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 flower s 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 s.lat.:. 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 s.lat.: 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 s.lat.: Phragmidium fragariae

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

mod 15.xii.2019