I thought I had this all but complete (except 17Dn), until l read the comments above.
For 17 (Ladies' hat-maker cut amount of advertising space available (7) I have N?L?INE, with my 16Ac being ALNUS. I'd appreciate some help with this one.
My arboreal meanderings appear to differ somewhat from thoseof other solvers. My current 2nd letter for 36Dn is a U, as I thought TULIP might fit the bill. I'm now thinking the category must be limited to LATIN taxonomy, making 40 a slightly amusing homophone. This still wouldn't solve the dilemma at 2Dn, which I share with some other dissatisfied customers. Glad to see my favourite setter given a name-check.