Dichotomous table for gallers on Scabiosa
by Hans Roskam
1a On parts above ground => 2
1b Roots with small cylindrical-spindle-shaped swellings, 3–4 mm long, and considerable formation of side roots: Meloidogyne hapla
2a Malformations of inflorescences or flowers => 11
2b Malformations on vegetative parts => 3
3a On leaves, shoot tips or stems => 4
3b Many buds on root collar develop into short, laterally and variously growing, ± clustered stump-like, succulent shoots: Aphelenchoides fragariae and/or Rhodococcus fascians
4a Malformations on leaves, with or without inclusion of tips or axial parts of shoots => 7
4b Galls on axial parts of shoots => 5
5a Inducers inside galls => 6
5b Stem locally stunted, with irregular spindle- or bulge-shaped swellings and often strongly distorted or irregularly bent, up to a right-angle; often with several rimmed depressions which contain scale insects below scales. S. ochroleuca: Planchonia arabidis
6a Shoot axis, especially at base, with nodular, succulent, dark red-brown swelling. Containing a caterpillar. S. atropurprurea, canescens, columbaria, ochroleuca, triandra: Alucita grammodactyla
6b Axial parts of flowering shoots with oblong-oval swelling, up to 4 mm long, often ± crimson-red. Containing a pale-yellow caterpillar with yellow-brown head. S. atropurprurea, canescens, columbaria, ochroleuca, triandra: Alucita grammodactyla
7a Galls with abnormal, ± white pubescence => 10
7b Malformations lacking conspicuous pubescence => 8
8a Malformations caused by aphids => 9
8b Leaves terminally on vegetative shoots ± distinctly clustered. Leaf blades narrowed and ± with protuberances. Scabiosa spp.: Aceria squalida
9a Shoot axis variously stunted. Leaves curved and curled. S. columbaria, ochroleuca, triandra: Aphis thomasi
9b Similar malformations. S. atropurpurea, columbaria, ochroleuca, triandra: Aphis confusa
10a Leaves sometimes densely clustered on tips of non-flowering sometimes stunted main and side shoots; leaf blades narrowed, rolled upwards, ± weaved and tuberculate, especially stunted basally and over often larger expansion ± densely white felt-like pubescent. In strongly infected plants also white erinea also locally on sometimes strongly swollen leaf- or stem parts. Also inflorescences may be severely stunted and white felt-like over large expansion. Scabiosa spp.: Aceria squalida
10b Inside leaf rosette two or more leaves remain erect. Their base is stunted, and severely stunted leaf blades are swollen, mussel-like, thickened and at least the basal part on both sides densely covered with long, white hairs, resulting in a compact gall. Sometimes with similar galls on lateral buds or tips of severely stunted shoots. Containing several white, later on ± reddened larvae. S. columbaria: Jaapiella scabiosae
11a Malformations lacking conspicuous additional pubescence => 12
11b All parts of still young, ± stalked capitula severely stunted and often densely pubescent. Exceptionally also further developed inflorescences affected, of which almost only the involucral bracts are ± disfigured and densely haired. Scabiosa spp.: Aceria squalida
12a Malformations caused by animals => 14
12b Malformations caused by fungi => 13
13a Anthers, sometimes also filaments, ± shortened and swollen, soon filled with dirty straw-coloured spore masses. S. columbaria & subsp. balcanica, lucida, ochroleuca, triandra: Microbotryum intermedium
13b Flowers variously stunted or distorted; sometimes with ± petal-like transformed anthers. Diseased parts soon covered with a loose, dark down of branched conidiophores. S. columbaria, lucida, ochroleuca: Peronospora violacea
14a Malformations of almost entire flower head => 15
14b On ± fully developed capitule, single to many involucral bracts are distinctly elongated, thread-like, rolled upwards, not additionally pubescent and often bumpy and curved. Also some greened receptacular bracts and even sexual organs may be similarly galled. Scabiosa spp.: Aceria squalida
15a Malformation of complete flower head. Flowers greened, ± stalked, and developing new shoots (phyllanthy). Scabiosa spp.: Aceria squalida
15b Flowers unopened, swollen. Containing several jumping midge larvae. S. columbaria: Contarinia scabiosae