Dichotomous table for gallers on Viola

by Hans Roskam

1a On parts above ground => 2

1b Roots with nodular or spindle-shaped swellings. Viola spp.: Meloidogyne hapla

2a On flowers or capsules => 26

2b On vegetative parts => 3

3a On buds, leaves, shoot tips or stems => 4

3b Complete plant disfigured. Buds in spring swollen ± globular, up to 10 mm across, pale-green; later on developing into cauliflower-like structures, up to walnut-size, which consist of strongly shortened, thickened, often ± adnate leaf-, runner- and flowering shoots and are sometimes overtopped by severely disfigured, discoloured organs. V. odorata: Aphelenchoides fragariae

3c Often associated with previous eelworm: Rhodococcus fascians

4a On leaves and stems => 7

4b On buds or distinctly shortened shoot tips => 5

5a On shoot tips => 6

5b Terminal or lateral buds disfigured. Viola spp.: cf. Dasineura affinis

6a Terminal internodes distinctly shortened. Leaves as well as flower buds densely clustered, tuft-like; transformed into irregular, abnormally pubescent balls. Leaf blades and stipules rolled upwards, thickened; flower buds often sessile, disfigured; calyx and corolla often enlarged and twisted. Containing several pale orange-yellow larvae. V. arvensis, cornuta, calaminaria, elegantula, tricolor, subspecies and forms: Dasineura violae

6b Leaves on shoot tips densely clustered, rosette- to tuft-like, partially rolled, distorted, also strongly lobed; the outer ones glabrous, the inner ones weakly pubescent. Larvae yellow-red, at maturity red, with weak ability to jump. V. arvensis, cornuta, tricolor: Prodiplosis violicola

6c Leaves with enlarged stipules clustered in the rosettes or on shoot tips. Leaf blades often rolled loosely upwards up to midrib, fleshy thickened, brittle. Rolls yellowish-green, glabrous or sometimes densely haired on pubescent species, hiding flower primordia; calyx and ± greened corolla disfigured, enlarged and thickened. Containing several, at first white, later on orange larvae. V. calcarata, canina, elatior, hirta, palustris, reichenbachiana, riviniana: Dasineura affinis

7a Swellings bulge-like, often more than 5 mm long or even widely expanded; on stems, runners, petioles or leaf blades. Galls caused by rust- or smut fungi => 22

7b Other malformations, mainly on leaves => 8

8a Leaf blades rolled or curled, caused by animals => 14

8b Galls less than 1 mm long, wart-shaped, or leaf blades with ± expanded bladder-shaped swellings. Galls induced by fungi => 9

9a Leaf blades swollen, bladder-shaped. Fungi fruiting at surface => 13

9b Leaf blades, mainly on underside, often with many wart-shaped galls. Galls also on petioles and basal stem parts. Fruiting bodies inside galls => 10

10a Content of nutritive cells red-yellow or yellow. Warts compound => 12

10b Nutritive cells with inconspicuously coloured content => 11

11a Warts mainly simple, flat, slightly protruding, single or later on coalescing into browned crusts. V. biflora: Synchytrium alpinum

11b Warts compound, distinct, mainly ± hemispherical; single or on crusts. V. canina, erecta, odorata, pumila, reichenbachiana, riviniana stagnina: Synchytrium globosum

12a Galls consisting of many cells; protruding as ± hemispherical warts; sometimes coalescing crust- or ridge-like and causing additional malformations. V. canina, erecta, odorata, pumila, reichenbachiana, riviniana stagnina: Synchytrium globosum

12b Galls consist of only a few cells, only slightly arched. V. biflora: Synchytrium saxifragae

13a Leaf blade with smaller to expanded archings, bladder-like, pale-green, slightly thickened. Petiole and stem often with elongate, ± distorted, bulges. Galls bearing honey-yellow spermogonia and many yellow aecia. Viola spp.: Puccinia violae

13b Only a few upward arched, slightly thickened, pale-green, sometimes violet margined, rotund to elongated elevations on leaves of many pansies; largely diseased leaf parts at margin often ± upwardly, deflected at tip. Infestation covered with a violet tinged down on underside. On many pansies, also on V. arvensis, biflora, calcarata, cornuta, riviniana, tricolor, x wittrockiana: Peronospora violae

14a Leaves variously curled, also partially with irregularly thickened folds or rolls of margin caused by aphids, spittlebugs or mites => 17

14b Leaf blades with rolled margins caused by gall mites or midge larvae => 15

15a Leaf margin loosely rolled upwards. Gall wall slightly bulging to fleshy thickened. Midge galls => 16

