Herb
The pot marigold, opening with the sun and closing before rain, more or less.
These are associations the community holds, not settled fact — the more a reading is shared, the bolder it sits.
The pot marigold is not the African or French marigold of bedding schemes; it is a different genus entirely, and the confusion in shops is unhelpful. Calendula is the old kitchen and physic-garden plant, orange or yellow, flowering from spring until a hard frost and self-seeding forever after.
Its name comes from the calends, the first day of the Roman month, on the reasonable grounds that it seems to flower in all of them. The flowers open and close with the light, which gave rise to a widespread piece of weather-lore — marigolds closed in the morning mean rain — and to a solar correspondence that is about as intuitive as these things get. Petals coloured butter and cheese and stretched saffron for people who could not afford saffron.
Practice uses calendula for the sun, for warmth, for legal matters and for seeing truly, the last from an old English recipe for a salve that was supposed to let you see the fair folk. Its long external use on skin is genuine and continuing, which does not make it a medicine.
Readings practitioners have offered, ordered by how many recognise them. Take what serves, leave the rest.
Carried forward
Nicholas Culpeper, The Complete Herbal (1653)
Culpeper is unambiguous: it is an herb of the Sun, and under Leo. He also passes on the belief that merely looking at marigolds strengthens the sight, which is a nice illustration of how a colour becomes a claim.
Carried forward
English recipe books, sixteenth and seventeenth century
A salve of marigold flowers gathered at a particular time appears in more than one manuscript as a means of seeing the fair folk. The recipes are elaborate, mutually contradictory, and were plainly copied from one another rather than tested.
Credit what you carry. Much of this comes from living traditions, and some of it from traditions that are closed — held by particular peoples and not offered for general use. Where you know whose practice a reading came from, name them; where you don't, say that too.