I was noticing that a lot of the current descriptions list a yellow skinned plum but Glen St. Mary listed a red plum in their catalog from 1899. I got a tree from Simpson Nursery and it’s supposed to be the dark red skinned plum described by the original source. Why is there a difference from the original source to all the current yellow skinned descriptions?
This may not answer your question, but the tag on the plum in your hand looks to be ‘Excelsor’ not ‘Excelsior’ (with an “i”). Lowes apparently sells a variety it calls ‘Excelsor’ which it identifies as Prunus salilcina, a straight Japanese plum, not the supposed Goose plum cross from the nursery catalog.
I mean, calling it salicina could be just as accurate as calling it a munsonia. It is a seedling of Kelsey after all. But regardless of the spelling or what I have, the original source lists a red plum but all/most current sources describe a yellow Plum that sound more like Byrongold, 2" yellow Plum.