Dichotomous table for gallers on Mentha
by Hans Roskam
1a On parts above ground => 2
1b Nodular swellings on roots bearing side roots. Mentha spp.: Meloidogyne hapla
2a On inflorescences or flowers => 12
2b On vegetative organs => 3
3a Various malformations on shoots or leaves => 7
3b Localised galls of different size on stems or leaves => 4
4a Wart- or bulge-shaped galls caused by fungi => 5
4b Egg-shaped or conical galls, 4–6 mm long, 2–3 mm thick, often reddened swellings of shoot axis, usually situated above a higher node. Containing a curved larva, yellow when mature. M. aquatica, arvensis, pulegium, suaveolens: Squamapion vicinum
5a Galls contain spores => 6
5b Strongly swollen, sometimes conspicuously curved, yellowish or brownish-green bulges on basal stem parts; pads on leaf blades protruding on underside, on upperside often ± depressed, yellow, ± red-margined. Galls soon bearing cups, with dust of reddish-yellow spores. Mentha spp.: Puccinia menthae
6a Less than 1 mm long, golden-yellow translucent, multi-cellular warts on leaf underside, on petioles and stems; often many and occasionally joined into crusts or ridges. M. aquatica, longifolia: Synchytrium aureum
= On leaves of M. aquatica small, irregular globular or oval, often reddened nodules with a central cavity may be caused by the green alga Chlorochytrium rubrum.
6b Thick, black-brown bulges on stems, rarely on leaves, containing dark brown spore masses. M. aquatica: Physoderma menthae
7a At shoot tips or on leaves => 8
7b Plants stunted. Stem at base with bases of inserted leaves strongly swollen and spongy. Gall ± pale-green, necrotic. Mentha spp.: Ditylenchus dipsaci
8a Malformations not excessively pubescent => 10
8b Malformations covered by dense, abnormal pubescence => 9
9a Leaves or, if present, also neighbouring flower buds stalked on tips of main- and side shoots; all organs with ± dense yellowish-white pubescence on all sides. Hairs multi-cellular, branched. Sometimes excessively leafy, branched. Mentha spp.: Aceria megacera
9b Leaf blades of slightly stunted leaves with dense whitish pubescence. M. aquatica, arvensis, longifolia, mollissima, spicata: Aceria mentharia
10a Malformations caused by aphids => 11
10b Clustering of several leaves on bent shoot tips, usually stunted on one side and ± rolled and curled. Mentha spp.: Philaenus spumarius
11a Leaves on shoot tip strongly curled. Aphid green. Mentha spp.: Aphis affinis
11b Leaf blades of terminal leaves strongly curved and deflected. Aphid greenish-white. Mentha spp.: Ovatus crataegarius
12a Malformations of inflorescence => 14
12b Malformations on single or several flowers => 13
13a Flower buds swollen, unopened. Inner wall with mycelium. Containing an ochre-yellow larva. Mentha spp.: Asphondylia menthae
13b Flow ers slightly disfigured, only recognisable if closely examined. Mentha spp.: Peronospora stigmaticola
14a Malformations abnormally densely pubescent => 15
14b Malformations without abnormal pubescence. Accumulations of slightly stunted bracts and severely disfigured flowers at shoot tip of Mentha spp.: Eriophyes menthae
15a Flowers, mainly of terminal inflorescences, transformed into dense, white-pubescent, greened structures. Mentha spp.: Aceria megacera
15b Similar galls on M. arvensis, longifolia: Aceria mentharia