Super roots of Lotus corniculatus are a fast growing legume root culture that allows continuous root cloning, direct somatic embryogenesis and mass regeneration of plants under entirely growth regulator-free culture conditions. These features are unique to root cultures and are now stably expressed since the culture has been isolated almost 5 years ago. Super roots switch from exclusive root proliferation to shoot production upon transfer to light and stationary condition. Lateral root formation continues at a reduced rate while embryos and shoots are forming. When infected with Rhizobium loti, super roots carrying somatic embryos and small shoots, form root nodules. Regenerating super roots provide evidence that root-derived somatic embryos and shoots of L. corniculatus begin to form in a process related to the development of lateral roots or root nodules. When treated with a low concentration of benzylamino purine (BAP) shoots form at an increased rate matching the spacing typical for lateral roots. The super-growing root culture of L. corniculatus regenerates plants that show no morphological differences as compared to wild-type regenerants or seedlings. Roots dissected from plantlets derived from super roots or from super root-derived protoplasts express all super root qualities again when cultured in vitro. Super roots provide a favorable experimental system for developmental studies that are sensitive to exogenous hormones such as lateral root formation or nodulation in vitro.

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The plant body of cereal crops is composed of successive morphological units called phytomers, each of which consists of a stem internode, a leaf, nodal roots and a tiller bud. It has been reported that the number and size of nodal roots should be greatly affected by the number and size of phytomers, respectively. In addition, the bleeding sap rate is often used to evaluate physiological activity of a whole root system without digging up the plants. These two concepts of phytomer formation and bleeding sap rate were used to compare the structure and function of root systems in rice plants (Oryza sativa L.) transplanted at the 2-(“nyubyo”) and 4-leaf stages (“chibyo”) in a farmer's paddy field in the Tochigi Prefecture. Transplanting 2-leaf stage seedlings was recently developed to save the time and labor required with transplanting 4-leaf stage seedlings, which is the conventional practice in Japan. The root system of the nyubyo-transplanted rice had a shallower distribution with slower senescence in physiological activity than that of chibyo-transplanted rice during grain filling. Nyubyo-transplanted rice had a larger number of phytomers (i.e., a larger number of leaves) with smaller size (i.e., a smaller dry weight per phytomer and smaller stem diameter) than chibyo-transplanted rice. These phytomers could form numerous, but somewhat small, nodal roots, which may lead to the shallow distribution of active “superficial roots” in the root system of nyubyo-transplanted rice.

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