Across:
   1. see 23 down
   4. In unusual woods, hunt with the penguins perhaps? (4 5)
   9. Sadly cuts clue about new form of plant (9)
  10. You might wear it during flan or pancake flipping (5)
  11. Hypothetical places to go from and to, and what facilitates it at large? (6)
  12. Cannonball perhaps strangely deadly, filled with germ inside (8)
  14. Old oil chart is inaccurate (10)
  15. Do opposite of 18: allow coke regularly (4)
  18. Do opposite of 15, now peeing regularly (4)
  20. In spouse, I get art slowly turning cunning (10)
  23. To do with having issues in shop (a rent altercation) (8)
  24. Quiet graduate, one in big city (6)
  26. Hacked trees can be put back? (5)
  27. Grappling with others having fish (9)
  28. Talked down country in south east (communist) (9)
  29. Animal's work at wheel thrown when edges lost (5)
Down:
   1. CIA to ship "mixed nuts" obtained from this plant (9)
   2. see 23 down
   3. Might she teach him a lesson, and miraculously cure toad? (8)
   4. Perhaps one of two does opposite of 25? (4)
   5. It's not as safe as abstinence ... nonetheless, having child rejected (10)
   6. Test as liquid plasma and gas perhaps (6)
   7. Maurice, painter and hunter, kills lion regularly (7)
   8,16. Departed queen getting affection from departing grandson and 23 1 2 negotiator? (5 9)
  13. Conflict with a new aim: TV to be managed right (7 3)
  16. see 8
  17. 23 1 2 negotiator headed 22 court with revolutionary leader (2 3 3)
  19. Massive land area is about to get 22? (7)
  21. Integral of root of negative unity nil but changing (7)
  22. Tune I'd played in combo (6)
  23,1ac,2. Deal outlining 22 6 5 from 13... a sad caprice, corpse-scattered (5 5 7)
  25. Perhaps one out of two playing bassoon, opposite of 4? (4)