Get Outdoors - DayHike: Leave What You Find

Allow others a sense of discovery by leaving rocks, plants, archaeology artifacts and other objects of interest as you find them.Leave areas as you find them. Good campsites are found and not made.

Do not dig trenches for tents or construct lean-tos, tables, chairs, or other rudimentary improvements.
If you clear an area of surface rocks, twigs or pine cones, replace these items before leaving.
On high impact sites, it is appropriate to clean up the site and dismantle inappropriate user-built facilities, such as multiple fire rings and constructed seats or tables.

Avoid damaging live trees and plants.

Picking a few flowers does not seem like it would have any great impact and, if only a few flowers were picked, it wouldn't. But, if every visitor thought I'll just take a few, a much more significant impact might result.
Take a picture or sketch the flower instead of picking it.
Experienced campers may enjoy an occasional edible plant, but they are careful not to deplete the surviving vegetation or disturb plants that are rare or are slow to reproduce.

Leave natural objects...

Natural objects of beauty or interest such as antlers, petrified wood, or colored rocks add to the mood of the backcountry and should be left so others can experience a sense of discovery. In National Parks and some other areas it is illegal to remove natural objects.

...and cultural artifacts.

The same ethic is applicable to cultural artifacts found on public land. Cultural artifacts are protected by the Archaeological Resources Protection Act. It is illegal to remove or disturb archeological sites, historic sites, or artifacts such as pot sherds, arrowheads, structures, and even antique bottles found on public lands.