrude distinctly from rind; wall fleshy => 10

10a Galls up to 5 mm across, situated below a node; often reddish marbled; – rupturing star-shaped. G. pumilum: cf. Geocrypta galii

10b Up to 3 (4) mm long, whitish fleshy galls with elongated conical top, usually situated close to shoot tip below the upper node; open laterally at maturity. G. anisophyllon, mollugo, pumilum, sylvaticum, verum, etc.: Dasineura sp.

11a Distinct swellings of epidermis => 12

11b bove the hardly swollen epidermis, and close to a node as on often curved internode, flat valve-like, up to 2 mm long and hollow, with nose-like elongation in the middle, inserted on small protruding pale socket, proliferations above an inconspicuous larval chamber. G. aristatum, mollugo, verum: Geocrypta rostriformis

12a On G. aparine: rotund to short spindle-shaped, one-chambered swellings situated above a node. Containing a single larva: Unidentified gall midge

12b Thin-walled gall on G. verum: below, or rarely above node, up to 2 mm long, yellowish, causing localised stunting, thickening and curving of the shoot axis: Unidentified gall midge

13a Stunting of axis associated with ± conspicuous accumulation of leaves; also erinea on various organs or curling, or rolling of leaves caused by animals => 23

13b Local, variously shaped swellings on shoot axis and leaves, caused by fungi => 14

14a Spores of fungi develop on surface of galled tissue => 16

14b Fruiting bodies develop inside gall => 15

15a Wart-shaped multicellular galls, up to 1 mm long, often arranged in rows or coalescing into crusts, almost only on lower, additionally little disfigured stem parts and on undersides of leaves. The warts consist of a strongly hypertrophied, slightly discoloured nutritive cell and similar auxiliary cells. G. mollugo: Synchytrium globosum

15b Similar multicellular, wart-shaped galls, associated with conspicuous additional malformations of infected organs. Belongs to the species complex of S. aureum. G. anisophyllon, boreale, palustre: Synchytrium galii

16a Malformations caused by rust fungi => 17

16b Malformations, according to extent of etiolation, running ahead, exhibiting elongated internodes and narrowed pale-green leaves, covered by down of branched conidiophores on underside. Assigned to facultatively disfiguring micro-species of the species complex. Asperula tinctoria, and with ± specialised micro-species on Galium: Peronospora calotheca species complex:

a On G. boreale, mollugo, palustre, saxatile, sylvaticum, uliginosum, verum: P. galii

b On G. aparine, spurium: P. aparines

c On Asperula purpurea: P. insubrica

17a Rust fungus develops several spore types during life cycle => 19

17b Fungus develops only telia, partially on pad-like swellings on leaves, partially on shoot axis on spindle-shaped, on one or all sides, rather conspicuous swelling => 18

18a Bulging, covered with black-brown spores, ± distorted swellings on stems and leaf axis or pad-shaped swellings on leaf blades. G. saxatile, pumilum: Puccinia lagerheimii

18b Malformations similar, spores lighter; germinated sori grey-brown. Cruciata laevipes, Galium mollugo, saxatile, sylvaticum etc.: Puccinia galii-verni

= From Arctic areas have been reported on leaves and stems of G. boreale: Puccinia rubefaciens

19a Fungus develops all spore types (one type may be absent) on same host => 20

19b On Galium only spermogonia and aecia of a host-alternating rust fungus develop. G. mollugo: Aecidium molluginis

= From G. boreale an isolated aecium has been described as Aecidium molluginis.

20a All spore types develop or spermogonia, and uredinia are absent => 21

20b Aecia absent. On Cruciata laevipes, paedemontana, etc.: Puccinia galii-cruciatae

20c Similar on G. scabrum: Puccinia galii-elliptici

21a All spore types present or only spermogonia absent. Also fungi with partially unstable succession of spore types, especially on respective secondary host => 22

21b Uredinia absent from life-cycle of this fungus which is distinguished by repeated development of aecia. Galls especially on stems and leaf veins. G. aparine, spurium: Puccinia difformis

22a Often all shoots of a plant stiffly extending, strange-looking, sterile. Leaves shortened, broadened, ± deflected; covered by densely arranged spermogonia and aecia, mainly on underside. Sori occasionally also on leaf upperside and stem. A. tinctoria, ciliata: Puccinia asperulina

22b Known from many Galium species, almost Cosmopolitan, developing all spore types on main host: Species complex of Puccinia punctata

