A term used historically in the American West, "rustler" was usually coupled with cattle. If one stole cattle one was a cattle rustler. Now, if one stole horses, the term applied was horse thief. Horse rustlers just didn't exist.
Cattle rustlers were at times reviled, arrested, and/or put to death by vigilantes or the legal system and at other times ignored, released without prosecution, or found innocent despite obvious guilt if brought to trial. They were commonly seen as heroes of legends, books and movies. Prosecution began in earnest after large land barons found rustling affecting their "bottom line".
Cattle rustling was a profession and a "legitimate" opening to cattle ranching for some. A cattle rustler stole branded cattle (unbranded cattle were not felt to belong to anyone) and altered the brands. In the early American West, cattle roamed the land freely and ownership was determined by brand more than location. Calves not yet branded but still following their mother were considered property of the mother's owner. Calves not branded and not following their mother were up for grabs; consequently calves were branded while still quite young during annual "round-ups" (they were also easier for the cowboys to handle while young). "There were two types of branding iron, the stamp iron which included the full brand and the running iron which had a hooked tip that could be used to change or make any brand."
Much of the information in the paragraph and quote above came from this website
http:/www.linecamp.commuseumsamericanwestdefinethewestcattlerustler/cattlerustler.html
The term rustler has more recently been applied to the practice of propagating old varieties of roses found in cemeteries and old home sites. After the advent of modern hybrids "old roses" were seen less and less in commerce and many were or may be in the process of becoming extinct. The fact that they are long lived plants require little in the way of human attention yet are easy to propagate from cuttings plus the rising popularity of "antique roses" in the last 20/30 years has led to the practice of "Rose Rustling". This practice involves taking cuttings from a plant, rooting them and growing clones of the original plant. Advocates have rules of etiquette and strive to not alienate landowners. Rose rustling is in fact the acknowledged source of many "old roses" now back in rose catalogs.
The term rustle has also been applied to the large-scale harvest and theft of commercial Christmas trees. My mom used to have a Christmas tree farm and this was a major problem.
I have also seen the term used once to describe the practice of uprooting and stealing recently installed landscaping plants in the Washington Post.
I myself am a leaf and grass clippings rustler. I make my midnight rounds of the neighborhood on the night before the recycling truck comes to do curb side pick up of yard wastes. Our county composts this material instead of putting it in the landfills but I like to make my own. I use the materials to make huge compost piles. I do it at midnight, not because I believe it to be stealing but....it is considered a little "weird" by many.
I also plan to rustle some native plants in the way of a major highway construction project. Left alone they will simply be plowed under. Under other circumstances I would not dig wild plants but I will now look hard for any rarities I can "rescue" by rustling. | 
