As a child of my mother with relatively early alzheimer's, probably age 65, this has been part of various frights (I've eye frights too). Also, I've got a passel of aunts on my mother's side that were institutionalized in Boston (Metropolitan). I don't know my father's side very well, but his father was a probable scoundrel with issues, also institutionalized. Do you see where this is going? I lost my mother and father in messy horrifying ways in the late sixties and seventies. I don't think about them all the time, all these years later, but I do think and rethink and remember. (I'm 72 now, paying attention) They were both dear, and very different and I sure wish we could talk.
Meantime, after a quite active life, I now have an oddly spare life, re social opportunity in my present home town, not least because of the transportation system I didn't understand is not here.
Since I've been here, now about eight, geez, eight years, I no longer remember all my plant names..
and I knew the latin names of a thousand plants, at the least.
As others have said, I can dig them up. I avoid googleing, right away (how I like to spell that). It is as if I need to get to a more buried layer, and do, in a while. Snap. Of course. There was just that space where I couldn't just say it.
But the new thing now is I'm missing some occasional names of stuff I want to refer to. Gaah. But they too rise up through the morass, so far. A notch down in performance. I've a fairly good english vocabulary but now there are some blotches.
On the other hand - when I first started my landscape architecture classes, I was about to turn forty. Then four years of a lot of stuff. I was pretty good at it, already knew and wasn't afraid of how to draw. Conversant with the teachers, kept doing well, but that was just the start, as site design and grading and urban planning and names of plants and a lot else re the land would come into it.
I remember even then that I simply could not remember the name of a beautiful tree on Motor Avenue.
I did learn plant names to some extent from my seeing then in place, or photos like that.
I do know it now since I've looked it up multiple times over the years, but I had an original memory block. It's Calodendren capense. There, go look.
http://davesgarden.com/guides/pf/showimage/46365/#b