Dichotomous table for gallers on Geranium

by Hans Roskam

1a Galls on root collar or on parts above ground => 2

1b Roots with swellings only a few mm long, nodular or spindle-shaped, which bear side roots. Geranium spp.: Meloidogyne hapla

2a Malformations on inflorescences or flowers => 25

2b Malformations on vegetative parts => 3

3a Malformations caused by fungi, developing on surface or fruiting there => 17

3b Malformations caused by animals => 4

4a Gall formation includes single groups of organs or their parts => 5

4b Complete plant disfigured; basal stem parts variously swollen, spongy, from there developing organs ± reduced and disfigured. G. dissectum, molle: Ditylenchus dipsaci

5a Malformations on plant parts above ground => 6

5b Adventitious buds on root collar transformed into cauliflower-like proliferations, up to 20 mm long. G. molle, pusillum: Cause unknown – ? gall mite

5c Repeatedly reported leafy proliferations, have been attributed to Rhodococcus fascians

5d Closed fleshy proliferations, tuberculate at surface. Geranium spp.: Agrobacterium tumefaciens

6a Malformation of several organs on shoot tips or only on leaves => 7

6b Axial parts of shoot, also petioles, with bulging swellings with rimmed depressions containing the causer. Geranium spp.: Planchonia arabidis

7a Leaves with narrow rolls of margin or with strong pubescence => 10

7b Leaves lacking conspicuous pubescence; leaf blades deflected or loosely rolled, ± curled => 8

8a Malformations induced by aphids or spittlebugs => 9

8b Leaf blade ± curled, without particular curving. G. palustre, pratense: Unidentified hemipteran

9a Leaf blade strongly deflected, often ± nest-like, variously curled, dark green close to infestation. Geranium spp.: Philaenus spumarius

9b Several terminal leaf blades of shoots ± wrinkled and disfigured; tips loosely deflected or rolled. Shoot axis shortened if strongly infected, as well as stalks of clustered leaves. Geranium spp.: Acyrthosiphon malvae

10a Malformations distinguished by strong pubescence => 13

10b Narrow roll of leaf margin lacking conspicuous pubescence => 11

11a Malformation of many terminal leaves on shoots => 12

11b Leaflets often in single basal leaves, rarely in stem leaves, sack-shaped, rolled upwards, lighter. Veins thickened, containing several white larvae. G. sylvaticum: Unidentified gall midge

12a Leaf blade more subdivided, partially narrowly rolled inwards at margin. G. robertianum: Unidentified gall mite

12b Leaves on shortened shoot tip accumulated, tuft-like, tips rolled upwards, appearing almost needle-like, ± thickened, often reddened. Geranium spp.: Aceria geranii

13a Leaf blades with conspicuous rolls of margin => 14

13b Leaf blades with mainly yellow- or red discoloured irregular hunchbacked archings, covered with a white-silk-like glossy, abnormal pubescence. Hairs cylindrical, frizzy. Erinea may also encroach onto petioles, shoot axis and even calyx leaves. Geranium spp.: Aceria geranii

= The gall mite Aceria dissecti has been described from G. dissectum causing deformations of petals and young leaves, and shrivelling of leaves

13c Leaf margins hardly rolled inwards, more densely haired on both sides soon ± brownish discoloured. Mites free-living on leaf underside. G. caeruleatum, robertianum, sanguineum, sylvaticum: Epitrimerus geranii

14a Malformation of many clustered terminal leaves => 15

14b Malformations on shoot tips, of which axial parts, as well as petioles, are elongated and thinner. Leaflets rolled inwards and upwards, white erineum on underside. Inflorescences transformed into whitish capitula. Complete plant ± discoloured. G. molle: Unidentified gall mite

15a Leaves additionally subdivided due to infestation => 16

15b Shoot axis shortened, leaves accumulated, tuft-like, their tips rolled inwards and upwards, ± thickened, reddened, on many hosts conspicuously strongly pubescent. Geranium spp.: Aceria geranii

