Alphonso is my maternal great, great grandfather. i've lived in Moura for the past 26 years and only realised recently that I have a lot of relatives only a few hours drive away (in Rockhampton).
I don't know if you've been to France yet but De Landelles can literally translate as "From Flanders". Maybe .....? I did 5 yrs of French and find it to be one of the few languages that appeals as it's not harsh or gutteral. But that was a lot of years ago.
There were some early settlers to America called Landa and they were Italian so my friend Jennie tells me.
The Census takers were often semi-literate themselves and the same probably goes for people entering records for embarkation and disembarkation. Also, there may have been some wishful thinking in adding the De to the surname. Trying to go back to better past times perhaps?
If you have any news from over on the Continent, I guess you'll put it up for general viewing. Good luck!
Kind regards, Shielagh West Moura Central Qld Australia