23a Malformations on leaves, partially also occurring on stems, are associated with excessive pubescence or leaves have tight, narrow rolls of margin; caused by gall mites => 52

23b Malformations of leaf-bearing shoots, encroaching onto developing inflorescence, without additionally very dense pubescence or narrow roll of leaf margin, mainly caused by hemipterans, thrips or mites living on surface => 24

24a The very variable malformations bear aphids => 29

24b Malformations caused by other animals => 25

25a Malformations caused by psyllids, mites or spittlebugs => 26

25b The terminal, young leaves are variously rolled, twisted, distorted, discoloured and occasionally weakly bulging and thickened; Cruciata laevipes, Galium verum: Unidentified thrips

26a Malformations caused by psyllids or spittlebugs => 27

26b Plant completely or mainly of compact growth, lacking the typical thickenings of stem. The whorls of leaves deflected over the tip, mainly normally coloured and not excessively pubescent. Leaves are densely clustered on main shoots which may be excessively branched, giving the diseased shoot an truncated pyramidal outline. G. mollugo, verum: Inducer unidentified – ? gall mite

27a Malformations caused by psyllids => 28

27b The usually terminally infected shoot is stunted close to infestation and ± bent; the leaves inserted there are clustered and variously deflected and twisted. Infestation of generative shoots or inflorescences results in their stunting and to accumulation of all inserted parts: Philaenus spumarius

28a Cruciata laevipes. Longitudinal growth of several terminal internodes stunted. The stunted and slightly thickened stems bear accumulated shortened and broadened, inwardly curved, densely pubescent leaves. With several flat froth-covered nymphs: Unidentified psylli

28b On Galium and Asperula species. Leaves of clustered upper whorl thickened, margin ± strongly bent inwards or leaf blade disfigured, spoon-like. Often reddened and united to a rotund- to oblong-oval complex of galls. Trioza galii species complex. Note: key for adults:

a Galls on buds, stems and leaves of Galium, Rubia and Sherardia spp. Forewing membrane of adults lacking spinules except for the base of CU2. Trioza galii

b Similar malformations. Galium spp. Forewing membrane of adults with spinules present in all cells forming more or less extended fields: Trioza velutina

29a Aphids green to reddish or brownish => 31

= The aphid galls occurring on Galium are very variable, the causers are mainly oligo- to polyphagous. Identification only according to characters of the aphids.

29b Aphids dark-green to black => 30

30a Siphunculi often as long as, or slightly longer than cauda, at most only slightly shorter. Aphids usually only in small, stacked, balls of leaves, mainly on shoot tips, leaves distorted and ± twisted. G. aparine, spurium: Aphis fabae and/ or Aphis fabae subsp. solanella

30b Siphunculi of wingless aphids about a third as long as cauda. Leaves on stunted shoot tips ± clustered, roll-like; leaf blades distorted and twisted. Especially on G. mollugo: Aphis galiiscabri

31a Antennae longer than body => 33

31b Antennae about ¾ of body length or longer, at least reaching siphunculi => 32

32a Shoot stunted. Leaves of terminal shoots deflected. G. mollugo: Myzus persicae

32b The only slightly stunted shoots have loose whorls with deflected leaves. G. mollugo: Aulacorthum solani

33a Siphunculi slender, as long as, or longer than cauda => 34

33b Siphunculi of unwinged aphids short, thick and conical, shorter than cauda. Aphid pale greenish, yellow-brownish to dark ivory-coloured. Froth-covered nymph not red. Shoots terminally or inflorescences weakly stunted. Leaves of young whorl deflected. Asperula purpurea, G. mollugo, rubrum, verum: Staegeriella necopinata

34a Legs dark brown-black, siphunculi dark brown and about as long as the finger-shaped brown-black cauda. Aphid bicoloured with ± reddish thorax and olive-green abdome => 35

34b Siphunculi of unwinged aphids pale, at least twice as long as the triangular and also unpigmented cauda. Legs of apterae pale. Aphid 2 mm long, green to pale reddish. Shoots terminally severely stunted. The leaf tips are deflected in the terminally clustered whorls. G. mollugo, verum: Myzus langei

35a Shoots terminally stunted, whorl develops ± dense ball. G. austriacum, verum: Hydaphias molluginis

35b Shoot slightly stunted, with slightly deflected or occasionally not disfigured leaves. G. mollugo: Hydaphias molluginis

