Put the sushi rice into a bowl of cold water and swirl and swish until the water turns white, then pour off the water, drain well. Put washed rice, wild rice and 2 1/4 cups water in pot on stove and bring to a simmer. Stir and cover, lower heat. Cook 15 minutes, until water is absorbed; stir, cover, and cool. Stir together vinegar and sugar, stir into rice.
While rice is cooking, heat oven to 400 degrees. Slice sweet potato into long french fry shapes, toss with maple, tamari and sesame oil on a sheet pan. Roast uncovered for 15 minutes, then turn the strips and bake for 20 minutes longer, until tender when pierced with a paring knife. Remove to rack to cool.
Slice the apple into 1/2 inch thick batons, about the same size as the sweet potato pieces. Mix the mayo with sage in a small cup.
To assemble, place a sheet of nori on a bamboo rolling mat. spread 3/4 cup cooked rice on each sheet of nori, leaving a strip about 1 inch wide along the top edge exposed. Sprinkle hazelnuts over the rice. Smear a teaspoon of mayonnaise across the bottom of the rice. Lay two rows of strips of sweet potato on the bottom third of the rice, place a couple rows of apple. Brush water on exposed nori. Roll up with even pressure, lay with seam side down to seal.
To make the flower petal shape, use the mat to shape by pressing down on one side after you've made the roll, using the mat to create the angle down to a point.
Let sit to firm up for a few seconds, then slice with moistened serrated knife into 6 to 8 slices per roll. Arrange each on a plate. Sprinkle hazelnuts over the slices, and garnish with wasabi, pickled ginger, and shoyu or tamari for dipping.