Sorghum vulgare var. technicum is commonly called broomcorn. An annual grass like other Sorghums, it grows 6 to 15 feet tall, although dwarf varieties are only 3 to 7 feet in height. The upper peduncle is normally 8 to 18 in long, topped by a branched inflorescence or panicle which originate the seed-bearing fibers. The fibers are usually 12 to 24 inches long but can be up to 36 inches long; they are branched toward the tip where the flowers and seed grow. The seeds weigh about 30,000/pound, with feed value similar to oats. A ton of the fibrous panicle makes 900 to 1200 brooms.[7]

Plants selected for long panicle branches probably originated in central Africa, but the variety was known to be used for broom-making in the Mediterranean in the Dark Ages. It was first described in Italy in the late 1500s.
[Note: this pre-1923 publication has been converted from its original form for the Kindle and may contain an occasional defect from the conversion or from the original publication.]