Dichotomous table for gallers on Epilobium and Chamerion

by Hans Roskam

1a Malformations on inflorescences, flowers or fruits => 23

1b Malformations on vegetative parts => 2

2a Malformations by fungi fruiting on surface, or many galls less than 1 mm long => 16

2b Malformations caused by animal parasites => 3

3a Malformations contain aphids => 13

3b Malformations caused by other causers => 4

4a Malformations localised or confined to only a few plant parts => 5

4b Complete plant severely stunted, largely disfigured. Axial parts ± swollen. E. palustre: Ditylenchus dipsaci

5a Mainly or only on leaves => 9

5b On stems => 6

6a Rotund to spindle-shaped stem galls, which contain causer => 7

6b Stem ± stunted and swollen; ± rotund-oval rimmed depressions on surface which contain causer. E. palustre, roseum: Planchonia arabidis

7a Galls conspicuous, ± barrel- to spindle-shaped, on nodes or internodes, mainly in the middle of stem parts => 8

7b Terminal part of shoot axis stunted, with slender swelling close above a node, 10–15 (30) mm long, often reddened. Pith contains a yellowish- to red-brown, brown-headed caterpillar. Chamerion angustifolium: Mompha sturnipennella

7c Lateral branches disfigured, usually just below inflorescences. E. hirsutum: Mompha bradleyi

8a Stem, usually above a node, with compact swelling, usually one-sided, acuminated, rotund- to oblong-oval, 6–15 mm long and 3‒5 mm thick, often reddened. Containing a white beetle larva. Chamerion angustifolium, much rarer on E. hirsutum, montanum: Auleutes epilobii

8b Stem with oblong-oval to elongated spindle-shaped gall, 6–8 mm broad, tough-walled, usually thickest at the node and ± gradually narrowing into the shortened internode. Galls often distinguished by a locally appearing, white web. An elongated tunnel in pith contains a grey-green, eventually reddish, black-headed caterpillar. E. adnatum, alpinum, hirsutum, montanum, palustre, parviflorum etc., Chamerion angustifolium: Mompha divisella

9a Galls on leaf margin => 10

9b Leaves usually with several clustered and converging on the ± stunted and distorted shoot, almost nest-like. Blades ± curled and deep green close to infestation. Epilobium, Chamerion spp.: Philaenus spumarius

10a Leaf blade usually rolled upwards or deflected => 12

10b Downward roll of leaf margin => 11

11a Roll loose, sometimes discoloured yellowish or reddish; weakly thickened, wrinkled outside, tuberculate. About 7–10 mm long or often joined into longer rolls. Larva whitish to cream-yellow. Chamerion angustifolium: Dasineura kiefferiana

11b Roll narrow, compact, usually not discoloured, less than 10 mm long, usually as concave emargination in the middle part of one side of leaf. Chamerion angustifolium: Cause unknown – ? gall mite

12a Margin deflected upwards. Chamerion angustifolium: Craspedolepta nebulosa

12b Downwardly deflected rolls of leaf margins. Chamerion angustifolium: Craspedolepta subpunctata

12c Leaf margin narrowly rolled upwards. Epidermis swollen, bladder-like. Chamerion angustifolium, Epilobium spp.: Phyllocoptes epilobiorum

13a Aphids yellowish- to red-brown or black => 14

13b Aphids yellowish or greenish in various gradations, colour never reddish tinged. Chamerion angustifolium, Epilobium spp.: Aphis praeterita

14a Basic colour of aphid red-brown => 15

14b Aphid black. Leaf margin rolled downwards. Chamerion angustifolium: Aphis fabae

15a On Chamerion angustifolium. Leaves partially curled and slightly deflected at margin, reddish discoloured, especially midrib; soon withering. Aphid about 2 mm long, basic colour yellow- to red-brown, usually red-violet by powdering; arranged in rows along the underside of the midrib. Chamerion angustifolium, occasionally Epilobium lanceolatum, obscurum: Aphis salicariae

15b On E. obscurum, palustre, parviflorum. Leaves curled in spring, red-spotted, on shoot tips of E. parviflorum sometimes accumulated, nest-like. Aphid about 2 mm long, red-brown, with six longitudinal rows of thick, grey-white spots of wax: Aphis pollinaria

15c On E. hirsutum. Aphids 2‒3 mm, reddish brown to almost blackish brown, each segment with a bright white transversal band of wax, interrupted only in the median line: Aphis epilobiaria

16a Surface of malformations covered with fruiting bodies of fungi => 17

16b Underside of basal green parts with many small warts, ± golden-yellow translucent, sometimes joined into ridges or crusts. Chamerion, Epilobium spp.: Synchytrium aureum

16c In small flat spots, 1–5 mm long, yellowish, soon browned, on E. alpestre, alsinifolium, palustre, occurs the smut fungus Doassansia epilobii

17a Malformations bearing brown sori or aecia => 18

17b Malformations covered by a white, ± dusted mycelium. Chamerion, Epilobium spp.: Podosphaera epilobii

18a Swellings expanded or pad- to bulge-like, with brown sori => 21

18b Malformations with aecia, confined or expanded, other spore forms not cecidogenic => 19

19a Malformations extending over large parts, often of many blades; fungus monoecious => 20

19b Similar malformations. Fungus host alternating. Spermogonia on leaf underside between cup-shaped aecia. Epilobium spp.: Puccinia veratri

20a On E. fleischeri. Mycelium pervading large parts of shoot. Internodes developing faster, slightly elongated, later on appearing stunted. Leaves sometimes partially infected, narrowed, pale-green, etiolated on diseased parts. Aecia densely arranged, widely distributed over the leaf underside, with broad, coarsely lacerate margin: Puccinia epilobii-fleischeri

20b Similar malformations on many other Epilobium species. Puccinia pulverulenta

21a On E. anagallidifolium, Chamerion angustifolium => 22

21b On many Epilobium species. Mycelium pervading large parts of etiolated shoot, telia easily dropping, developing in densely arranged red-brown sori, surrounded by a rim, almost aecidium-like, mainly on underside: Puccinia epilobii

22a On E. anagallidifolium. Shoots with extensive infestation; axial parts shortened, sterile. Leaves, especially in terminal parts, clustered; ± spoon-like bent upwards, curled. Plants often largely disfigured: Puccinia scandica

22b On Chamerion angustifolium. Sori arched, compact, almost black; on blades often on reddish discoloured spots, in rotund expanded bulges on veins and stem, surrounded by ruptured lead-grey epidermis. Bulges causing ± conspicuous distortions: Puccinia gigantea

23a On inflorescences or flowers => 24

23b Fruit slightly thickened, distorted, unopened. Containing a red caterpillar when mature. E. montanum, palustre, parviflorum, tetragonum: Mompha subbistrigella

24a Malformations on expanded parts of the inflorescence, caused by aphids => 25

24b Flower buds swollen into conical, or acutely barrel-shaped, unopened galls. Upper part of stalks ± swollen, calyx little changed, inner parts stunted and disfigured. Containing several yellowish to orange larvae. Chamerion angustifolium, Epilobium fleischeri, hirsutum, palustre: Dasineura epilobii

25a On E. montanum, parviflorum => 26

25b On Chamerion angustifolium. Stalk of inflorescence distinctly shortened with densely clustered largely stunted flower buds: Aphis frangulae

26a On E. montanum; stunting and malformation of inflorescence caused by white-powdered, dark-green aphids: Aphis praeterita

26b On E. parviflorum; caused by red-brown aphids: Aphis pollinaria

mod 15.ii.2020