Elite cannabis genetics aren't shared with just anyone who asks for them. Growers pride themselves on holding certain rare strains close -- and dispensaries have been known to hoard them. For these reasons, you don't often see anyone freely distributing clones of hard-to-find strains. So it's surprising (and refreshing) to see a dispensary not only making a rare, medically beneficial strain available to the community, but to do so without charge.

Denver-based Greenwerkz medical marijuana dispensary has been touting R4, its CBD-rich strain, for years now, and with good reason. Unlike its cannabinoid counterpart THC, which is known for the "high" associated with marijuana, CBD has been found to alleviate pain with few to no mind-altering effects. While a high CBD amount for a normal strain would be up to 3 percent by weight, R4 has consistently clocked in at between 14 and 20 percent CBD. Not only that, but it also has ultra-low THC -- at times lower than 1 percent.

But getting the strain -- both in clone and seed form -- comes with stipulations: The genetics can't be resold (only gifted); any strains created using R4 have to be available to Greenwerkz; and, most notably, the finished buds can't be sold for more than $15 an eighth.

"We believe that this strain provides wonderful attributes to both patients and growers," says Kelly Roller, Greenwerkz vice president of cultivation. "We have had many patients who come in just for the R4. It really does provide a lot of patients pain relief without the cerebral/psychoactive 'high' typically associated with cannabis, and we wanted to share that with the community."

I checked out Greenwerkz back in July 2011 specifically to see how the already well-known R4 would ease chronic back pain I was experiencing at the time. My take? While the strain isn't the most beautiful belle at the ball, she sure knows how to dance.

"The report from Full Spectrum Labs showed that it was 14.55 percent CBD and less than 1 percent THC, just a hair over what can be found in industrial hemp plants," I wrote. "For all I know, this could be from an industrial hemp plant, as Carstens didn't give any hints to its lineage. It had leafy, underdeveloped-looking buds -- though I've never seen this cut or anything related to it with which I can compare it, so maybe that's just how it grows. Very waxy-feeling, and under the scope you can see globs of plant resin on the teeny, tiny dark-green sugar leaves. It smelled like a hemp shirt when broken up, and the taste wasn't much better. But taste aside, the CBD content is noticeable within five minutes of smoking a hefty bowl. Without a doubt, it helped ease my back pains, especially at night, when lately I've been jolted out of sleep by searing nerve pinches."

Greenwerkz folks ask anyone interested in the strain to contact them at info@greenwerkz.com or stop by their booth at the em>High Times Cannabis Cup over the 4/20 weekend. They say the strain should be ready to roll out by April.

More from our Marijuana archive: "Marijuana: A64 task force member says buying limits about diversion, not jacking up prices" and "Marijuana-friendly coffee shop sues Lafayette to fight city's pot-business ban."