The status of a younger branch of a family:the arms of younger sons are differenced by marks of cadency...
The rose is the emblem of England and in heraldry is used as the mark of cadency for a seventh son.
The trine aspect to the ascendant and association with the Sun helps to alleviate the more negative associations of cadency.
Marks of cadency are determined and granted for life to the individual by Royal Warrant (from the 19th century, members of the Royal family do not have arms until assigned to them, and these arms are not necessarily inheritable).
Origin
Early 17th century (in the sense 'rhythm or metrical beat'): based on Latin cadent- 'falling', from the verb cadere. The current sense is apparently by association with cadet.