Quite a vague description.
One possibility is the Darkover series by Marion Zimmer Bradley.
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First answer is correct, definitely Darkover series by Marion Zimmer Bradley.
First book is "Darkover Landfall" Spaceship crash lands on a distant planet after going off course.
Local plant pollen and spores have drug like effects and bring out latent psychic powers in certain families who become royalty over generations.
The series covers the culture that evolves and the effect when human contact is reestablished centuries later.
I remember reading the entire series in the late 70's/early 80's http://darkover.wikia.com/wiki/Darkover_Landfall
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I agree that Darkover is very likely, but also the Cycle of Fire books by Janny Wurts has similar ideas.
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Perhaps the Coldfire Trilogy by C.S. Friedman?
It takes place on a planet colonized over a millennium prior by humans from Earth.
The planet has an energy field which reacts to the wishes and desires of the colonists, and this manifests as magic.
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It's possible you're thinking of the Coldfire Trilogy by C. S. Friedman.
It's set on a fantasy world with magic where it turns out that current civilization is the result of a failed future society.
Things that don't match include that the order is different — it starts in the magic society and we later learn about the futuristic underpinnings — and that the ship didn't crash, but rather, the colonization attempt failed due to the technology failing.
I don't remember anything specific about the plants, but the first book involved an evil forest and the latter books were set in other strange environs.
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It could be L.E. Modessit Jr's.
Recluce Saga .
In Fall of Angels , a modern spacefaring (and -fighting) ship with a small crew is forced into an alternate universe where much technology fails and magic works.
Crew members find themselves with new abilities such as "Order Magic", healing, night vision, and prophetic visions.
They struggle to found a working society that will last despite being mostly women surrounded by excessively chauvinistic nations.
The other books in the series mostly deal with their descendants in a world where magic works, and technology is largely limited by choice as it strengthens "Chaos Magic".
The overall theme of the series is the eternal struggle between Order and Chaos, each of which can be manipulated by adepts as Magic.
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It could also, at a stretch, be the Well World series by Jack Chalker, which starts with "Midnight at the Well of Souls".
In that first book, a spacecraft gets caught up in a gateway to the Well World, and the people on board are sent to a variety of regions and are transformed to different species based on where they go.
Following books in the series cover various power struggles both in the outer universe and on the Well World, where some of the geographic regions are coded to stop any technology working but in exchange have a form of magic.
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The True Game series (3x trilogies) by Sherri S. Tepper has this as its core concept - however the revelation that they landed on a spaceship doesn't come out until the very last book in the set.
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Possibly Saga of Pliocene Exile - Julian May ?
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I'm trying to figure out the title of a series I read when I was younger.As far as I can remember, it started with a spaceship crashing on a planet in book 1.Some plants on that planet had weird effects on the people of the ship, not sure what kind though.  All of the books afterwards are set centuries or even millennia later, about the rebuilt civilization where "magic" or some kind of powers were around.  I'll update if I remember anything more specific.
Looking for name of a book-series - Spaceship crashed, Civilization based on Magic rebuilt
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There are various books that might fit this description. One possibility is the Darkover series by Marion Zimmer Bradley. Other potential answers include the Coldfire Trilogy by C.S. Friedman, the Well World series by Jack Chalker or the True Game series by Sherri S. Tepper. A number of suggestions are made, including the Darkover series, Cycle of Fire, Coldfire, Well World, Saga of Pliocene Exile and True Game.
Perhaps the Darkover series by Marion Zimmer Bradley the Cycle of Fire  books by Janny Wurts which has similar ideas. Perhaps the  Coldfire Trilogy  by C.S. Friedman? It is set on a planet colonized over a thousand years earlier by humans. It could also be the  Well World series  by Jack Chalker, which starts with "Midnight at the Well of Souls". It could be the True Game series by Sherri S. Tepper which has this as its core concept. However the revelation that they landed on a spaceship doesn't come out until the very last book in the set. Possibly Saga of Pliocene Exile by Julian May.