A stem square with two or three options, and for each option a petal: a few squares that option would squeeze. Whichever way the stem goes, a petal ends up holding the same number, so a square that sees that number in every petal can't have it.
123456789
123456789
67
4
3
8
5
2
1
9
1
67
9
4
27
5
3
8
5
2
8
1
9
3
4
6
7
4
8
1
6
9
37
9
5
4
1
2
6
8
23
2
9
8
1
4
2
3
7
9
8
4
1
9
5
4
7
8
1
3
2
6
8
1
6
3
2
4
7
9
5
The stemThe petalsLoses a pencil mark
The name
The stem and its petals: each option of the stem grows its own branch, and the branches meet at the number they share.
How to spot one
Start from a square with two or three options. For each option, look for squares it would squeeze down to one shared number. If every branch ends on the same number, check what sees them all.
What it gives you
One removal, usually. Death Blossoms turn up on the hardest boards, once the wings and chains have run out.
Practise Death Blossom
Boards that need it, with the owl's hints when you're stuck.