A fungus. In Asia it is Sporothrix globosa.
Found in rotting organic material, it is most often due to percutaneous injury.
Ascending nodular lymphangitis (it forms bumps in the lymphatics where the nodes are not), occasionally infected joints and pneumonia (primarily in poor hosts); AIDS patients can get a disseminated disease (PubMed).
Sporothrix globosa causes sapronose: " human diseases transmissible from abiotic environment (soil, water, decaying plants, or animal corpses, excreta, and other substrata)(PubMed)."
A saturated solution of potassium iodide (SSKI) begin with 5 to 10 drops po tid and increase to 40 to 50 drops tid is the traditional treatment. Cutaneous disease can be treated with itraconazole at 100 mg/d (duration is until all gone) (PubMed) and widespread us usually treated with amphotericin B.
Forget about the rose thorn, it is a nice source of a puncture wound, but any puncture covered with organic material can cause disease.