36a Galls develop from swellings of shoot tips or from swollen bases of densely clustered leaves, or they are shaped as ± loose tufts, which consist of a large number of ± transformed, not conspicuously haired leaves with freely ending leaf blades => 40

36b Galls consist only of leaves, which are bud-like or consist of almost closed structures; leaf blades are reduced or rudimentary => 37

37a Globular or oval galls, ± rounded at tip, up to 5 (6) mm, emerging from only a few whorls of leaves; midge galls => 38

37b Extensive bushy malformations, often appearing excessively branched, with strongly reduced leaves terminally on vegetative shoots or leafy generative shoots. G. mollugo, verum, etc.: Aculus anthobius

37c Galls up to 15 mm long and 8 mm broad, hollow, ± pubescent and stalked, roughly conical, or pear-shaped with beak-like appendage; many irregular proliferations inside with mites living in between. G. glaucum, mollugo, saxatile, verum, etc.: Aceria galiobia

38a More or less globular or egg-shaped galls containing yellow, non- jumping midge larvae at maturity => 39

38b Upper whorl clustered, tuft-like on severely stunted stem. Basal leaves broadened, disc-like ± discoloured, transformed into an artichoke- to bud-like gall up to 6 mm broad. Containing glossy, jumping, orange-red larvae. Asperula tinctoria: Contarinia asperulae

38c Shoot tip severely stunted. Axial parts and leaves swollen, spongy. All parts largely joined into a rotund gall, up to 6 mm long. Containing orange-red larvae. Asperula cynanchica, tinctoria, Crucianella angustifolia, Galium glaucum, odoratum, etc.: Dasineura asperulae

38d Egg-shaped, 2–4 (6) mm long gall, consisting of 2–3 whorls, usually terminally on side shoots, containing pale red larvae. G. mollugo: Dasineura sp.

38e Galls similar; often several joined into 10–15 mm long, ± barrel-shaped complexes. Each gall containing several larvae, pale orange-yellow at maturity, non-jumping. G. glaucum: Geocrypta sp.

38f Similar galls on G. boreale with 1–3 pale dirty-yellow larvae: Unidentified gall midge

38g Stem- or shoot galls on G. glaucum:

a Axial parts on tip of main- or side shoots severely stunted. leaves of several whorls densely clustered, shortened, especially the outer ones basally strongly broadened, slightly discoloured and with, contrary to the inner ones, only short, erect tips. Contain several pale orange-yellow, non-jumping larvae at base of 3–5 mm broad, rotund to cylindrical, sometimes slightly twisted malformations: Unidentified gall midge

b Axial parts with one-sided, 2–3 (4) mm long, laterally flattened, thin-walled proliferations of rind, the middle, usually yellowish-green part distinctly narrowed and crooked. Galls situated on internodes; on youngest shoots sometimes completely taking the severely stunted and at gall-free side convex curved internode. An oblong larval chamber containing a single pale to yolk-yellow, non-jumping larva: Dasineura sp.

39a Almost globular, often reddened galls, up to 4 mm long. The four leaves of the subapical whorl are greatly shortened and broadened, the severely disfigured, ± succulent, often calyx-like leaves enclose the whitish leaves of the inner whorl. Often containing several yellow larvae. G. palustre: Dasineura hygrophila

39b More or less elongated, nearly egg-shaped, 2–6 mm long galls, consisting of 2–3 whorls of imbricate shortened, broadened, spoon-like bent leaves. Often also on tips of shortened side shoots. Larvae yellow. G. pumilum, uliginosum, etc.: Dasineura sp.

40a Malformations caused by gall mites => 51

40b Malformations caused by gall midges => 41

41a Gall consists largely of fleshy swollen parts of shoot axis, or leaf base => 49

41b Tufts of leaves lacking conspicuous fleshy thickenings; leaf blades sometimes only thickened at base or ± completely broadened => 42

42a Large, loose, bouquet-like leaf tufts, up to 15 mm long. Larvae jumping, yellowish-white or orange-coloured, or red => 48

42b Similar or smaller leaf tufts. Larvae non-jumping => 43

43a Up to about 2 mm long, ± unopened leaf rosettes on G. mollugo and G. verum => 47

43b Larger rosette-like tufts with ± erect leaves => 44

44a On G. boreale or G. sylvaticum, resp. saxatile => 46

44b On G. pumilum, mollugo, verum => 45

45a On G. mollugo. Tuft consisting of 4–6 whorls, outer leaves usually distinctly broadened over their entire length, the inner ones only slightly changed. Containing several pale orange larvae: Dasineura sp.

