There are two slightly different looking kinds of Wildwood flowers (a glowing kind with protruding orange blossoms, and a non-glowing kind) that will turn into the same (bright glowing) kind when harvested.
These flowers are an ingredient of Poison Resistance Potions, to be crafted in your Crafting Menu (opened by typing "q" as the default key) or at any Crafting Table in older worlds.
Wildwood Flowers can also be used as an ingredient in Basic Health Potions, Stone Mining Cells, Taming Collars, Golden Potions and Stamina Regeneration Potions - in recipes where you can choose from different possible flowers by browsing through the options with left-click on the flower-icon showing two small golden arrows.
Wildwood flowers have the shape of blocks and can be placed.
Unlike other flowers, Wildwood flowers give off a rather bright glow, similar to Glowing Mushrooms. Still, when placed as a light source, they cannot prevent the spawning of night creatures, if other blocks that these creatures would usually spawn on are close (like Sand below such flower-blocks can make Night Rocksters spawn in darkness during the night).
Wildwood-trees cannot be grown from Saplings currently (as of R26 in December 2015).
More Wildwood Flowers will - slowly - grow on Wildwood Leaves and also on Dark Wildwood Leaves with time, so you can lay out flat artificial biomes made from these leaves and wait for a few (real time) days until you can collect one or two Wildwood Flowers every couple of days or so. The same goes for Blue Flowers, Yellow Flower and Red Flowers; not for Autumnwood Flowers nor Weepwood Flowers though.
A faster method to get more Wildwood Flowers is to simply place blocks of Wildwood Flowers on the ground and pick them up again - once in a while you will obtain 2 flowers at once when doing that.