The complexities of Schleswig-Holstein run deep. Here’s Emil Nolde, an artist born south of the German-Danish border and steeped in the marshy mysteries and primal romanticism of that landscape. In 1920, he sees his region, and himself, become Danish following a post-Versailles plebiscite. An already well-established German nationalist bent — pronounced despite, or perhaps because of, his shifting national identity and shaky grasp of the German language — is inflamed. He moves back across the new border before eventually joining the local branch of the Nazi party and writing a volume of autobiography entitled, Jahre der Kämpfe in which he rails against the Jewish dominance of the art world.

National Socialism attracted Nolde and he saw the Nazis as an opportunity for the German avant-garde. He envisaged his model of expressionism becoming the cultural face of the nation and a new wave of artists being empowered by the state to become the modern equals of Dürer, Grünewald and Holbein. The authorities rewarded this giddy optimism by confiscating more of Nolde’s works (1,052) than those of any other artist during the purge against ‘degenerate’ art and, from 1941, forbidding him to buy materials or engage in any professional artistic practice whatsoever.

It’s easy to see why Nolde’s relentless assault of thickly applied colour — lurid landscapes beneath sickly skies and crude, wide-eyed, yellow-skinned figures — offended Hitler’s plodding artistic ideals. The landscapes are turbulent places, his city dwellers dyspeptic, heavy-eyed barflies or decadent cabaret patrons. Most damning of all are the religious works, which converse far more readily with the emotionally agonised figures of Grünewald’s Northern Renaissance than they do with any Kinder, Küche, Kirche crap.

In the immediate aftermath of the annexation of his homeland, Nolde painted ‘Paradise Lost’, an image of Adam and Eve after the expulsion. A surly, bearded man sits beside a lumpen yellow woman with bewildered blue eyes. Menaced by a distant lion and teased by the serpent between them, the figures look dejected, lonely and thoroughly depressed. It’s not hard to read this very human painting as an allegory for Nolde’s own suddenly ‘lost’ paradise and floundering identity.

The religious works, all housed together here for maximum impact, though painted years apart, get stranger. ‘Ecstasy’ is a remarkably odd painting. Purporting to illustrate the exact moment of Jesus’s conception, it shows a bright yellow and purple woman, naked, breasts jutting forward, legs slightly parted, with massive, stunned eyes, a gaping scarlet smear of a mouth and a black nest of pubic hair. ‘Should one not be allowed to paint something like this?’ Nolde challenged.

This glaring, corporeal and sexualised Virgin represents true expressionism, drenched in emotion and revelling in the resonant possibilities of colour theory. Hanging next to it is the triptych, ‘Martyrdom’, three images of Christian suffering. It’s a powerfully emotive painting but the overt anti-Semitism of the snarling, sniggering, hook-nosed figures that crowd around the crucified Christ in the centre is hideous.

Elsewhere, Nolde embraces the Urmensch (primitive man), painting ethnographic collections and travelling to New Guinea to make striking, if rather ‘noble savage’ style portraits and fabulous loose watercolour studies of the aboriginals. Fundamentally, however, Nolde’s world is very, very German and, although influenced by contemporary French and Scandinavian artists, it is the Germanic cultural language that dominates his drawing, painting and printmaking.

Nolde may have felt ostracised by perceived Jewish forces but he was a respected artist associated with both Die Brücke and Der Blaue Reiter, the two groups that led the German expressionist charge. The problem may have been that in reality, Nolde was a little excluded everywhere, not quite German enough, despite his intense nationalistic efforts, not quite Danish and, despite much time spent in the city, never quite a Berliner. His urban paintings share an uncomfortable, queasy look and there’s a perceptible distance between Nolde and his subjects who are often presented with their backs turned to him.

Perhaps the only place Nolde really felt at home was in the wide tracts of Schleswig-Holstein, amongst the gnarly peasants that populate his early work.

His best landscapes came from this place too, flat horizons, turbulent seas, all lurking beneath demonstrative skies. Compare the confident handling of ‘The Sea B’, where heavy, violet-tinged clouds billow over a distant slick of orange light and a churning indigo sea with the clumsy and soulless ‘Bay’, a lousy, sub-Gauguin tropical landscape.

Sequestered in his northern refuge during the war but officially forbidden to paint, Nolde made hundreds of small watercolours, his ‘unpainted paintings’. These strange, heavily worked little studies end the exhibition. Obscure and stylistically adventurous, they explore an imagined world of animals and figures, like illustrations for an unwritten fairy tale. Unable to paint outdoors, betrayed by the party he trusted, Nolde took refuge in what he called a ‘landscape full of miracles and delights’, an unsullied Schleswig-Holstein of the mind.