As far as my experience as an herbalist goes, German and Roman Chamomile are often used interchangeably. They do however contain different volatile oils/constituents and I have read that Roman Chamomile may be more antioxidant than German chamomile. They smell slightly different from one another and German chamomile contains azulene, which gives the essential oil its blue color (making it more anti-inflammatory and great for topical skin use). German chamomile might also be slightly less allergenic than Roman chamomile and have more anti-bacterial properties. Roman chamomile contains a high percentage of esters, which are helpful as an anti-spasmodic.
Pineappleweed is used similarly to German chamomile I believe!