The bottom design is known as spurless, but I am not sure those parts are universally understood as a spur. Foot might work.
Yes, spur is the term.
They don’t have a separate name. They are just the bottom of the stem.
A ‘spur’ is usually the bit on the bottom right of the cap G that points down – and does imply pointiness. ‘Foot’ only works if they’re at the bottom – they appear on the top on a p or q.
How about ‘Prong’?
Flange
Protuberance
Knob
Appendage
Nodule
Offshoot
Excresence
Apophysis
Barb
Nubbin
Limb
Extender
Thingy
I don’t think there is an official term but I like nubbin. I would be tempted to call them “the nubbin at the bottom of the stem,” if I was trying to describe them to someone 
Prong is nice too.
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Prong is my frontrunner
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