Osmia maritima is one of two currently known species of the xanthomelana species group in North America (species with more or less shining ventral area of the propodeal triangle, apically widened mandible in females, and distinctly swollen gonoforceps in males). Females of Osmia maritima are distinguished from the other North American xanthomelana species group member, Osmia nearctica, by characteristics of the mandible, outer hind tibial spur, and clypeus: the mandible has a third tooth that is recessed below a distinct carina between the second and fourth teeth (Fig. 8) (Osmia nearctica with the third tooth in the same plane as the second and fourth teeth and no carina, Fig. 10); the outer hind tibial spur is strongly curved apically (Osmia nearctica with outer hind tibial spur weakly curved apically), and the apical truncation of the clypeus is not distinctly set apart from the lateral apical margin of the clypeus, Fig. 55 (Osmia nearctica with the apical truncation forming a 90 degree angle with the lateral apical margin of the clypeus, Fig. 35). Females of Osmia maritima also have almost entirely black pubescence on the clypeus (significant amounts of light hairs throughout the clypeus in Osmia nearctica) and longer hair on the galea in dorsal view.

Males of Osmia maritima are distinguished from Osmia nearctica by their relatively long, sparse hairs on the lower surface of the flagellar segments (Osmia nearctica with these hairs microscopic) and weakly emarginate S2 (Osmia nearctica with S2 midapical margin not emarginate).

In the Nearctic, Osmia maritima is known only from the Northwest Territories and Alaska. In the Palearctic, Osmia maritima is known from the Netherlands, Germany, Denmark, Norway, Sweden, and Finland east to Mongolia and through Russia to Far Eastern Siberia (Müller 2010).

We have not found any male specimens of Osmia maritima in the material of nearctic Osmia available to us. It is possible that once male specimens are discovered they may prove to be a distinct species from their palearctic relatives (if, as in Osmia aquilonaria, the novel diagnostic characters of the species are only found in the males); however, since a holarctic distribution is well established for other Osmia species (e.g., Osmia inermis and Osmia nigriventris), until proven otherwise we conservatively retain the name Osmia maritima for this species. Interestingly, there appear to be two female morphs of Osmia maritima. Specimens from Alaska and the Russian Far East share pale hair on the paraocular area and mesepisternum and scarcely sculptured apical areas on T2 and T3; females from the Northwest Territories and western Europe have dark hair on the paraocular area and mesepisternum and microsculptured apical areas of T2 and T3.

Osmia maritima from the Palearctic is known to be polylectic and nests in sandy soil with cells composed of chewed leaves and sand grains (Müller 2010 and references therein).

CANADA: NORTHWEST TERRITORIES, Inuvik Region, 17 June 1971 (1♀, Ottawa), 20–25 June 1971 (3♀, Ottawa), 28–30 June 1971 (1♀, Ottawa), 11 July 1948 (1♀, Ottawa); NETHERLANDS: Terschelling, 2 June 1969 (1♂, 1♀, Logan); RUSSIA: Siberia, 5 July 1992 (1♂, Davis), 12 July 1992 (1♀, Davis); USA: ALASKA, Fairbanks North Star Borough, 31 July 1985 (1♀, Davis); Southeast Fairbanks Census Area, 21 June 1984, Oxytropis campestris (3♀, Davis); Yukon-Koyukuk Census Area, 17 May 1991, Dodecatheon frigidum (1♀, Davis), 19 June 1992, Penstemon gormanii (1♀, Davis).