15b Leaf margins very narrowly rolled upwards. Rolls usually not thickened and discoloured, often only on basal part of margin. Leaf blade often variously distorted. If strongly infected, all leaves of the etiolated plant are sometimes completely disfigured. Viola spp.: Cecidophyes violae

15c On V. biflora in similar usually abnormally white pubescent galls, lives the heteromorphic in adult stage: Coptophylla borealis

16a On V. hirta. Margins often of both leaf halves rolled over up to midrib along almost complete length or on older leaves only rolled upwards in basal half. Gall wall slightly thickened, mainly, occasionally in middle part of roll, ± yellowish green. Containing several at first white, later on orange-red larvae: Dasineura violahirtae

16b On V. odorata. Similar leaf rolls: Dasineura odoratae

16c Complete leaf margin, or especially the base, often with both sides rolled upwards, bulging. Roll thickened, brittle, often pale green, glabrous or, on pubescent hosts, sometimes more densely whitish pubescent. Containing several at first white, later on orange-yellow larvae. V. calcarata, canina, elatior, hirta, palustris, reichenbachiana, riviniana: Dasineura affinis

17a Malformations caused by aphids => 19

17b Malformations caused by spittlebugs or mites => 18

18a Leaf blade over tip and margins ± spoon-shaped, deflected and converged, curled or rolled, locally deep green. Sometimes several leaves on the ± stunted stem parts are clustered and similarly disfigured. Viola spp.: Philaenus spumarius

18b Leaf blade slightly curled, margins with broad, weakly pubescent upward roll. Viola spp.: Unidentified gall mite

19a Aphids basally brownish to yellowish => 21

19b Aphids yellowish or greenish coloured => 20

20a Margins of slightly curled leaves rolled upwards. Antennae of aphids distinctly shorter than body. V. odorata, reichenbachiana, tricolor: Myzus ornatus

20b Leaf margin rolled downwards, ± curled. Antennae longer than body. V. arvensis, hirta, mirabilis, odorata, palustris, reichenbachiana, tricolor: Aphis violae

21a Body of aphid usually brown; often in large colonies on host, leaves of which are rolled upwards. Flower peduncles shortened, flowers clustered. V. tricolor and subspecies, V. arvensis, mirabilis, reichenbachiana, tricolor: Myzus certus

21b Aphid pale- to grey-brown or yellowish. Leaves rolled, curled and clustered. V. arvensis, odorata, tricolor: Myzus ascalonicus

22a Malformations unopened or lead-grey, black dusted bulges after rupturing => 24

22b Swellings covered by yellowish aecia or brownish telia => 23

23a Swellings bearing cup-shaped aecia, often accompanied by spermogonia, in more dense groups on often bladder-like or bulging, sometimes distorted, yellowish pads of variable size, even measuring several cm long, occurring on all green plant parts. Fungus living on many violets, much more rare on pansies: Puccinia violae

23b Leaf-, also flower peduncles, with ± distinctly protruding, elongate, sometimes distorted, minor bulges caused by mycelia developing, chestnut- or chocolate-brown telia which long remain covered. V. epipsila, langsdorffii, macloskeyi, palustris, nephrophylla, selkirkii, stagnina: Puccinia fergussonii

24a Bulges on all green parts; at first lead-grey, then rupturing and with black dusting => 25

24b Lower stem parts ± shortened, swollen and curved. V. tricolor, arvensis, x wittrockiana: Ditylenchus dipsaci

25a Stem, runners, petioles, leaf veins and leaf blades or flower peduncles as well as even calyx leaves and ovary with conspicuous, ± expanded, often distorted bulge-like swellings. Bulges at first lead-grey, then rupturing and with dusting of black spore balls. Viola spp.: Urocystis violae

25b Similar, often expanded swellings, sometimes on all sides of stems, flower peduncles and leaves. V. arvensis, kitaibeliana, occulta, tricolor incl. subsp. macedonica: Urocystis kmetiana

26a Malformations on flowers => 27

26b Ovary swollen. V. tricolor and subspecies: Inducer unknown

27a Flower buds swollen on ± shortened shoots, disfigured and unopened. Containing midge larvae => 28

27b Receptacle swollen, often also neighbouring stalk as well as ovary. All infected parts thickened, disfigured and with at first translucent spore masses, later on filled with, blackish dusting. V. arvensis, kitaibeliana, occulta, tricolor incl. subsp. macedonica: Urocystis kmetiana

28a On V. calcarata, canina, elatior, hirta, palustris, reichenbachiana, riviniana: Dasineura affinis

28b On V. arvensis, cornuta, calaminaria, elegantula, tricolor, subspecies and forms. Dasineura violae

mod 13.xii.2019