What I have found is that -
Dendrobium aphyllum is syn. to Dendrobium pierardii = to your photo #1
and ...
Dendrobium cucullatum is syn. to Dendrobium pierardii var. cucullatum = photo #3
but then I have also found this -
"Dendrobium pierardii Roxburgh -- as D. aphyllum (Roxburgh) C. Fischer
Dendrobium pierardii var. cucullatum (R. Brown) Hooker f. -- as D. aphyllum (Roxburgh) C. Fischer"
(as per
Sheet List- Dendrobium )
so it's a big roundy round loop ..
siting 2 different looking species as one
I'm just as confused