16a Shoot tip stunted, leaves ± finely subdivided, their tips ± rolled inwards, curved, twisted. Flowers ± distorted, accumulated into capitula, abnormally pubescent. G. pyrenaicum: Aceria schlechtendali

16b Similar malformations on G. dissectum, lucidum, molle, palustre, phaeum, sanguineum, sylvaticum: Aceria dolichosoma

17a Malformations bearing aecia and telia of rust fungi => 19

17b Malformations caused by mildew fungi => 18

18a Minor swelling, up to 1.5 mm long, situated mainly below the leaf blade on petiole, covered by at first white, then ± brown mycelium containing many punctiform perithecia. Geranium spp.: Podosphaera fugax

18b Grey-white down of conidiophores on leaf underside. Leaves usually completely diseased; at first developing faster, longer stalked than healthy ones; leaf blades smaller, yellowish-green, the margins usually loosely rolled downwards. Geranium spp.: Peronospora conglomerata

= The mildew Plasmopara wilsonii causes sharply delimited upper surface leaf spots on G. molle, phaeum, initially some mm large, ultimately often filling the entire leaf; pale yellowish at first, in the end violaceous brown

= Other Plasmopara species on G. palustre, pratense, sylvaticum and relatives occurring in similar down, are much more frequent, but are never cecidogenic

19a Malformations bearing spermogonia and aecia => 22

19b Swellings with only telia => 20

20a Teliospores 2-celled => 21

20b Teliospores 1-celled; on leaf underside in small, dark-brown dusty sori. G. phaeum, ? palustre: Uromyces carpathicus

21a Sori remaining covered by epidermis for a long period. Spores with compact stalks. Pads on leaf underside small, on yellowish to reddish discoloured spots, or sori on spindle-shaped variously distorted bulges on stems, petioles or main veins, up to 20 mm long, usually red to crimson margined. G. albiflorum, macrorrhizum, pratense, sylvaticum: Puccinia morthieri

21b Pads soon naked and powdery; spores easily falling, with warty surface. Sori in densely arranged groups on ± distinct, small or elongated, up to even 80 or more mm long, often variously distorted bulges. Geranium spp.: Puccinia geranii-silvatici

21c On similar malformations on G. macrorrhizum develops Puccinia flahaulti

22a Mature aecia often arched and wide open => 23

22b Mature aecia appearing depressed, with narrow ostiole, margin star-shaped, lacerate, soon falling. Sori on leaf underside on large, rotund, slightly swollen, tuberculate, reddened spots. G. sanguineum: Puccinia oerteliana

23a Aecia on conspicuously thickened pads. Fungi monoecious. Peridium cells only loosely connected. Often conspicuous swellings, often associated with strong distortion, yellowish, sometimes ± reddish margined, on main veins encroaching into the leaf blade, or bulges of variable length on petioles and stems. Geranium spp.: Uromyces geranii

23b Aecia on not thickened leaf sites, surrounded by distinctly discoloured areas. Minor swellings may develop facultatively if sori encroach onto main venation. Fungi host alternating => 24

24a Sori mainly on intensively blood-red or crimson discoloured spots, sometimes additionally surrounded by a yellowish-green area. Peridium cup-shaped with rigidly connected wall cells; after opening the margin finely frayed and bent inwards. Geranium spp.: Puccinia polygoni-amphibii

24b Similarly without intensive marginal discolouration spots develop on G. columbinum, dissectum, molle, pusillum, rotundifolium: Puccinia polygoni

25a On flowers or fruits => 27

25b Expanded parts of inflorescence disfigured => 26

26a Malformation by aphids; the distorted and abnormal pubescent flowers are clustered. Geranium spp.: Acyrthosiphon malvae

26b Flower head-like clustering of disfigured, ± abnormally pubescent flower buds or calyx leaves, caused by gall mites => 14

27a Flowers ± swollen, unopened. Geranium spp. Several unidentified gall midges

27b Fruit basally ± strongly swollen. Containing several orange-yellow midge larvae. G. sanguineum, sylvaticum: Dasineura geranii

mod 8.xii.2019