Plant Parasites of Europe

leafminers, galls and fungi

gallers on Rhamnus

Dichotomous table for gallers on Rhamnus

by Hans Roskam

Incl. Frangula

1a Galls only on flowers or fruits => 23

1b Malformations on vegetative organs => 2

2a Buds thickened, not opening; or galls only on leaves => 15

2b On leaves, ± including shoot axis or on shoot axis and sometimes additionally on axis of inflorescence => 3

3a Malformation of several leaves terminally on young, ± stunted shoots, caused by aphids => 11

3b Witches’ broom -like malformations or localised galls on various parts => 4

4a Conspicuous, ± expanded thickenings and distortions caused by scale insects or rust fungi => 5

4b Buds on woody parts developing into several short shoots, which in turn develop many lateral buds, which are severely stunted. Witches’ broom-like malformations. R. cathartica: Unidentified gall mite

4c On Frangula alnus and Rhamnus cathartica have been reported: Viscum album

5a Galls caused by rust fungi => 6

5b Bark of young axial parts swollen, with rimmed depressions, each containing a flattened froth-covered nymph under a pear-shaped scale. Frangula alnus; Rhamnus alpina subsp. fallax: Chionaspis salicis

6a Young shoot axis with variously curved, yellowish swellings, up to several cm long. Similar, ± spindle-shaped smaller galls on petioles and leaf veins; ± rotund swellings on leaf underside, on calyx, greened flower parts or on young fruits. On R. alpina, pumila, saxatilis, also on cultivated introduced species => 7

6b Similar malformations on Frangula alnus; Rhamnus alaternus, alpina, cathartica, lycioides subsp. graeca, pumila, saxatilis; species-complex of Puccinia coronata

7a Swellings bearing aecia on R. alpina, pumila, saxatilis => 8

7b On Frangula alnus: Puccinia coronata

8a Aecia on R. alpina, pumila => 10

8b Aecia on R. saxatilis => 9

9a Fungus alternating with several grasses; telia apically with lateral or upwardly directed appendages; species-complex of Puccinia coronata

9b Fungus alternating with Sesleria albicans. Telia without appendages: Puccinia sesleriae

10a Aecia recorded on R. alpina in the Alps:

a uredinia, telia mainly on Calamagrostis varia: Puccinia alpinae-coronata

b uredinia, telia on Sesleria caerulea: Puccinia sesleriae-caeruleae

10b Aecia in alpine areas on R. pumila:

a uredinia, telia mainly on Calamagrostis varia: Puccinia alpinae-coronata

b uredinia, telia mainly on Sesleria caerulea: Puccinia sesleriae-caeruleae

11a Leaf blades of inconspicuously clustered terminal leaves rolled or conspicuously converging upwards => 13

11b The variously arched or deflected terminal leaves are clustered, nest-like => 12

12a Shoot tips stunted, Leaves loosely arched, ± slightly discoloured. Aphid 1.5 mm long, marbled dark-green. Siphunculi black, twice as long as the oblong cauda. Frangula alnus; Rhamnus alaternus, alpina, lycioides incl. subsp. oleoides: Aphis frangulae

12b eaves rolled backwards, making loose tufts. Aphid 1.5 mm long, greenish-grey. Siphunculi dark, at least at base and tip, twice as long as the short conical cauda. Antennae half the body length. Body laterally with conspicuous small tubercles. R. alpina, cathartica, saxatilis subsp. tinctoria: Aphis mammulata

13a Margins of leaves are loosely rolled downwards, ± bulging => 14

13b Leaves along the midrib and partially also the side veins folded upwards and margins ± strongly rolled. Underside of main venation conspicuously protruding. R. cathartica: Aphis commensalis

14a Mainly on R. cathartica and close relatives, on leaves, margin of which is loosely rolled backwards. Aphid pale green. R. alaternus, alnifolia, cathartica, davurica, imeritina, ludovici-salvatoris, lycioides: Aphis nasturtii

