Thanks, Jim Carroll, for citing the Funk and Wagnall's. I was going to do that myself, but the book is out of my reach at the moment, and damned heavy to boot.

The song thyme song that sticks my strongly in my head (that I learned from a Jean Ritchie album, if I recall correctly) is In My Garden Grew Plenty of Thyme.

The third verse mentions the rose, and then quickly shifts focus to the willow, where it remains for the fourth:

In June the red rose is in bloom
But that was no flower for me
I plucked at the bud and it pricked me to blood
And I gazed on a willow tree (2x)

And the willow tree it may twist
And the willow tree it may twine
I would I were clasped in my lover's arms fast
For 'tis he who has stolen my Thyme (2x)

This may seem like a complete non-sequitor, but back in the day before Hallmark and American Greeting, handing someone a sprig of willow was considered a polite way of telling them that their love is unrequited, because a willow branch will take root and grow again into a new tree quite easily (Outside a summer house built by my great(?)-grandfather, there grows a tall willow tree which was said to have sprouted from a switch that someone cut as an impromptu riding crop, then stuck in the ground by the door when he got home). So, in effect you're saying: "Sorry I broke your heart, kid; I hope it doesn't stay broken for long." And then, the rejected lover could wear the sprig on their person to say to the world: "No, I don't feel like going to the party. My boy/girlfriend just broke up with me.

This goes back at least Shakespeare's day. This passage is spoken by Benedick, in Much Ado About Nothing:

Troth, my lord, I have played the part of Lady Fame.
I found him here as melancholy as a lodge in a
warren: I told him, and I think I told him true,
that your grace had got the good will of this young
lady; and I offered him my company to a willow-tree,
either to make him a garland, as being forsaken, or
to bind him up a rod, as being worthy to be whipped.

So, in In My Garden, at least, it seems as if the lad was all full of love until they have sex, whereupon he turns around and breaks up with the singer (to move on to his next conquest?).