This caption particularly applies to the dried mushrooms in the photo set, which were photographed today, 4 days after collection:
These mushrooms were collected in the same area (intermingling within about a 10 foot diameter) in oak woodland. They were very similar, except the ones on the far right have the distinctive, strong odor of maple syrup. The ones on the left have a faint smell of maple syrup and on the average a thicker stipe (both fresh and dried). I'm calling the mushrooms on the left Lactarius rufulus and the ones on the right Lactarius rubidus. This sample of L. rubidus also was generally darker than L. rufulus. While fresh the difference wasn't as great as when they dried. Also, all of these mushrooms were starting to dry out in the field. Though faint L. rubidus already was developing its sweet, maple syrup odor. L. rufulus, however, had little odor at all in the field; it did not develop it's faint, sweet odor of maple syrup until it was dried out completely. Lastly, note that in the photo of the dried mushrooms with the stipes in the foreground that L. rubidus tended toward hollow stipes and L. rufulus tended toward a solid stipe. Just to clarify the last two photos of this set of photos of the dried mushrooms on a paper towel each have both types of lactarius, the left side of the paper towel being L. rufulus (that's what I think, anyway).
Lactarius is a genus of mushroom-producing fungi. The genus, collectively known commonly as milk-caps, are characterized by the fact that they exude a milky fluid ('latex') if cut or damaged. Like the genus Russula, with which they are grouped in the family Russulaceae, their flesh has a distinctive brittle consistency.