45b On G. verum. Soft, broadened at base of leaf blades, usually crimson-red discoloured leaf rosette: Dasineura sp.

45c On G. pumilum: Dasineura sp.

46a On G. boreale. Loose tuft of leaves on shoot tip, often also in leaf axils. Outer leaves egg-shaped-oblong, inner ones shortened, egg-shaped: Unidentified gall midge

46b On G. sylvaticum. Outer leaves of tuft little changed, inside ones imbricate, increasingly reduced: Unidentified gall midge

46c On G. saxatile. Up to 8 mm long terminal tuft of leaves: Unidentified gall midge

47a About 2 mm long, from the upper whorl shaped rosette consisting of several shortened, thickened, white to red discoloured leaves. G. verum: Dasineura sp.

47b Similar gall on G. mollugo: Unidentified gall midge

48a On G. mollugo; large loose tuft of leaves. Outer leaves little changed, ± discoloured at base and thickened, the inner ones progressively reducing and covering one another. Containing dirty yellowish-white larvae: Contarinia molluginis

48b On same host live in largely similar galls, occasionally together with larvae of previous midge, the red larvae of Contarinia acrocecis

48c On G. verum. Oblong bouquet-shaped, up to 15 mm long tuft consisting of shortened leaves, or inflorescence primordia. Containing orange-coloured larvae: Contarinia sp.

48d On G. lucidum. Leaves terminally clustered, tuft-like, on the stunted shoot tips, shortened, ± spoon-like, converging. Also including inflorescence primordia; together making a 10–15 mm long gall. Between the organs live several larvae. Contarinia galii

49a More or less fleshy galls on G. aparine => 50

49b Artichoke-like, up to 8 mm thick, half open gall terminally on main- and side shoot, also on generative shoots. Leaves obliquely erect, shortened, broadened at base mussel-like, fleshy or cartilaginous, sometimes ± reddened or violet-tinged, later on browned. Containing several orange-yellow larvae: Dasineura galiicola

= In many aspects similar gall, but only 2–4 mm long, emerging from mussel-like broadened but not fleshy thickened leaf blade base on G. boreale, mollugo, saxatile, pumilum, scabrum, verum. Might be induced by an unidentified gall midge

50a Tuft pineapple-like, large, dense. Shoot axis severely stunted, spongy, swollen. Leaves at base succulent, whitish, abnormally pubescent, occasionally some leaves in the complex develop normally. Containing pale sulphur-yellow larvae. G. aparine, spurium: Dasineura aparines and/ or Macrolabis jaapi

= Both gall midges may occur together, but M. jaapi may cause the death of D. aparines. The first-reported species is frequent; the last-reported species might be an inquiline of the cecidogenic Dasineura and is moderately frequent

50b Similar gall formation. However, leaves lacking pubescence at base. G. aparine: Unidentified gall midge

51a A rotund gall consisting of clustered, inward curved leaves develops on tip of main- and side shoots. G. palustre: Unidentified gall mite

51b Several leaves on shoot tip curled/folded, bent inwards and united into a loose gall. Cruciata laevipes: Unidentified gall mite

52a Usually only the leaves are disfigured and are often abnormally pubescent => 53

52b Apart from pubescence mainly on underside and ± folded and distorted leaves, large parts of flowering or non-flowering stems are also ± abnormally pubescent. G. boreale: Cecidophyes calvus

53a The additionally pubescent, disfigured leaves are almost only terminally on shoots => 55

53b The similarly galled leaves also occur on lower inserted whorls as well as on shoot tips => 54

54a Roll of leaf margin, both upwards and downwards, often associated with twisting and bending of leaf blade. Depending on host characteristics with ± protruding abnormal pubescence: Cecidophyes rouhollahi and/or Cecidophyes galii

= Until recently, this gall has been recorded as being caused by C. galii, however recently the mite has been determined as C. rouhollahi. Galls of both mites are identical, hence, the identity of all galls must be verified by an expert. Because Cecidophyes rouhollahi has only rather recently been described all records of “galii” are unreliable; all British material probably belongs to rouhollahi.

