That took me a little by surprise as I realised I was ignorant of how the opposition process worked in Holyrood as opposed to that of Westminster. Taking the source below as reference rather than authoritative, this is what Wiki has to say about it:
en.wikipedia.org
It seems there is no recognised official opposition as such, unlike the national Parliament, so each non-government party is free to set up it's own shadow as much as it wants (or can). Checking this against the official source (
Party Leaders and Spokespersons - Parliamentary Business : Scottish Parliament) this appears to be correct.
It is intriguing that the SC&U has deliberately separated the Party leader from that of the the Leader of the Party MSPs. I wonder if that will continue after wee Ruthie leaves?