Euphorbia sparsiflora is a small subshrub with gray to pale brown bark and ascending, glabrous stems that grow 0.2 to 0.6 meters long and slender flowering branches measuring 1 to 1.5 mm in diameter. The leaves are simple, opposite, and decussate, with blades that are elliptic to obovate or oblanceolate, occasionally spatulate, ranging from 10 to 30 mm in length and 5 to 15 mm in width. Leaf apices are rounded to obtuse, sometimes acute, mucronulate or retuse, and the bases are cuneate and often oblique. The leaf surfaces are glabrous and glaucous, with entire margins. Petioles measure 0.5 to 2.5 mm and are glabrous, while stipules are rounded-triangular, 0.5 to 1 mm long, glabrous, ciliate, erose, and occasionally bifid. The flowers are produced in solitary cyathia in the leaf axils, with glabrous peduncles 1 to 4 mm long. The campanulate involucre measures 1.5 to 2 mm in height and 2 to 3 mm in width, usually glabrous but sometimes sparsely pubescent beneath the glands. Each cyathium has 4 to 5 purple glands, rarely bearing a narrow white appendage. The flowers are unisexual and highly reduced, with a single pistillate flower on a gynophore and staminate flowers arranged in five cymules, each containing one or more flowers. Male flowers are reduced to single stamens, subtended by slender bracteoles, while the ovary is superior with red styles that are shortly bifid to one-fourth their length. The fruit is a glabrous, 3-angled capsule, 2 to 3 mm long, green to red, with recurved gynophores exserted 1.5 to 3 mm from the involucre. The seeds are reddish brown to gray, smooth to faintly rugose, and measure approximately 1.5 mm in length. It is found in bogs between 600-800 meters.