54b On G. scabrum. Leaf blade spoon-like arched, margin partially rolled upwards: Unidentified gall mite

55a On G. saxatile or G. verum => 56

55b On Cruciata laevipes. Margin of leaf blade completely deflected upwards or rolled inwards; ± short, whitish to brownish, abnormal pubescence on upperside: Cecidophyes psilocranus

56a On G. verum. At shoot tip clusters of several whorls bear reduced, yellowish leaves, densely pubescent with short, white hairs: Unidentified gall mite

= Swellings and distortions of leaves on G. verum are caused by Aculus anthobius

56b On G. saxatile. Leaves rolled, pale-yellow or reddish, ± strongly pubescent leaves form densely clustered, gall on shoot tip about 3 mm long: Unidentified gall mite

57a On inflorescences or single flowers => 58

57b Single or several ovaries usually including neighbouring parts of stalk transformed into a sessile, often purple discoloured, rotund to oblong-oval sometimes hunch-backed gall with ± spongy wall. The galls, about 1.5–5 mm long, are crowned with single or several, ± reduced or normally shaped and coloured, but not spreading corolla leaves. Inner wall lacking mycelium. Each ovary containing a saturated orange or coral-red larva. Galls may sometimes look similar to those of previous midge. A. cynanchica, G. glaucum: Dasineura asperulae

57c Similar galls on G. glaucum contain several, later on pale orange larvae: Geocrypta sp.

57d Fruit enlarged. G. mollugo: Undescribed gall midge

58a Large parts of inflorescence are disfigured, or also with greening and leafiness of flowers => 59

58b The buds of single flowers are swollen, especially at base, up to 3.5 mm long, wall thickened, outside violet coloured, inside lined with mycelium. Containing a single, or occasionally 2 or 3 yellowish larvae. Asperula and Galium spp., Cruciata glabra, Rubia peregrina: Schizomyia galiorum

= Trotteria galii lives as an inquiline in galls of Schizomyia. – Galls with Trotteria are smaller and do not contain healthy Schizomyia-larvae – Trotteria larvae are reddish

59a Primordia of inflorescence completely disfigured or large parts of inflorescence stunted, also additionally branched, usually with several to many flowers greened or leafy => 60

59b Instead of flowers or fruits, ± conical or acuminated, pear-shaped galls with fleshy walls develop up to 15 x 8 mm, outside pale-green, inside bearing many irregular protrusions. Asperula cynanchica, Galium spp.: Aceria galiobia

59c Axial parts of inflorescences ± shortened, sometimes excessively branched. Flowers ± leafy, organs bent, sometimes pale-green to reddish especially apically. Asperula cynanchica, tinctoria, Galium glaucum, odoratum: Aculus minutus

= From GB (Scotland) on G. saxatile have been recorded condensed and purple unopened flowers caused by the eriophyid mite Aceria informis.

60a Malformations caused by midge larvae or mite => 62

60b Malformations caused by aphids => 61

61a Inflorescence stalks ± stunted to varied extent; flower peduncles shortened, flowers variously leafy. Occasionally with excessive branching and leafiness. Asperula and Galium spp., Cruciata laevipes, Rubia tinctorum: Aphis galiiscabri

61b Shoots and flower stems become deformed and stunted by aphids feeding in ant-attended colonies close to ground. Galium austriacum, lucidum subsp. fruticescens, mollugo, verum: Hydaphias molluginis

62a Malformations include greening or leafiness of flowers => 64

62b Malformations lack greening of flowers, and also lack abnormal pubescence => 63

63a Flower buds small, yellowish discoloured, unopened. In clusters on only slightly stunted shoots. G. verum: Unidentified gall mite

63b Primordia of inflorescence densely clustered, ball-like; transformed into a ± acute- or blunt conical gall, up to 10 (12) x 15 (20) mm, bearing lateral branchings and many small leaf tips at surface. Many red, jumping midge larvae live between organs. G. mollugo, verum: Contarinia acrocecis

= On G. mollugo in such galls occasionally live, together with the red acrocecis-larvae, the white larvae of Contarinia molluginis

64a Leafiness or greening without abnormal thickening of respective organs => 65

64b Flowers on stunted and ± excessively branched axial parts transformed into dense bunches of small, rolled, ± thickened leaves. G. palustre: Unidentified gall mite

65a Leafiness of ± clustered flowers on Cruciata laevipes, Galium pumilum, scabrum, sylvaticum: Unidentified gall mite

65b On many other Galium species a rosette of small leaves occurs instead of flowers, which are often ± clustered, ball-like, due to shortening of stalk: Aculus anthobius

= Tegoprionus dentatus, occasionally reported as gall causer on Galium, might be inquilinous in galls of Aceria galiobia, Aculus anthobius

Last modified 6.ix.2020