Welcome aboard, Coub
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You'll find this a very friendly & helpful site, loaded with info.
The only ornamentals I'm growing are Basjoo & Zebrina so I can only guess at the Maurelii. Two possibilities exist that I'm aware of. My Basjoo is showing identical symptoms. I suspect either nematodes (can be common in overly rich soils) or too much sunlight. Are you growing it indoors or out?
BTW, it will help us, to help you more, if we know more about your growing zone & weather
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