Solution to Seasons Greetings XV by Eclogue.

 Seasons Greetings  XV by Eclogue SOLUTION

I SAW THREE SHIPS sounded like EYESORE (BLOT, STYE) TREE (GEAN, NEEM) SHAPES (SQUARE, TRIANGLE).  Three triangles are to be drawn through ARGO, MARY ROSE and THE MAYFLOWER to produce the Christmas tree image.

Across

1 VARIATION C1 = square; 

5 THEMEWORD A = eyesore; 

O 11 tunnel; TUN + N[O]EL<

13 Anglos; hidden; americAN GLOSsary

N 14 yelt; [N]YE + LT

C 15 airn; [C]AIRN

16 VARIATION A1 = blot; 

17 Eloisa; EL + O + ISA; REF. Louis A.

H 19 ogee; GO< + [H]EE(l)

R 20 kegs; initials; K E [R] G S

21 rest; two meanings

23 uric; initials; U R I C

I 26 Kyra; hidden; quirKY R[I]Ant

S 27 meseta; (MET SEA[S])*

T 29 Ramism; [T]RAM + ISM

M 31 yerded; (DRY + DE[M]E)*

32 imides; (SE + DIM + I)<

34 lo-fi; foil*

A 37 arch; initials; A R [A] C  H

S 38 trew; [S]TREW

D 41 loci; COL[D]< + I

A 43 stot; STO[A]T

45 Agatha; GAT in AHA; Ref. A Christie

47 VARIATION B1 = gean; 

Y 48 orra; OR + RA[Y]

49 VARIATION B2 = neem; 

50 lawmen; ME in LAWN

51 Eskimo; ESK + I + MO

I 52 endorse; ROSE* after EN[I]D

53 THEMEWORD C = shapes; 

Down

1 VARIATION A2 = stye; 

2 quelea; QU + E + LEA

N 3 antiskid; STAIN* + KI[N]D

T 4 reasty; (AR[T]Y SET)*

5 euro; ROUE*

6 yangs; NG in SAY<

H 7 entêtée; [H]EN+TET+E(y)E

E 8 olla; L[E]O< + LA(p)

M 9 roopit; ROO[M] + PIT

O 10 estacade; EAST* + C[O]DE around A

12 liar; RAIL<

R 18 ogamic; [O + G[R]IMAC(e)]*

N 22 eagle; EA + GLE[N]

24 red-hot; (HORDE)* + T

25 VARIATION C2 = triangle; 

28 Sri Lanka; RIS(HI)  SRI + LANK + A

30 settler; (L + STREET)*

I 33 Mr Bean; (A[I]M BREN)*

N 35 fogash; FO + G[N]ASH

36 scheme;  CH in EMES<

G 39 roons; R + [G]OONS

40 ware; RAW< + E

42 bawd; W in BAD

44 THEMEWORD B = tree; 

46 Amos; hidden; medinA MOSque