This mutant arose in MacArthur's X-rayed stock and is characterized by extreme reduction of the internodes so that all the leaves emerge from the region just above the cotyledons. The mutant never flowers, but one or two year old plants do occasionally produce vestigial flower buds. Old plants with 50 - 100 nodes rarely reach a height of six inches as opposed to 10 - 15 feet in normal ones of similar age. Cotyledons are persistent for a long period but never become enlarged, and the hypocotyl is shortened. Axillary branching is also supressed; the few side shoots of this mutant present an extreme contrast with the mutant bushy (bu) that arose in the same X-rayed stock. A pleiotropic effect of the ro gene is the reduced branching of the roots. Usually this mutant produces a single tap root which contrasts greatly with the mass of rootlets in normal plants of the same age. The leaflets in this mutant are narrower than in normal plants.
The mono-hybrid ratios show a deficiency of mutant types, a typical ratio being 462:105 with a chi square of 12.7. Rosette is in linkage group I being linked with dwarf with a cross-over value of 20.9% as shown by the dihybrid ratio ++ 782: +d 342: ro + 235: d ro 11.