14b Mainly on Frangula alnus in slightly rolled leaves. Aphid marbled dark green. Frangula alnus; Rhamnus alaternus, cathartica, lycioides incl. subsp. oleoides: Aphis frangulae

15a Malformations on leaves => 16

15b Buds swollen. Frangula alnus: Unidentified gall midge

16a Leaf blade abnormally pubescent or margin sometimes with expanded, hardly swollen or with thick succulent folds or rolls => 21

16b Leaf blade with protrusions or lenticular parenchyma galls => 17

16c Small pit-like depressions on underside of leaf. R. alaternus: Trioza marginepunctata

= Two rare Psylla species also cause pit galls on leaves: Cacopsylla rhamnicola on R. alpina incl. subsp. fallax, cathartica, saxatilis and C. alaterni on R. alaternus.

17a Golden-yellow warts or parenchyma galls => 20

17b Protrusions on upper side => 18

18a Mainly on R. cathartica => 19

18b Mainly on R. alpina; corniculate or pouch-shaped protrusions, up to 5 mm long, pale coloured with exit hole on underside. R. alaternus, alpina, lycioides subsp. oleoides, pumila: Trioza kiefferi

19a Small dome-shaped protrusions. A depression on underside containing a flat froth-covered nymph. Also on R. pallasii: Trioza rhamni

19b Protrusions small, ± pinhead-shaped: Aceria rhamni

= On Rhamnus alpinus and Frangula alnus the gall mite Calepitrimerus rhamni causes small finger galls on the upper surface of leaves

20a Underside of basal leaves with many warts, sometimes joining, multi-cellular, ± golden-yellow, less than 1 mm long. Frangula alnus: Synchytrium aureum

20b Inconspicuous parenchyma galls, up to about 5 mm broad, rotund, pale green, protruding and flattened on both sides, soon narrowed towards margins. Manifest as brown spots after departure of larvae. Each containing a single larva. R. cathartica: Unidentified gall midge

21a Underside of leaf with abnormal pubescence => 22

21b Leaf margin curved upwards over a length of 10–20 mm, more rarely rolled. Strongly succulent-cartilaginously thickened; often with abnormal pubescence. in the peripheral, not thickened parts. Rhamnus cathartica, ? Frangula alnus; Rhamnus alpina, erythroxylon, saxatilis: Trichochermes walkeri

21c ne to two pairs of terminal leaves conspicuously folded, often over their complete length, along the midrib and side veins and from margin to the middle part of leaf, or more rolled inwards and upwards. Containing many grey- to blackish-green aphids. R. cathartica: Aphis commensalis

22a Felt-like grey-green pubescence on underside, often emerging from veins. Hairs simple, thread-like or weakly club-shaped. R. alaternus, cathartica: Aequsomatus annulatus

22b Reddish erinea on underside; hairs multi-cellular, acute or obtuse. Frangula alnus: Unidentified gall mite

22c Vein axil along midrib ± discoloured. Abnormal white pubescence on underside in axils and on vein between axils. Frangula alnus: Unidentified gall mite

23a Flower galls => 24

23b Fruit weakly swollen and disfigured. R. cathartica: Wachtliella krumbholzi

24a Flowers swollen, unopened. Stamens and pistil aborted. Containing several whitish, later on sulphur yellow jumping larvae. Frangula alnus; Rhamnus pallasii: Contarinia rhamni

24b Similar galls with reddish-yellow, non-jumping larvae. Frangula alnus: Dasineura frangulae

= May not be independent gall causer, but inquiline in galls of previous midge.

24c Flower buds swollen, club-shaped, calyx green with ash-coloured pubescence, with reddish longitudinal ridges and distal part. Mature gall 5–6 mm long, 2 mm in diameter, coloured brownish when dried. Containing a single white larva. R. alaternus, ludovici-salvatoris: Asphondylia borzi

Last modified 30.iv.2020