Preheat oven to 350˚F. Grease and flour a 10" round cake tin or baking dish.
Cut rhubarb into roughly 2" long x 1/2" wide pieces. You may have to cut rhubarb in half or into quarters lengthwise first if the stalks are very thick. Let rhubarb pieces sit in a small bowl with 2 tablespoons of maple syrup while you prepare the cake batter.
Whisk together flax meal and coconut milk until frothy and let sit.
Whisk together flour, almond meal, sugar, baking powder and salt in a separate bowl.
Add oil, remaining maple syrup, rosewater, almond and vanilla extracts to the the coconut milk-flax meal mixture and whisk everything together.
Add wet mixture to dry mixture and stir with rubber spatula to combine. Do not whisk and avoid over-mixing.
Pour batter into prepared baking dish and spread evenly with a spatula. Arrange rhubarb pieces in any pattern you like or randomly. Shown here is a 3 rowed basket-weave/cross-hatch pattern. Sprinkle top with sliced almonds.
Bake at 350˚F until golden brown and a toothpick inserted comes out clean, about 35-40 minutes.
Let cake cool on a rack to room temperature before slicing. Top with fresh or dried edible rose petals to garnish before serving.