It would be helpful if you told us what plant species the compounds came from.

You could try looking them up in CHEBI (http://www.ebi.ac.uk/chebi/ ) (free resource)

Also, look up the plant genus and species in the following resources:

Journal of Natural Products/ ACS (American Chemical Society) Journal search

Science Direct

PubChem (http://pubchem.ncbi.nlm.nih.gov/ ) (Free resource)

These are all on-line and your university may already have subscriptions to the ACS and Science Direct libraries- these charge a fee for downloading if you don't have a subscription.

Without more data like a full fragmentation pattern, or NMR, it is impossible to sort out which of the multitude of structural possibilities these molecular formulas represent. A quick Chemexper search (see link) of these molecular formulas gives ammonium palmitate as the only available compound for C16H35NO2. So my guess is palmitic acid ammonia adduct [M+NH3]+. A similar search for C18H39NO3 gives 17 possibilities, one of them being palmitic acid ethanolamine salt [M+C2H7NO]+. A search on C17H37N3 gives 51 possibilities, one these being 2-hexadecylguanidine.  I based the last 2 guesses on these compounds being similar to the first compound since they all probably would partition in the extract the same way.

https://www.chemexper.com/