Preheat oven to 350°F (175°C).

Butter and flour two jelly roll pans (10- by 15-in.).

Beat egg whites until soft peaks form. Set aside.

In a separate bowl, beat egg yolks with granulated sugar until thickened.

Beat in vanilla, then add flour and blend.

Fold in egg whites gently.

Divide batter between prepared pans and spread evenly.

Bake for 15-17 minutes, until golden brown and springy.

Cool cakes for 3-4 minutes.

Loosen cakes from pans and invert onto powdered sugar-dusted towels.

Peel off parchment paper and cool completely.

Make filling: Beat heavy cream, vanilla, and powdered sugar until thick.

Fold in chopped almonds.

Soften prickly pear jelly and spread on each cake, leaving a 1-in. border.

Drop whipped cream over jelly and spread evenly.

Roll each cake into a log.

Cut parchment strips for serving board protection.

Set one cake log seam side down on parchment.

Cut parchment strips for arm supports.

Slice remaining cake in half crosswise.

Cut one smaller roll lengthwise diagonally to create two triangles.

Place triangles on parchment strips, one seam side up and one seam side down.

Cut the remaining smaller roll crosswise into two round slices.

Place round rolls on parchment strips, seam side down.

Make frosting: Beat cream cheese and butter until blended.

Mix in lemon juice, lemon zest, and powdered sugar until smooth.

Add leaf-green food coloring, then black and golden yellow for a sage-green color.

Press top end of saguaro stem into a rounded shape.

Frost the saguaro stem, leaving the bottom end unfrosted.

Generously frost the triangle and round pieces for the arms.

Use a fork to create vertical stripes on the saguaro stem.

Remove parchment from under the cakes.

Carefully lift and attach triangle arms to the stem.

Set round cake rolls on top of cake triangles.

Use reserved frosting to fill gaps between triangles and rounds.

Create stripes on each arm.

Dust cake with gold pearl dust.

Place Meringue Saguaro Flowers on each arm.