Dichotomous table for gallers on Cerastium

by Hans Roskam

1a On inflorescences, flowers or fruits => 16

1b On vegetative organs => 2

2a Plant completely or largely etiolated. Internodes elongated and lanky; leaf blades narrowed and pale green; with expanded sori of fungus on undersides => 15

2b Malformations otherwise => 3

3a Galls at tip of shoots => 8

3b Malformations of lower parts or leaves with locally defined gall => 4

4a Galls mainly on stems => 7

4b Galls wart- or pad-shaped, mainly on leaves => 5

5a Many galls, hardly 1 mm long, multicellular, ± hemispherical, usually on underside of basal leaves, also on stems; sometimes ± coalescing ridge- or crust-like => 6

5b Leaf blades with rotund, usually circularly arranged, sometimes slightly arched sori on underside of leaf veins. Petiole or stem with more densely arranged pads on oblong-oval bulges, about 3–6 mm long, compact, often yellow margined, weak, sometimes curved. Sori usually compact, bearing brown telia. Cerastium spp.: Puccinia arenariae

= Puccinia hysteriiformis has also been reported from Cerastium. This rust has black telia

6a Small pearl-like warts, with central, golden-yellow translucent nutritive cells. C. fontanum subsp. vulgare: Synchytrium aureum

6b Small warts greenish, multicellular, later on usually yellow-red or brown. C. glomeratum: Synchytrium stellariae

7a Stem with localised swellings. C. semidecandrum: Unidentified gall midge

7b Stem swollen and spongy from base over several internodes; adjacent leaves stunted, the basal parts often galled similarly. Infestation of older plants often results in ± expanded, curved swellings of stem. Galls always pale green, with ± rugose surface. Cerastium spp.: Ditylenchus dipsaci

8a Galls on shoot tips. Midge- or fungus galls => 13

8b Malformations expanded over ± substantial parts of terminal parts of shoot => 9

9a Galls lacking conspicuous pubescence => 10

9b Leaves clustered on shortened shoot tip, ± adpressed to the stem, abnormally pubescent. Sometimes branching excessively. C. arvense, diffusum, fontanum & subsp. vulgare, glomeratum, sylvaticum: Aceria cerastii

10a Several leaf pairs enlarged, keel- or spoon-like, curved, on shortened shoot axis clustered; galls rotund to oblong-oval, tuft- or almost cone-shaped => 12

10b Leaves with several disfigured, not clustered cone-like => 11

11a Upper part of stem locally severely stunted, sometimes curved, leaves accumulated; variously converging, nest-like ± curled and deep green. Cerastium spp.: Philaenus spumarius

11b Many leaves at the end of weakly stunted shoots deflected; ± curled. Cerastium spp.: Myzus certus

12a Gall frail, oblong-oval to spindle-shaped; up to about 20 mm long. Cerastium spp.: Trioza cerastii

12b Tuft-like malformations of shoot tips. C. fontanum & subsp. vulgare, glomeratum, moesiacum: Dasineura cerastii

12c Galls similar, often paler, yellowish, more rotund or egg-shaped; at first with green, white powdered aphids, about 2 mm long on the inner side of leaves. Aphid free-living later on the terminal shoot parts. Cerastium spp.: Brachycolus cerastii

13a Upper leaf pair folded together, containing a single or several midge larvae => 14

13b hoot tip markedly stunted. Leaves bushy, clustered together, ± disfigured, pale, rudiments of flowers, if present, ± largely atrophied; transforming the whole tip into a ± closed gall; pale red-brown spore masses develop in its tissue. C. arvense: Thecaphora alsinearum

14a Terminal pair of leaves enlarged, thickened, bulging. Larva red or orange. C. alpinum, arvense, fontanum subsp. vulgare, glomeratum, grandiflorum: Dasineura lotharingiae

14b Terminal pair of leaves folded together, remaining small; containing a single larva. C. arvense: Unidentified gall midge

15a Leaves, also stem parts, as well as exceptionally developed inflorescence stems and calyx leaves with many, scattered, small orange-yellow uredinia. Cerastium spp.: Melampsorella caryophyllacearum

15b Systemic diseased shoots growing erect, etiolated. Leaves pale green, development stunted, sometimes appearing slightly thickened, covered on underside with branched conidiophores. Rudiments of inflorescences, if present, stunted in all their parts. Flower buds ± globularly swollen, unopened, loosely covered externally with conidiophores. Fungus present during whole vegetative period, mainly in spring and autumn. Cerastium spp.: Peronospora sp.

16a On inflorescences or flowers => 17

16b Capsule weakly swollen. Larvae orange-coloured. C. fontanum subsp. vulgare, pumilum, semidecandrum. Dasineura fructum

17a Inflorescence ± disfigured; flowers greened or leafy Axis shortened; flowers ± leafy; stamens and ovaries crumpled or sometimes transformed into a ± rotund ball of leafy organs. Cerastium spp.: Trioza cerastii

17b Axis of inflorescence stunted; flower buds or fruits globularly swollen, unopened => 18

18a Malformations caused by fungi => 19

18b Globular swollen bud, contains a single red midge larva. C. arvense, fontanum subsp. vulgare, glomeratum, pumilum, semidecandrum: Dasineura lotharingiae

18c Fruit swollen, also the petiole is thickened; containing a weevil larva. C. fontanum subsp. vulgare: Sibinia subtriangulifera

19a Flower buds or flowers usually distinctly stalked => 20

19b Flower buds with very short, strongly swollen stalk, only slightly protruding from the often tuft-like disfigured shoot tip, stunted early and swollen; pale red-brown spore masses inside the swollen tissue. C. arvense: Thecaphora alsinearum

20a Inflorescence unchanged and flowers outwardly only slightly changed. Ovaries slightly disfigured. Seed rudiments, also -stalks and ridges at first slightly swollen, soon containing brownish-violet spore masses, dusting when capsule opens. Cerastium spp.: Microbotryum duriaeanum

20b Flower buds on ± shortened stalks distinctly stunted and swollen, at surface soon covered with conidiophores; corresponding down usually simultaneously occurring on adjacent vegetative organs. Cerastium spp.: Peronospora sp.

mod 15.iii.2020