The flowers and other flora that grow on graves is called Grave Growth.

For burials in the ground the growth is flowers.

For burials in crypts, sarcophagi, or urns the growth is lichens, moss, or fungi.

Graves, graveyards/cemeteries, battlefields, and other places of mass death whether by disease or slaughter will be covered with such growth.

The common folk will all know about these signs of death and burial.

The source of these growths is debated.

How do they only grow over graves?

How do the seeds find the soil to take root?

Possible Explanations Are Many:

Soul “fragments” are actually the seeds of growth.

The blood, bones, or organs contain the seeds.

The gods themselves plant them. (Or the god with death in their portfolio.)

Harvesters or Gatherers of the souls of the dead plant them. (Think like Valkyries retrieving Viking warriors.)

More Signs

While the living flowers or other flora signify a grave, when those flowers die, it indicates the body that rested there has risen in undeath.

Use In Game

The party comes upon a huge field of grave growth flowers. This is a sign of an ancient graveyard or necropolis.

If the field is of dead grave growth, then there is a past or current army of the dead.

Names

I’ve struggled to some up with a specific name for such flowers. This is an idea wanting a name. If you use it in your game, come up with your own name for such growths.

Death flowers doesn’t fit. Grave flowers is a generic term like grave growth.

Grave Watch or Grave’s Watch, as if the flowers are watching or standing watch over the grave sounds cool.

Death Blossom sounds cool, but is already taken by The Last Starfighter.

Death Floret sort of works. Grave Floret sounds better.

Final Floret, Black Floret, Red Floret…. Still not quite it.

There’s a word I can’t quite bring to mind. Searching for synonyms didn’t give it.

Source

This idea came to me while I was mowing the yard. When I took a break for water, I scribbled down my idea before I forgot it.

I have no idea if there are such things in the real world, or if any fantasy world has something like this.

A quick internet search lead to what are the most common plants to plan at a gravesite. I found one reference to a carnivorous plant in an RPG wiki, but nothing like what I envision.