Holotype: ♀ (Fig. 2), Italia sept., Teriolis merid., Laatsch, 1000 m, 29.6.1987 e.l. (Silene otites 10.5.), leg. Huemer, slide GEL 1234 ♀ (TLMF).

Paratypes. Italy: 1 ♂, South Tyrol, Vinschgau, Schleiser Leiten, 1350 m, 6.7.2013, leg. Huemer, slide GEL 1215, dna barcode id TLMF Lep 12313 (TLMF); 1 ♂ [without abdomen], same data (TLMF); 1 ♀, same data, but 18.8.2013, slide GEL 1232, dna barcode id TLMF Lep 11883 (TLMF); 1 ♀, same data, but dna barcode id TLMF Lep 11882 (TLMF); 1 male [without abdomen], 8 ♀, same data, but 7.9.2013 (TLMF); 1 ♂, South Tyrol, Taufers, 1300 m, 22.8.1978, leg. Burmann, slide GU 86/041 P. Huemer (TLMF). Switzerland: 2 ♀, Wallis, Martigny-Rosel, 460 m, 28.6.–14.7.1983 e.l. (Silene otites), leg. Whitebread (Naturhistorisches Museum Basel, Switzerland). Greece: 1 ♀, Larisa, Ossa Oros, 1.5 km N Spilia, 940 m, 13.6.1988 e.l. (Silene nutans), leg. Huemer (TLMF).

Caryocolum crypticum sp. n. is externally similar to several other species of the genus and can be best recognized by the largely unmarked forewings with cream costal and tornal spots. From its closest relatives Caryocolum amaurella and Caryocolum iranicum it differs by the rusty brown distal half of the thorax and the concolorous tegulae, the dark brown forewings with rusty brown scales, and the cream colours of the costal and tornal spots. The male genitalia of Caryocolum crypticum are very similar to those of Caryocolum amaurella but the valva is more slender and slightly longer (see Figs 6–7, 10–11 versus 8–9, 12–13). The similar Caryocolum iranicum differs by the shape of the sacculus with almost straight dorsal margin (see Huemer 1989b: Figs 14–16). However, the most striking diagnostic characters of the new species are found in the female genitalia which differ from Caryocolum amaurella particularly by the short lateral sclerites of the ductus bursae and the much longer and more slender signum hook (see Figs 14–15 versus 16–17). The female genitalia furthermore differ from Caryocolum iranicum by the weakly cup-shaped rather than funnel-shaped antrum, shorter lateral sclerites of the ductus bursae, and the shorter apophysis anterior which is almost twice the length of segment VIII in Caryocolum iranicum.

Adult (Figs 2–3). Wingspan 10.5-14 mm. Segment 2 of labial palpus with a few cream-coloured scales on inner and upper surface, blackish brown on outer and lower surface; segment 3 almost black with light tip. Antenna black, indistinctly lighter ringed. Head with light yellow frons and black neck; thorax blackish brown with rusty brown posterior part; tegulae rusty brown except for blackish brown base. Forewing blackish brown, mottled with some rusty brown, particularly in proximal half; supplementary black spots in fold and in cell obscure; costal and tornal spot small, cream, separated. Hindwing light grey.

Variation. No variation observed except for size, which differs considerably in two reared specimens from Italy and Greece.

Male genitalia (Figs 6–7, 10–11). Uncus subovate; tegumen stout; transtilla membranous; valva moderately short and slender, digitate, apex rounded; sacculus short, with angular ventral and weakly convex dorsal margin, apically pointed; posterior margin of vinculum with deep medial emargination and slight medial incision, two pairs of short processes developed; saccus long, comparatively broad at base, distal part gradually tapered; phallus long and slender, weakly curved, with some minute cornuti apically.

Female genitalia (Figs 14–15). Segment VIII without processes, subgenital plate sub-triangular, with numerous narrow folds, separated from sclerotized lateral plates by membranous zone; apophysis anterior about length of segment VIII; antrum short, about one quarter length of apophysis anterior, nearly cup-shaped; posterior part of ductus bursae with pair of short sclerites, extending to middle of apophysis anterior, and with two tiny sclerites anteriorly; signum with crescent-shaped base, long and slender, strongly bent hook.

Molecular data. The intraspecific divergence of the barcode region is low with mean intraspecific divergence of 0.21% and maximum intraspecific divergence of 0.31% (n=3). The distance to the nearest neighbour Caryocolum mucronatella is 5.41%, the divergence to the morphologically closest Caryocolum amaurella is 6.82%.

The name “crypticum” refers to the cryptic morphology of the species and is derived from the latinized adjective crypticus.

The species is known from widely separated localities in northern Italy, Switzerland and Greece, indicating a more widespread distribution in Sub-Mediterranean and Mediterranean Europe. However, the host-plants are much more widespread, ranging to northern Europe in the north and to Central Asia in the east. No sympatric occurrence with Caryocolum amaurella is reported though the two taxa can occur close to one another in the Alps.

The larva has been found in early spring, feeding in the stem of Silene otites (L.) Wibel (Caryophyllaceae) (Burmann 1990) and Silene nutans L. (Huemer 1989) but detailed descriptions of feeding habits and larval morphology are missing. The adult occurs from early July (reared material dates from mid-June to mid-July) to September and it is attracted to light. Caryocolum crypticum prefers xerophilous steppes and rocky habitats with sparse vegetation. Vertical distribution: from about 500 to 1300 m, restricted to mountainous areas.

Huemer (1988) already examined females reared from Silene otites in Switzerland by Whitebread but in the absence of males considered them as deviating Caryocolum amaurella.

The majority of collected material belongs to females whereas Caryocolum amaurella is mainly known from the male sex. This may indicate differences in attraction to artificial lights or a female-biased sex ratio in Caryocolum crypticum.