We have the same plant on our property. Zone 9b. Central Florida. This is a wild blackberry. We have found several of these with small berries on them. Noticed the berries in June. plants are maybe a foot tall. 3 Leaflets one stalk. All the plants we have look new. We cleared some land and this year they appeared. Deer probably seeded the area.
Hope this info helps.

So, were you able to get the answer? Same thing to me. Google says it could be blackberry, but nothing about horrible rash.

Interesting. The Wikipedia article does state that the second year cane produces 3 – 5 leaflets. http://en.wikipedia.org/wiki/Blackberry It also says that the second year canes would produce blooms and fruit. Hmmm? The mystery deepens with this recent post to the Gardening Guru of the World! http://www.walterreeves.com/name-that-plant/thorny-invasive-weed/ Yours look a little different to me. What do you think? And finally, from the good folks at NC State we have this link http://www.turffiles.ncsu.edu/weeds/Blackberry.aspx. On yours I’ll stick with the common blackberry. With weed ID i’ve acquired a taste for crow!

Wikipedia research indicates that this is not a blackberry plant. Blackberry plants have leaf groups of 5 -7 per stem. This plant has only 3 leaves per stem and no evidence of berries. Anyone else have some ideas?

Blackberries make good jams, jellies and, I understand, pretty good communication devices. I am unsure about that last one cause I’ve never cooked ’em that long. It does seen that the briars would be a little rough on the ears. You can use Roundup to get rid of them or a good pair of heavy gloves to just pull them up. Avoid the briars cause they can be really tough on the hide but I’ve never had a rash from them. Now chiggers from ’em is a whole ‘nuther story.