Diagnosis. This species is recognized by its very small size and the strongly inwardly oblique fascia on the distal part of the forewing. The male genitalia of tormentillella, S. dryadella, S. poterii, S. filipendulae and S. ulmariae each have a large and variable apical cornutus in the aedeagus; tormentillella differs from the three last mentioned in having a proximal row of strong cornuti in the aedeagus; the tip of the valva is blunter in tormentillella than in dryadella, and dryadella has about 30 proximal cornuti in the aedeagus in contrast to tormentillella's 15 to 20. The female genitalia are characteristic by the narrow vestibulum.
Male. Wingspan: 3.3-3.8 mm. Head: frontal tuft grey-brown, vertex black; collar dark grey; scape white; antenna three-quarters length of forewing, dark grey-brown. Forewing: area proximal to fascia greenish golden, purplish brown towards fascia; fascia shining silvery, distinctly inwardly oblique, to four-fifths on costa and two-thirds on dorsum; distal to fascia purplish brown; terminal cilia pale grey-brown. Hindwing and cilia pale grey. Abdomen dark grey. Female. Wingspan: 3.5-4.2 mm. Darker than male. Frontal tuft black. Antenna two-thirds length of forewing. Forewing with more contrasting wing pattern, shining brownish golden, before and beyond fascia dark purplish brown; fascia more distinct than in male, greenish silvery. Hindwing grey. Abdomen dark grey to black. Male genitalia. Vinculum short; anterior margin almost straight to very shallowly emarginate. Uncus broad, subtriangular; medial notch variably broad, deep; paramedial notches small to indistinct. Valva broad, tip broadly rounded or with broad, triangular distal process. Transtilla broad and relatively long, sublateral processes very short. Juxta present. Aedeagus about as long as genital capsule; with a long, usually curved, large cornutus and a few smaller spines near tip, proximal part with 15-20 strong cornuti in a row and many fine spines. Female genitalia. Corpus bursae without pectinations. Vestibulum narrow. Accessory sac smaller than corpus bursae. Ductus spermathecae without spines. Apophyses sharply pointed.
Host plants: Potentilla aurea, P. crantzii, P. erecta, P. tabernaemontani and possibly other Potentilla species. Egg: on underside of leaf. Larva: yellow. Mine : at first a narrow linear mine following a vein or the leaf margin, with frass in an uninterrupted central line; second half widening into a blotch, sometimes occupying the entire leaf, with frass irregularly scattered. Cocoon: yellowish brown.
Not in Denmark and Fennoscandia. - In Germany from Hartz and northern DDR, Eifel and Regensburg, Poland, Austria, Switzerland, N. Italy and S. France (East Pyrenees), Roumania.
Voltinism: one generation per year in higher altitudes, and two annual generations in lower localities. Mines from late August and September-October. A mainly alpine species from alpine meadows, along roadsides and stony places to about 2200 m altitude, but also found in the lower mountains and several lowland localities in C. Europe.
Description based on Johansson and Nielsen (1990)