Green’s Dictionary of Slang

plain-Jane-and-no-nonsense n.

also straight-Jane-and-no-nonsense

(Aus.) without unnecessary adornment, ‘no frills’.

[Aus]Bendigo Indep. (Vic.) 1 May. 6/2: ‘Well, take him to the kitchen and plant him on the rug in a plain-Jane-and-no-nonsense manner, and Elspeth’ll swallow him, I bet’.
Land (Sydney) 7 Mar. 13/1: Not a bit o’ trimming, not a frill or a fancy, can I indulge in just ‘plain Jane, no nonsense’ from start to finish - and I do so love a bit of foolishness, too!
[Aus]Sydney Morn. Herald 16 Jan. 3: [advert] Gone are the days when handbags were ‘Plain Jane and no nonsense’ affairs, designed expressly for business and not for pleasure of the user or beholder.
Goulburn Eve. Post (NSW) 1 Oct. 4/2: [advert] In Grandma’s day Aprons were Aprons. They were ‘plain Jane and no nonsense’.
[Aus]Mercury (Hobart) 18 Sept. 20/5: The old days when there was nothing between the ‘Plain Jane-No-Nonsense’ type of shoe for the growing girl, and the sophisticated styles of the adult have gone forever.
[Aus]Canberra Times (ACT) 8 May 4/2: ‘My part in “Fair Go” is very much a straight-Jane, no-nonsense one. There is some very funny comedy in the show,’ she said.