Dictionary of Plant symbolism Y

Yarrow represents health and healing.

In the Bible Yeast is a symbol for sin. Unleavened bread represents Christ's body of flesh

Some examples:

Your glorying is not good. Know you not that a little leaven leavens the whole lump? (1 Corinthians 5:6-8)
You shall not offer the blood of my sacrifice with leaven; neither shall the sacrifice of the feast of the passover be left to the morning (Exodus 34:25). or You shall not offer the blood of my sacrifice with leavened bread; neither shall the fat of my sacrifice remain until the morning (Exodus 23:18).
No meat offering, which you shall bring to the LORD, shall be made with leaven: for you shall burn no leaven, nor any honey, in any offering of the Lord made by fire (Leviticus 2:11).

Dreaming about yeast (causing dough to rise) might represent: Patience and good things coming to those who wait; a carefree or light attitude
and the idea of focusing on nourishing yourself and others

A symbol of grief and mourning.
A feature of English churchyards.
It was grown in Celtic sacred groves where it was said to signify immortality.
This alternative symbolism was inherited by the Christian Church when it took over such places for its own worship.
The tree is rarely represented in Christian art.

The great tree which supports the universe. A wise eagle sits at the top; the roots are gnawed by Nithhogg and other serpents. The squirrel Ratatosk carries words of strife up and down. The tree binds Heaven, Earth and Hell together. Its branches; extend over the whole earth, its top reaches heavens and its roots descend to hell. The three Norns it under the tree, spinning the events of man's life.

The "yucca flower" is the state flower of New Mexico.