Plant Parasites of Europe

leafminers, galls and fungi

gallers on Potentilla

Dichotomous table for gallers on Potentilla

by Hans Roskam

(incl. Argentina anserina, Drymocallis rupestris)

1a On above-ground parts => 2

1b Root collar, also root- or shoot parts close to surface with rotund galls, up to 5 mm across, single to multi-chambered, sometimes coalesced into conspicuous, tuberculate complexes of various extent. Each oval tough-walled chamber, about 2.5 mm across, containing a single larva. Potentilla spp.: Xestophanes potentillae

1c Nodular swellings without chambers on roots of Argentina anserina: Meloidogyne hapla

2a Galls conspicuous => 8

2b Extended erinea or very small, sometimes coalescing pustules or warts on all above-ground parts => 3

3a Leaf blades, -stalks and stems with small wart-like galls => 4

3b Erinea especially on the underside of sometimes hardly unfolded leaves, also on petioles, on stems and even on calyx. Hairs acuminate-cylindrical. Potentilla spp.: Phyllocoptes parvulus

4a Content of galls and warts yellow-red or pale coloured => 6

4b Content of galls colourless or warts dull-brown to black => 5

4c Underside of the leaves with a greyish white fungal bloom, consisting of erect, distally several times dichotomously branched conidiophores, each one ending in a conidium that is wider than long. P. chrysantha, supina incl.subsp. paradoxa, thuringiaca; also on Aphanes microcarpa: Peronospora oblatispora

5a Warts usually in groups, with colourless content. P. reptans: Synchytrium globosum

5b Pustules dull-brown to black; sometimes coalesced at curved infestation sites to ± expanded bulges. Argentina anserina; Potentilla reptans: Physoderma vagans

6a Warts clearly delineated; hemispherical to short-cylindrical arched => 7

6b Warts simple. P. argentea, heptaphylla: Synchytrium potentillae

7a Warts glabrous. P. reptans: Synchytrium aureum

7b Many (20–40) epidermis cells develop into strongly arched long, acute, white hairs. Plants conspicuously stunted if strongly infected. P. erecta: Synchytrium pilificum

8a On vegetative plant parts => 11

8b On inflorescences or flowers => 9

9a Galls caused by midge larvae or mites living inside flowers => 10

9b Apical shoots, possibly including inflorescences, disfigured, ± clustered, tuft-like. Potentilla spp.: Philaenus spumarius

10a Flowers unopened, abnormally pubescent. Calyx leaves ± elongated, stalk shortened, resulting in ± hidden flowers. Larvae many, orange-yellow to red. P. argentea, inclinata: Dasineura potentillae

10b Calyx of diseased flowers unchanged. Corolla and stamens etiolated, in P. norvegica ± greened. Receptacle elongated, with many stalked fruit primordia. The oblong, or more rotund bundle of young ovaries, if protruding from the flowers are long haired and bear long, ± curved styles. P. argentea, norvegica: Unidentified gall mite

11a Local, also ± expanded, galls on shoot stems, and on the stems of tillers, sometimes also additionally or exceptionally on petiole and even on midrib => 19

11b Malformations on leaf blades or on several disfigured leaves, mainly at, or close to, the shoot tip => 12

11c Small leaf rosette. P. grandiflora, pusilla, tabernaemontani: Guignonia potentillae

= From western Turkey on P. recta leaf bud galls have been reported which are caused by the gall midge Janetiella potentillogemmae. Several larvae live together; subsequent development of galls on lateral buds prevents the formation of side shoots with new inflorescence

12a Predominantly on single, not clustered leaves => 15

12b Mainly on clustered leaves => 13

13a Malformations caused by aphids or spittlebugs => 14

13b Leaves clustered at shoot tip, strongly pubescent. Larvae reddish. P. incana: Unidentified gall midge

13c Middle part of plant transformed into a rosette directly attached to rhizome. The rosette consists of many, 10–15 mm long, usually pale green, linear to lanceolate leaf-like structures. Between the inner linear leaves, still 5–6 mm long and with pale base, a single larva, spinning a snow white cocoon. P. tabernaemontani: Unidentified gall midge

14a Leaves, and also sometimes disfigured flowers ± clustered at the shoot tips. Leaf blades crumpled, deflected, locally intense green. Potentilla Philaenus spumarius

14b Branches and flower peduncles curved. Leaves variously disfigured. Argentina anserina; Potentilla erecta, reptans: Aphis tormentillae

15a Leaves curved, curled, folded or swollen, bladder-like => 16

15b Leaf blade with yellowish pustules. Drymocallis rupestris: Unidentified psyllid

