Theme: Tree - Last word is parts of a tree.
18A. Thin, decorative metal : SILVER LEAF
23A. Gets married : TIES THE KNOT
37A. Dangerous things to risk : LIFE AND LIMB
48A. Equestrian's supply box : SADDLE TRUNK
56A. One, to one, e.g. : SQUARE ROOT
Argyle here. No unifier but you shouldn't have needed it. The entries run top to bottom of a tree, more or less. A few extra black squares gives a unique look to the grid but nothing special that I can see. Cruciverb is back up(I hope) but everything Google is messed up.
1. Cathedral area : APSE
5. Tons : SCADS
10. Reps: Abbr. : AGTs
14. Garden center supply : SEED
15. Dot in the ocean : ISLET. Did you know ait or eyot is an islet, esp in a river . (British dialect)
16. Circus performer? : FLEA
17. Tune : SONG
20. What a 63-Across may speak : ERSE. 63A. Hebrides native : GAEL. Off the west coast of Scotland.
21. The last Mrs. Chaplin : OONA. Daughter of Eugene O'Neill.
22. Grand Rapids-to-Detroit dir. : ESE
27. This, to Michelle : CET. For a masculine word beginning with a vowel, right?
28. Morose : SAD
29. Geometric suffix : GON
30. Like potato chips : SALTY
32. Lulus : DILLIES
36. Mass transit carrier : BUS
39. Retirement destination? : BED
40. Wimps : SISSIES
41. Underworld group : MAFIA
43. Printer's widths : EMs. The "em" value is based on the width of the uppercase M. We've had a better explanation before but the blog search is on the fritz.
44. Cookie container : JAR
47. Renoir output : ART
53. Spoil : ROT
55. "Picnic" playwright : INGE. Labor Day picnic in Kansas, 1953.
60. "Ain't Misbehavin'" Tony winner Carter : NELL. Clip from the musical. (Catch a small shout out to Erie, PA)
61. Throw hard : HURL
62. Hero's quality : NERVE
64. Desires : YENS
65. Burning desire? : ARSON. Mini-clecho.
66. Chop __: Chinese American dish : SUEY
1. Valuables : ASSETS
2. Illinois city that symbolizes Middle America : PEORIA
3. Had a hunch : SENSED
4. Barely beats : EDGES
5. Member of the fam : SIS
6. CBS drama with two spin-offs : CSI. (Crime Scene Investigation)
7. "Everything's fine" : "ALL OK"
8. Exeter's county : DEVON
9. Dictation whiz : STENO
10. The K.C. Chiefs represented it in Super Bowl I : AFL. American Football League, operated from 1960 until 1969.
11. High school choral group : GLEE CLUB
12. Dollhouse cups, saucers, etc. : TEA SETS
13. Protected condition : SAFETY. Clue seemed awkward to me but valid.
19. Pied Piper followers : RATS
24. End-of-the-workweek cry : TGIF
25. Pebble Beach's 18 : HOLEs. Par 72 (blue tees)
26. China's Zhou __ : ENLAI
31. SALT concerns : ABMs. (Anti-ballistic missile)(Strategic Arms Limitation Talks)
32. "__ say something wrong?" : DID I
33. Elected ones : INs
34. '50s automotive failure : EDSEL
35. Goo : SLIME
37. There's a lane for one at many intersections : LEFT TURN
38. Superlative suffix : IEST
39. Like Bach's music : BAROQUE. Bach
41. Boggy : MARSHY
42. Solar system sci. : ASTRonomy
44. Alaskan capital : JUNEAU
45. "Crouching Tiger, Hidden Dragon" director : ANG LEE
46. "I Believe I Can Fly" singer : R. KELLY. Video It starts out so lovely then the boom box comes in...ugh!
49. Stadium : ARENA
50. More desperate, as circumstances : DIRER
51. Some portals : DOORS. And a trio.
52. Adornments for noses and toes : RINGS
57. Gore and Green : ALs
58. Lacto-__ vegetarian : OVO. They do eat eggs and dairy products.
59. Years in a decade : TEN