1NOT KNOWsomeone who is not trained in a particular subject or type of work, especially when they are being compared with someone who is 门外汉,外行人 → laywomanOPP expert
To the layman (=laymen in general) all these plants look pretty similar.
对外行的人来说,这些植物看起来都很相似。
If you don’t understand what the doctor says, ask to have it explained in layman’s terms (=in simple language).