16a Leaves rolled, folded or ± crumpled and curved => 17

16b Leaf blades with fleshy swollen spots or buckled and bladder-like to greater extent. Galls ± pale-green, on underside or both sides and soon covered with a dirty-grey layer of club-shaped, 8-spored asci. Infestation occasionally also on leaf midrib, -stalk or stem, which are swollen, and sometimes also elongated and ± bent. Drymocallis rupestris; Potentilla anglica, erecta, recta, x suberecta: Taphrina potentillae

17a Malformations without conspicuous pubescence => 18

17b Leaf blade contracted, curled, with stronger pubescence. P. argentea: Unidentified gall mite

18a Leaf midrib strongly deflected. Leaf blade at infestation site crumpled and sometimes deep-green, clustered. Potentilla Philaenus spumarius

18b Leaf midrib stunted, ± bent. Leaflets, ± rolled inwards, containing aphids. Argentina anserina: Unidentified aphid

18c Leaf blade rolled or folded at margin, curved, no abnormal pubescence. Argentina anserina; Potentilla crantzii: Cecidophyes potentillae

19a Galls closed, causers inside the tissue or in distinct chambers => 23

19b Galls open, causers living on surface or fruiting there => 20

20a Malformations contain fungus spores => 21

20b Petioles, also shoot axis, with cylindrical, ± discoloured yellowish, ± buckled swellings, often associated with bending; occasionally several scales solitary in irregularly rimmed depressions on same organ. P. argentea, erecta, grandiflora, hirta, recta: Planchonia arabidis

21a Leaf veins or -stalks with oblong, facultatively sometimes slightly swollen, yellowish spermogonia and orange-coloured caeoma-like aecia bearing pads. [Caeoma is an aecium in which the spores are formed in chains and not enclosed in a peridium]. Fungus monoecious, morphologically distinguished by its telia. Stalk of telia distinctly contrasting. 2–4 germ pores per cell, often situated in the middle or the side-walls => 22

21b Instead of caeoma-like aecia patches, with stalked, solitary primary uredinia. Stalks of telia indistinctly contrasted. Germ pores not apical. Teliospores 2–7 celled, each cell with a single germ pore. Rotund, developing sometimes reddened, with yellow spores occupying small swellings on leaf upperside. P. anglica, argentea, aurea subsp. chrysocraspeda, erecta, x mixta, recta, reptans: Frommeëlla tormentillae

22a Teliospores mainly 4-celled, rounded at apex, papilla absent. Aecia and uredinia with dense, broad warts. Potentilla Phragmidium fragariae

22b Teliospores 5–6 celled, with weak papilla. Aecia and uredinia with fine, loosely arranged warts. Potentilla Phragmidium potentillae

23a Malformations caused by animal inducers => 24

23b Small pustules or bulges on runners, petioles and also leaves. Strongly infected organs often etiolated or distorted. Argentina anserina; Potentilla reptans: Physoderma vagans

24a The inducers occur in larval chambers => 25

24b Soft, compact, spongy galls on the stems of Argentina anserina: Ditylenchus dipsaci

25a Chambers with tough, ± lignified wall => 26

25b Stems with small, rotund, one-sided swellings. Containing a single gall midge larva. P. erecta: Unidentified gall midge

26a Galls at least partially single, ± globular, ± coalesced into larger complexes => 27

26b Swelling spindle-shaped, about 10–30 mm long and 7–15 mm thick, mainly many-chambered and accordingly irregular tuberculate; especially on terminal parts of shoot axis. Each chamber containing a single larva. P. argentea, grandiflora, heptaphylla, inclinata, supina, wimanniana: Diastrophus mayri

27a Single galls about 2–3 mm long => 28

27b Axis of tiller, and more rarely the petiole, with rotund, one-chambered swellings, up to 6 mm thick; sometimes arranged like string of beads or mainly at first slightly bumpy, many-chambered, united groups up to 35 (80) mm long ± fused. Later on the rind bursts open and the single galls emerge more distinctly. Each chamber containing a single larva. Potentilla spp.: Xestophanes potentillae

28a Shoot axis, petiole and midrib with thin-walled, oblong-oval swellings, up to 3 (4) mm long, one-chambered; galls sometimes arranged in rows or groups Potentilla spp.: Xestophanes potentillae

28b Initially green, then brown, about 2 mm long, rotund swellings. One-chambered, mainly solitary or occasionally arranged in groups of various size; single galls however remain distinct and are hardly coalesced. Often close to ground, ± hidden in vegetation, sometimes solitary on petiole. P. anglica, erecta, grandiflora, heptaphylla, incana, inclinata. tabernaemontani: Xestophanes brevitarsis

Last modified 15.iii.2022