Prize-winning crossword

When all the answers are in place, the letters in the even-numbered squares in the grid will spell out the surnames of three people who have had plants named after them. ACROSS 1 Compliance with a request or order (9) 6 Prefix meaning relating to rotation (4) 10 and 11 Organisation that cares for gardens at Sheffield Park and Stowe, for example… (8,5) 12 …and this building at Quarry Bank (4) 13 1969 film starring Peter Fonda and Dennis Hopper (4,5) 18 Plant also known as love-in-a-mist (7) 20 Citrus fruits (7) 24 Name of Cambodia before 1989 (9) 27 Beware the ___ of March (4) 28 Wall-painting (5) 30 1980 hit for OMD (5,3) 31 Churchyard trees, perhaps (4) 32 Lavender genus (9) DOWN 2 South American country, and a type of nut (6) 3 Sows seed in a small, machinemade furrow (6) 4 Late comedian Mr Wise, perhaps (5) 5 Smallest structural units of a plant (5) 7 Not me! (3) 8 Semi-aquatic animals of the weasel family (6) 9 Began (7) 14 Queen of England, 1702-14 (4) 15 Aromatic herb of the parsley family (4) 16 Very serious, forbidding (4) 17 Plants that live for only a year (7) 19 Man or Wight, perhaps (4) 21 Meagre, providing less than is required (6) 22 Promontory that is the southernmost point of Britain (6) 23 Remember, bring to mind (5) 25 Dog-like African animal (5) 26 Pleasant smell (5) 29 Number of things in a line (3)